Definition of the word ecology

Ecology

Ecology addresses the full scale of life, from tiny bacteria to processes that span the entire planet. Ecologists study many diverse and complex relations among species, such as predation and pollination. The diversity of life is organized into different habitats, from terrestrial to aquatic ecosystems.

Ecology (from Ancient Greek οἶκος (oîkos) ‘house’, and -λογία (-logía) ‘study of’)^[A] is the study of the relationships among living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps with the closely related sciences of biogeography, evolutionary biology, genetics, ethology, and natural history. Ecology is a branch of biology, and it is not synonymous with environmentalism.

Among other things, ecology is the study of:

• The abundance, biomass, and distribution of organisms in the context of the environment
• Life processes, interactions, and adaptations
• The movement of materials and energy through living communities
• The successional development of ecosystems
• Cooperation, competition, and predation within and between species
• Patterns of biodiversity and its effect on ecosystem processes

Ecology has practical applications in conservation biology, wetland management, natural resource management (agroecology, agriculture, forestry, agroforestry, fisheries, mining, tourism), urban planning (urban ecology), community health, economics, basic and applied science, and human social interaction (human ecology).

The word ecology (German: Ökologie) was coined in 1866 by the German scientist Ernst Haeckel. The science of ecology as we know it today began with a group of American botanists in the 1890s.^[1] Evolutionary concepts relating to adaptation and natural selection are cornerstones of modern ecological theory.

Ecosystems are dynamically interacting systems of organisms, the communities they make up, and the non-living (abiotic) components of their environment. Ecosystem processes, such as primary production, nutrient cycling, and niche construction, regulate the flux of energy and matter through an environment. Ecosystems have biophysical feedback mechanisms that moderate processes acting on living (biotic) and abiotic components of the planet. Ecosystems sustain life-supporting functions and provide ecosystem services like biomass production (food, fuel, fiber, and medicine), the regulation of climate, global biogeochemical cycles, water filtration, soil formation, erosion control, flood protection, and many other natural features of scientific, historical, economic, or intrinsic value.

Levels, scope, and scale of organization[edit]

The scope of ecology contains a wide array of interacting levels of organization spanning micro-level (e.g., cells) to a planetary scale (e.g., biosphere) phenomena. Ecosystems, for example, contain abiotic resources and interacting life forms (i.e., individual organisms that aggregate into populations which aggregate into distinct ecological communities). Ecosystems are dynamic, they do not always follow a linear successional path, but they are always changing, sometimes rapidly and sometimes so slowly that it can take thousands of years for ecological processes to bring about certain successional stages of a forest. An ecosystem’s area can vary greatly, from tiny to vast. A single tree is of little consequence to the classification of a forest ecosystem, but is critically relevant to organisms living in and on it.^[2] Several generations of an aphid population can exist over the lifespan of a single leaf. Each of those aphids, in turn, supports diverse bacterial communities.^[3] The nature of connections in ecological communities cannot be explained by knowing the details of each species in isolation, because the emergent pattern is neither revealed nor predicted until the ecosystem is studied as an integrated whole.^[4] Some ecological principles, however, do exhibit collective properties where the sum of the components explain the properties of the whole, such as birth rates of a population being equal to the sum of individual births over a designated time frame.^[5]

The main subdisciplines of ecology, population (or community) ecology and ecosystem ecology, exhibit a difference not only in scale but also in two contrasting paradigms in the field. The former focuses on organisms’ distribution and abundance, while the latter focuses on materials and energy fluxes.^[6]

Hierarchy[edit]

The scale of ecological dynamics can operate like a closed system, such as aphids migrating on a single tree, while at the same time remaining open with regard to broader scale influences, such as atmosphere or climate. Hence, ecologists classify ecosystems hierarchically by analyzing data collected from finer scale units, such as vegetation associations, climate, and soil types, and integrate this information to identify emergent patterns of uniform organization and processes that operate on local to regional, landscape, and chronological scales.

To structure the study of ecology into a conceptually manageable framework, the biological world is organized into a nested hierarchy, ranging in scale from genes, to cells, to tissues, to organs, to organisms, to species, to populations, to communities, to ecosystems, to biomes, and up to the level of the biosphere.^[8] This framework forms a panarchy^[9] and exhibits non-linear behaviors; this means that «effect and cause are disproportionate, so that small changes to critical variables, such as the number of nitrogen fixers, can lead to disproportionate, perhaps irreversible, changes in the system properties.»^[10]: 14

Biodiversity[edit]

Biodiversity (an abbreviation of «biological diversity») describes the diversity of life from genes to ecosystems and spans every level of biological organization. The term has several interpretations, and there are many ways to index, measure, characterize, and represent its complex organization.^[12][13][14] Biodiversity includes species diversity, ecosystem diversity, and genetic diversity and scientists are interested in the way that this diversity affects the complex ecological processes operating at and among these respective levels.^[13][15][16] Biodiversity plays an important role in ecosystem services which by definition maintain and improve human quality of life.^[14][17][18] Conservation priorities and management techniques require different approaches and considerations to address the full ecological scope of biodiversity. Natural capital that supports populations is critical for maintaining ecosystem services^[19][20] and species migration (e.g., riverine fish runs and avian insect control) has been implicated as one mechanism by which those service losses are experienced.^[21] An understanding of biodiversity has practical applications for species and ecosystem-level conservation planners as they make management recommendations to consulting firms, governments, and industry.^[22]

Habitat[edit]

The habitat of a species describes the environment over which a species is known to occur and the type of community that is formed as a result.^[24] More specifically, «habitats can be defined as regions in environmental space that are composed of multiple dimensions, each representing a biotic or abiotic environmental variable; that is, any component or characteristic of the environment related directly (e.g. forage biomass and quality) or indirectly (e.g. elevation) to the use of a location by the animal.»^[25]: 745 For example, a habitat might be an aquatic or terrestrial environment that can be further categorized as a montane or alpine ecosystem. Habitat shifts provide important evidence of competition in nature where one population changes relative to the habitats that most other individuals of the species occupy. For example, one population of a species of tropical lizard (Tropidurus hispidus) has a flattened body relative to the main populations that live in open savanna. The population that lives in an isolated rock outcrop hides in crevasses where its flattened body offers a selective advantage. Habitat shifts also occur in the developmental life history of amphibians, and in insects that transition from aquatic to terrestrial habitats. Biotope and habitat are sometimes used interchangeably, but the former applies to a community’s environment, whereas the latter applies to a species’ environment.^[24][26][27]

Niche[edit]

Definitions of the niche date back to 1917,^[30] but G. Evelyn Hutchinson made conceptual advances in 1957^[31][32] by introducing a widely adopted definition: «the set of biotic and abiotic conditions in which a species is able to persist and maintain stable population sizes.»^[30]: 519 The ecological niche is a central concept in the ecology of organisms and is sub-divided into the fundamental and the realized niche. The fundamental niche is the set of environmental conditions under which a species is able to persist. The realized niche is the set of environmental plus ecological conditions under which a species persists.^[30][32][33] The Hutchinsonian niche is defined more technically as a «Euclidean hyperspace whose dimensions are defined as environmental variables and whose size is a function of the number of values that the environmental values may assume for which an organism has positive fitness.»^[34]: 71

Biogeographical patterns and range distributions are explained or predicted through knowledge of a species’ traits and niche requirements.^[35] Species have functional traits that are uniquely adapted to the ecological niche. A trait is a measurable property, phenotype, or characteristic of an organism that may influence its survival. Genes play an important role in the interplay of development and environmental expression of traits.^[36] Resident species evolve traits that are fitted to the selection pressures of their local environment. This tends to afford them a competitive advantage and discourages similarly adapted species from having an overlapping geographic range. The competitive exclusion principle states that two species cannot coexist indefinitely by living off the same limiting resource; one will always out-compete the other. When similarly adapted species overlap geographically, closer inspection reveals subtle ecological differences in their habitat or dietary requirements.^[37] Some models and empirical studies, however, suggest that disturbances can stabilize the co-evolution and shared niche occupancy of similar species inhabiting species-rich communities.^[38] The habitat plus the niche is called the ecotope, which is defined as the full range of environmental and biological variables affecting an entire species.^[24]

Niche construction[edit]

Organisms are subject to environmental pressures, but they also modify their habitats. The regulatory feedback between organisms and their environment can affect conditions from local (e.g., a beaver pond) to global scales, over time and even after death, such as decaying logs or silica skeleton deposits from marine organisms.^[39] The process and concept of ecosystem engineering are related to niche construction, but the former relates only to the physical modifications of the habitat whereas the latter also considers the evolutionary implications of physical changes to the environment and the feedback this causes on the process of natural selection. Ecosystem engineers are defined as: «organisms that directly or indirectly modulate the availability of resources to other species, by causing physical state changes in biotic or abiotic materials. In so doing they modify, maintain and create habitats.»^[40]: 373

The ecosystem engineering concept has stimulated a new appreciation for the influence that organisms have on the ecosystem and evolutionary process. The term «niche construction» is more often used in reference to the under-appreciated feedback mechanisms of natural selection imparting forces on the abiotic niche.^[28][41] An example of natural selection through ecosystem engineering occurs in the nests of social insects, including ants, bees, wasps, and termites. There is an emergent homeostasis or homeorhesis in the structure of the nest that regulates, maintains and defends the physiology of the entire colony. Termite mounds, for example, maintain a constant internal temperature through the design of air-conditioning chimneys. The structure of the nests themselves is subject to the forces of natural selection. Moreover, a nest can survive over successive generations, so that progeny inherit both genetic material and a legacy niche that was constructed before their time.^[5][28][29]

Biome[edit]

Biomes are larger units of organization that categorize regions of the Earth’s ecosystems, mainly according to the structure and composition of vegetation.^[42] There are different methods to define the continental boundaries of biomes dominated by different functional types of vegetative communities that are limited in distribution by climate, precipitation, weather, and other environmental variables. Biomes include tropical rainforest, temperate broadleaf and mixed forest, temperate deciduous forest, taiga, tundra, hot desert, and polar desert.^[43] Other researchers have recently categorized other biomes, such as the human and oceanic microbiomes. To a microbe, the human body is a habitat and a landscape.^[44] Microbiomes were discovered largely through advances in molecular genetics, which have revealed a hidden richness of microbial diversity on the planet. The oceanic microbiome plays a significant role in the ecological biogeochemistry of the planet’s oceans.^[45]

Biosphere[edit]

The largest scale of ecological organization is the biosphere: the total sum of ecosystems on the planet. Ecological relationships regulate the flux of energy, nutrients, and climate all the way up to the planetary scale. For example, the dynamic history of the planetary atmosphere’s CO₂ and O₂ composition has been affected by the biogenic flux of gases coming from respiration and photosynthesis, with levels fluctuating over time in relation to the ecology and evolution of plants and animals.^[46] Ecological theory has also been used to explain self-emergent regulatory phenomena at the planetary scale: for example, the Gaia hypothesis is an example of holism applied in ecological theory.^[47] The Gaia hypothesis states that there is an emergent feedback loop generated by the metabolism of living organisms that maintains the core temperature of the Earth and atmospheric conditions within a narrow self-regulating range of tolerance.^[48]

Population ecology[edit]

Population ecology studies the dynamics of species populations and how these populations interact with the wider environment.^[5] A population consists of individuals of the same species that live, interact, and migrate through the same niche and habitat.^[49]

A primary law of population ecology is the Malthusian growth model^[50] which states, «a population will grow (or decline) exponentially as long as the environment experienced by all individuals in the population remains constant.»^[50]: 18 Simplified population models usually starts with four variables: death, birth, immigration, and emigration.

An example of an introductory population model describes a closed population, such as on an island, where immigration and emigration does not take place. Hypotheses are evaluated with reference to a null hypothesis which states that random processes create the observed data. In these island models, the rate of population change is described by:

where N is the total number of individuals in the population, b and d are the per capita rates of birth and death respectively, and r is the per capita rate of population change.^[50][51]

Using these modeling techniques, Malthus’ population principle of growth was later transformed into a model known as the logistic equation by Pierre Verhulst:

where N(t) is the number of individuals measured as biomass density as a function of time, t, r is the maximum per-capita rate of change commonly known as the intrinsic rate of growth, and is the crowding coefficient, which represents the reduction in population growth rate per individual added. The formula states that the rate of change in population size () will grow to approach equilibrium, where (), when the rates of increase and crowding are balanced, . A common, analogous model fixes the equilibrium, as K, which is known as the «carrying capacity.»

Population ecology builds upon these introductory models to further understand demographic processes in real study populations. Commonly used types of data include life history, fecundity, and survivorship, and these are analyzed using mathematical techniques such as matrix algebra. The information is used for managing wildlife stocks and setting harvest quotas.^[51][52] In cases where basic models are insufficient, ecologists may adopt different kinds of statistical methods, such as the Akaike information criterion,^[53] or use models that can become mathematically complex as «several competing hypotheses are simultaneously confronted with the data.»^[54]

Metapopulations and migration[edit]

The concept of metapopulations was defined in 1969^[55] as «a population of populations which go extinct locally and recolonize».^[56]: 105 Metapopulation ecology is another statistical approach that is often used in conservation research.^[57] Metapopulation models simplify the landscape into patches of varying levels of quality,^[58] and metapopulations are linked by the migratory behaviours of organisms. Animal migration is set apart from other kinds of movement because it involves the seasonal departure and return of individuals from a habitat.^[59] Migration is also a population-level phenomenon, as with the migration routes followed by plants as they occupied northern post-glacial environments. Plant ecologists use pollen records that accumulate and stratify in wetlands to reconstruct the timing of plant migration and dispersal relative to historic and contemporary climates. These migration routes involved an expansion of the range as plant populations expanded from one area to another. There is a larger taxonomy of movement, such as commuting, foraging, territorial behavior, stasis, and ranging. Dispersal is usually distinguished from migration because it involves the one-way permanent movement of individuals from their birth population into another population.^[60][61]

In metapopulation terminology, migrating individuals are classed as emigrants (when they leave a region) or immigrants (when they enter a region), and sites are classed either as sources or sinks. A site is a generic term that refers to places where ecologists sample populations, such as ponds or defined sampling areas in a forest. Source patches are productive sites that generate a seasonal supply of juveniles that migrate to other patch locations. Sink patches are unproductive sites that only receive migrants; the population at the site will disappear unless rescued by an adjacent source patch or environmental conditions become more favorable. Metapopulation models examine patch dynamics over time to answer potential questions about spatial and demographic ecology. The ecology of metapopulations is a dynamic process of extinction and colonization. Small patches of lower quality (i.e., sinks) are maintained or rescued by a seasonal influx of new immigrants. A dynamic metapopulation structure evolves from year to year, where some patches are sinks in dry years and are sources when conditions are more favorable. Ecologists use a mixture of computer models and field studies to explain metapopulation structure.^[62][63]

[edit]

Community ecology is the study of the interactions among a collection of species that inhabit the same geographic area. Community ecologists study the determinants of patterns and processes for two or more interacting species. Research in community ecology might measure species diversity in grasslands in relation to soil fertility. It might also include the analysis of predator-prey dynamics, competition among similar plant species, or mutualistic interactions between crabs and corals.

Ecosystem ecology[edit]

Ecosystems may be habitats within biomes that form an integrated whole and a dynamically responsive system having both physical and biological complexes. Ecosystem ecology is the science of determining the fluxes of materials (e.g. carbon, phosphorus) between different pools (e.g., tree biomass, soil organic material). Ecosystem ecologists attempt to determine the underlying causes of these fluxes. Research in ecosystem ecology might measure primary production (g C/m^2) in a wetland in relation to decomposition and consumption rates (g C/m^2/y). This requires an understanding of the community connections between plants (i.e., primary producers) and the decomposers (e.g., fungi and bacteria),^[66]

The underlying concept of an ecosystem can be traced back to 1864 in the published work of George Perkins Marsh («Man and Nature»).^[67][68] Within an ecosystem, organisms are linked to the physical and biological components of their environment to which they are adapted.^[65] Ecosystems are complex adaptive systems where the interaction of life processes form self-organizing patterns across different scales of time and space.^[69] Ecosystems are broadly categorized as terrestrial, freshwater, atmospheric, or marine. Differences stem from the nature of the unique physical environments that shapes the biodiversity within each. A more recent addition to ecosystem ecology are technoecosystems, which are affected by or primarily the result of human activity.^[5]

Food webs[edit]

A food web is the archetypal ecological network. Plants capture solar energy and use it to synthesize simple sugars during photosynthesis. As plants grow, they accumulate nutrients and are eaten by grazing herbivores, and the energy is transferred through a chain of organisms by consumption. The simplified linear feeding pathways that move from a basal trophic species to a top consumer is called the food chain. The larger interlocking pattern of food chains in an ecological community creates a complex food web. Food webs are a type of concept map or a heuristic device that is used to illustrate and study pathways of energy and material flows.^[7][70][71]

Food webs are often limited relative to the real world. Complete empirical measurements are generally restricted to a specific habitat, such as a cave or a pond, and principles gleaned from food web microcosm studies are extrapolated to larger systems.^[72] Feeding relations require extensive investigations into the gut contents of organisms, which can be difficult to decipher, or stable isotopes can be used to trace the flow of nutrient diets and energy through a food web.^[73] Despite these limitations, food webs remain a valuable tool in understanding community ecosystems.^[74]

Food webs exhibit principles of ecological emergence through the nature of trophic relationships: some species have many weak feeding links (e.g., omnivores) while some are more specialized with fewer stronger feeding links (e.g., primary predators). Theoretical and empirical studies identify non-random emergent patterns of few strong and many weak linkages that explain how ecological communities remain stable over time.^[75] Food webs are composed of subgroups where members in a community are linked by strong interactions, and the weak interactions occur between these subgroups. This increases food web stability.^[76] Step by step lines or relations are drawn until a web of life is illustrated.^{[71][77][78][79]}

Trophic levels[edit]

A trophic level (from Greek troph, τροφή, trophē, meaning «food» or «feeding») is «a group of organisms acquiring a considerable majority of its energy from the lower adjacent level (according to ecological pyramids) nearer the abiotic source.»^[80]: 383 Links in food webs primarily connect feeding relations or trophism among species. Biodiversity within ecosystems can be organized into trophic pyramids, in which the vertical dimension represents feeding relations that become further removed from the base of the food chain up toward top predators, and the horizontal dimension represents the abundance or biomass at each level.^[81] When the relative abundance or biomass of each species is sorted into its respective trophic level, they naturally sort into a ‘pyramid of numbers’.^[82]

Species are broadly categorized as autotrophs (or primary producers), heterotrophs (or consumers), and Detritivores (or decomposers). Autotrophs are organisms that produce their own food (production is greater than respiration) by photosynthesis or chemosynthesis. Heterotrophs are organisms that must feed on others for nourishment and energy (respiration exceeds production).^[5] Heterotrophs can be further sub-divided into different functional groups, including primary consumers (strict herbivores), secondary consumers (carnivorous predators that feed exclusively on herbivores), and tertiary consumers (predators that feed on a mix of herbivores and predators).^[83] Omnivores do not fit neatly into a functional category because they eat both plant and animal tissues. It has been suggested that omnivores have a greater functional influence as predators because compared to herbivores, they are relatively inefficient at grazing.^[84]

Trophic levels are part of the holistic or complex systems view of ecosystems.^[85][86] Each trophic level contains unrelated species that are grouped together because they share common ecological functions, giving a macroscopic view of the system.^[87] While the notion of trophic levels provides insight into energy flow and top-down control within food webs, it is troubled by the prevalence of omnivory in real ecosystems. This has led some ecologists to «reiterate that the notion that species clearly aggregate into discrete, homogeneous trophic levels is fiction.»^[88]: 815 Nonetheless, recent studies have shown that real trophic levels do exist, but «above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores.»^[89]: 612

Keystone species[edit]

A keystone species is a species that is connected to a disproportionately large number of other species in the food-web. Keystone species have lower levels of biomass in the trophic pyramid relative to the importance of their role. The many connections that a keystone species holds means that it maintains the organization and structure of entire communities. The loss of a keystone species results in a range of dramatic cascading effects (termed trophic cascades) that alters trophic dynamics, other food web connections, and can cause the extinction of other species.^[90][91] The term keystone species was coined by Robert Paine in 1969 and is a reference to the keystone architectural feature as the removal of a keystone species can result in a community collapse just as the removal of the keystone in an arch can result in the arch’s loss of stability.^[92]

Sea otters (Enhydra lutris) are commonly cited as an example of a keystone species because they limit the density of sea urchins that feed on kelp. If sea otters are removed from the system, the urchins graze until the kelp beds disappear, and this has a dramatic effect on community structure.^[93] Hunting of sea otters, for example, is thought to have led indirectly to the extinction of the Steller’s sea cow (Hydrodamalis gigas).^[94] While the keystone species concept has been used extensively as a conservation tool, it has been criticized for being poorly defined from an operational stance. It is difficult to experimentally determine what species may hold a keystone role in each ecosystem. Furthermore, food web theory suggests that keystone species may not be common, so it is unclear how generally the keystone species model can be applied.^[93][95]

Complexity[edit]

Complexity is understood as a large computational effort needed to piece together numerous interacting parts exceeding the iterative memory capacity of the human mind. Global patterns of biological diversity are complex. This biocomplexity stems from the interplay among ecological processes that operate and influence patterns at different scales that grade into each other, such as transitional areas or ecotones spanning landscapes. Complexity stems from the interplay among levels of biological organization as energy, and matter is integrated into larger units that superimpose onto the smaller parts. «What were wholes on one level become parts on a higher one.»^[96]: 209 Small scale patterns do not necessarily explain large scale phenomena, otherwise captured in the expression (coined by Aristotle) ‘the sum is greater than the parts’.^[97][98][E]

«Complexity in ecology is of at least six distinct types: spatial, temporal, structural, process, behavioral, and geometric.»^[99]: 3 From these principles, ecologists have identified emergent and self-organizing phenomena that operate at different environmental scales of influence, ranging from molecular to planetary, and these require different explanations at each integrative level.^[48][100] Ecological complexity relates to the dynamic resilience of ecosystems that transition to multiple shifting steady-states directed by random fluctuations of history.^[9][101] Long-term ecological studies provide important track records to better understand the complexity and resilience of ecosystems over longer temporal and broader spatial scales. These studies are managed by the International Long Term Ecological Network (LTER).^[102] The longest experiment in existence is the Park Grass Experiment, which was initiated in 1856.^[103] Another example is the Hubbard Brook study, which has been in operation since 1960.^[104]

Holism[edit]

Holism remains a critical part of the theoretical foundation in contemporary ecological studies. Holism addresses the biological organization of life that self-organizes into layers of emergent whole systems that function according to non-reducible properties. This means that higher-order patterns of a whole functional system, such as an ecosystem, cannot be predicted or understood by a simple summation of the parts.^[105] «New properties emerge because the components interact, not because the basic nature of the components is changed.»^[5]: 8

Ecological studies are necessarily holistic as opposed to reductionistic.^{[36][100][106]} Holism has three scientific meanings or uses that identify with ecology: 1) the mechanistic complexity of ecosystems, 2) the practical description of patterns in quantitative reductionist terms where correlations may be identified but nothing is understood about the causal relations without reference to the whole system, which leads to 3) a metaphysical hierarchy whereby the causal relations of larger systems are understood without reference to the smaller parts. Scientific holism differs from mysticism that has appropriated the same term. An example of metaphysical holism is identified in the trend of increased exterior thickness in shells of different species. The reason for a thickness increase can be understood through reference to principles of natural selection via predation without the need to reference or understand the biomolecular properties of the exterior shells.^[107]

Relation to evolution[edit]

Ecology and evolutionary biology are considered sister disciplines of the life sciences. Natural selection, life history, development, adaptation, populations, and inheritance are examples of concepts that thread equally into ecological and evolutionary theory. Morphological, behavioural, and genetic traits, for example, can be mapped onto evolutionary trees to study the historical development of a species in relation to their functions and roles in different ecological circumstances. In this framework, the analytical tools of ecologists and evolutionists overlap as they organize, classify, and investigate life through common systematic principles, such as phylogenetics or the Linnaean system of taxonomy.^[108] The two disciplines often appear together, such as in the title of the journal Trends in Ecology and Evolution.^[109] There is no sharp boundary separating ecology from evolution, and they differ more in their areas of applied focus. Both disciplines discover and explain emergent and unique properties and processes operating across different spatial or temporal scales of organization.^[36][48] While the boundary between ecology and evolution is not always clear, ecologists study the abiotic and biotic factors that influence evolutionary processes,^[110][111] and evolution can be rapid, occurring on ecological timescales as short as one generation.^[112]

Behavioural ecology[edit]

All organisms can exhibit behaviours. Even plants express complex behaviour, including memory and communication.^[114] Behavioural ecology is the study of an organism’s behaviour in its environment and its ecological and evolutionary implications. Ethology is the study of observable movement or behaviour in animals. This could include investigations of motile sperm of plants, mobile phytoplankton, zooplankton swimming toward the female egg, the cultivation of fungi by weevils, the mating dance of a salamander, or social gatherings of amoeba.^{[115][116][117][118][119]}

Adaptation is the central unifying concept in behavioural ecology.^[120] Behaviours can be recorded as traits and inherited in much the same way that eye and hair colour can. Behaviours can evolve by means of natural selection as adaptive traits conferring functional utilities that increases reproductive fitness.^[121][122]

Predator-prey interactions are an introductory concept into food-web studies as well as behavioural ecology.^[124] Prey species can exhibit different kinds of behavioural adaptations to predators, such as avoid, flee, or defend. Many prey species are faced with multiple predators that differ in the degree of danger posed. To be adapted to their environment and face predatory threats, organisms must balance their energy budgets as they invest in different aspects of their life history, such as growth, feeding, mating, socializing, or modifying their habitat. Hypotheses posited in behavioural ecology are generally based on adaptive principles of conservation, optimization, or efficiency.^{[33][110][125]} For example, «[t]he threat-sensitive predator avoidance hypothesis predicts that prey should assess the degree of threat posed by different predators and match their behaviour according to current levels of risk»^[126] or «[t]he optimal flight initiation distance occurs where expected postencounter fitness is maximized, which depends on the prey’s initial fitness, benefits obtainable by not fleeing, energetic escape costs, and expected fitness loss due to predation risk.»^[127]

Elaborate sexual displays and posturing are encountered in the behavioural ecology of animals. The birds-of-paradise, for example, sing and display elaborate ornaments during courtship. These displays serve a dual purpose of signalling healthy or well-adapted individuals and desirable genes. The displays are driven by sexual selection as an advertisement of quality of traits among suitors.^[128]

Cognitive ecology[edit]

Cognitive ecology integrates theory and observations from evolutionary ecology and neurobiology, primarily cognitive science, in order to understand the effect that animal interaction with their habitat has on their cognitive systems and how those systems restrict behavior within an ecological and evolutionary framework.^[129] «Until recently, however, cognitive scientists have not paid sufficient attention to the fundamental fact that cognitive traits evolved under particular natural settings. With consideration of the selection pressure on cognition, cognitive ecology can contribute intellectual coherence to the multidisciplinary study of cognition.»^[130][131] As a study involving the ‘coupling’ or interactions between organism and environment, cognitive ecology is closely related to enactivism,^[129] a field based upon the view that «…we must see the organism and environment as bound together in reciprocal specification and selection…».^[132]

[edit]

Social-ecological behaviours are notable in the social insects, slime moulds, social spiders, human society, and naked mole-rats where eusocialism has evolved. Social behaviours include reciprocally beneficial behaviours among kin and nest mates^{[117][122][133]} and evolve from kin and group selection. Kin selection explains altruism through genetic relationships, whereby an altruistic behaviour leading to death is rewarded by the survival of genetic copies distributed among surviving relatives. The social insects, including ants, bees, and wasps are most famously studied for this type of relationship because the male drones are clones that share the same genetic make-up as every other male in the colony.^[122] In contrast, group selectionists find examples of altruism among non-genetic relatives and explain this through selection acting on the group; whereby, it becomes selectively advantageous for groups if their members express altruistic behaviours to one another. Groups with predominantly altruistic members survive better than groups with predominantly selfish members.^[122][134]

Coevolution[edit]

Ecological interactions can be classified broadly into a host and an associate relationship. A host is any entity that harbours another that is called the associate.^[135] Relationships between species that are mutually or reciprocally beneficial are called mutualisms. Examples of mutualism include fungus-growing ants employing agricultural symbiosis, bacteria living in the guts of insects and other organisms, the fig wasp and yucca moth pollination complex, lichens with fungi and photosynthetic algae, and corals with photosynthetic algae.^[136][137] If there is a physical connection between host and associate, the relationship is called symbiosis. Approximately 60% of all plants, for example, have a symbiotic relationship with arbuscular mycorrhizal fungi living in their roots forming an exchange network of carbohydrates for mineral nutrients.^[138]

Indirect mutualisms occur where the organisms live apart. For example, trees living in the equatorial regions of the planet supply oxygen into the atmosphere that sustains species living in distant polar regions of the planet. This relationship is called commensalism because many others receive the benefits of clean air at no cost or harm to trees supplying the oxygen.^[5][139] If the associate benefits while the host suffers, the relationship is called parasitism. Although parasites impose a cost to their host (e.g., via damage to their reproductive organs or propagules, denying the services of a beneficial partner), their net effect on host fitness is not necessarily negative and, thus, becomes difficult to forecast.^[140][141] Co-evolution is also driven by competition among species or among members of the same species under the banner of reciprocal antagonism, such as grasses competing for growth space. The Red Queen Hypothesis, for example, posits that parasites track down and specialize on the locally common genetic defense systems of its host that drives the evolution of sexual reproduction to diversify the genetic constituency of populations responding to the antagonistic pressure.^[142][143]

Biogeography[edit]

Biogeography (an amalgamation of biology and geography) is the comparative study of the geographic distribution of organisms and the corresponding evolution of their traits in space and time.^[144] The Journal of Biogeography was established in 1974.^[145] Biogeography and ecology share many of their disciplinary roots. For example, the theory of island biogeography, published by the Robert MacArthur and Edward O. Wilson in 1967^[146] is considered one of the fundamentals of ecological theory.^[147]

Biogeography has a long history in the natural sciences concerning the spatial distribution of plants and animals. Ecology and evolution provide the explanatory context for biogeographical studies.^[144] Biogeographical patterns result from ecological processes that influence range distributions, such as migration and dispersal.^[147] and from historical processes that split populations or species into different areas. The biogeographic processes that result in the natural splitting of species explain much of the modern distribution of the Earth’s biota. The splitting of lineages in a species is called vicariance biogeography and it is a sub-discipline of biogeography.^[148] There are also practical applications in the field of biogeography concerning ecological systems and processes. For example, the range and distribution of biodiversity and invasive species responding to climate change is a serious concern and active area of research in the context of global warming.^[149][150]

r/K selection theory[edit]

A population ecology concept is r/K selection theory,^[D] one of the first predictive models in ecology used to explain life-history evolution. The premise behind the r/K selection model is that natural selection pressures change according to population density. For example, when an island is first colonized, density of individuals is low. The initial increase in population size is not limited by competition, leaving an abundance of available resources for rapid population growth. These early phases of population growth experience density-independent forces of natural selection, which is called r-selection. As the population becomes more crowded, it approaches the island’s carrying capacity, thus forcing individuals to compete more heavily for fewer available resources. Under crowded conditions, the population experiences density-dependent forces of natural selection, called K-selection.^[151]

In the r/K-selection model, the first variable r is the intrinsic rate of natural increase in population size and the second variable K is the carrying capacity of a population.^[33] Different species evolve different life-history strategies spanning a continuum between these two selective forces. An r-selected species is one that has high birth rates, low levels of parental investment, and high rates of mortality before individuals reach maturity. Evolution favours high rates of fecundity in r-selected species. Many kinds of insects and invasive species exhibit r-selected characteristics. In contrast, a K-selected species has low rates of fecundity, high levels of parental investment in the young, and low rates of mortality as individuals mature. Humans and elephants are examples of species exhibiting K-selected characteristics, including longevity and efficiency in the conversion of more resources into fewer offspring.^[146][152]

Molecular ecology[edit]

The important relationship between ecology and genetic inheritance predates modern techniques for molecular analysis. Molecular ecological research became more feasible with the development of rapid and accessible genetic technologies, such as the polymerase chain reaction (PCR). The rise of molecular technologies and the influx of research questions into this new ecological field resulted in the publication Molecular Ecology in 1992.^[153] Molecular ecology uses various analytical techniques to study genes in an evolutionary and ecological context. In 1994, John Avise also played a leading role in this area of science with the publication of his book, Molecular Markers, Natural History and Evolution.^[154] Newer technologies opened a wave of genetic analysis into organisms once difficult to study from an ecological or evolutionary standpoint, such as bacteria, fungi, and nematodes. Molecular ecology engendered a new research paradigm for investigating ecological questions considered otherwise intractable. Molecular investigations revealed previously obscured details in the tiny intricacies of nature and improved resolution into probing questions about behavioural and biogeographical ecology.^[154] For example, molecular ecology revealed promiscuous sexual behaviour and multiple male partners in tree swallows previously thought to be socially monogamous.^[155] In a biogeographical context, the marriage between genetics, ecology, and evolution resulted in a new sub-discipline called phylogeography.^[156]

Human ecology[edit]

Ecology is as much a biological science as it is a human science.^[5] Human ecology is an interdisciplinary investigation into the ecology of our species. «Human ecology may be defined: (1) from a bioecological standpoint as the study of man as the ecological dominant in plant and animal communities and systems; (2) from a bioecological standpoint as simply another animal affecting and being affected by his physical environment; and (3) as a human being, somehow different from animal life in general, interacting with physical and modified environments in a distinctive and creative way. A truly interdisciplinary human ecology will most likely address itself to all three.»^[158]: 3 The term was formally introduced in 1921, but many sociologists, geographers, psychologists, and other disciplines were interested in human relations to natural systems centuries prior, especially in the late 19th century.^[158][159]

The ecological complexities human beings are facing through the technological transformation of the planetary biome has brought on the Anthropocene. The unique set of circumstances has generated the need for a new unifying science called coupled human and natural systems that builds upon, but moves beyond the field of human ecology.^[105] Ecosystems tie into human societies through the critical and all-encompassing life-supporting functions they sustain. In recognition of these functions and the incapability of traditional economic valuation methods to see the value in ecosystems, there has been a surge of interest in social-natural capital, which provides the means to put a value on the stock and use of information and materials stemming from ecosystem goods and services. Ecosystems produce, regulate, maintain, and supply services of critical necessity and beneficial to human health (cognitive and physiological), economies, and they even provide an information or reference function as a living library giving opportunities for science and cognitive development in children engaged in the complexity of the natural world. Ecosystems relate importantly to human ecology as they are the ultimate base foundation of global economics as every commodity, and the capacity for exchange ultimately stems from the ecosystems on Earth.^{[105][160][161][162]}

Ecology is an employed science of restoration, repairing disturbed sites through human intervention, in natural resource management, and in environmental impact assessments. Edward O. Wilson predicted in 1992 that the 21st century «will be the era of restoration in ecology».^[164] Ecological science has boomed in the industrial investment of restoring ecosystems and their processes in abandoned sites after disturbance. Natural resource managers, in forestry, for example, employ ecologists to develop, adapt, and implement ecosystem based methods into the planning, operation, and restoration phases of land-use. Another example of conservation is seen on the east coast of the United States in Boston, MA. The city of Boston implemented the Wetland Ordinance,^[165] improving the stability of their wetland environments by implementing soil amendments that will improve groundwater storage and flow, and trimming or removal of vegetation that could cause harm to water quality.^{[citation needed]} Ecological science is used in the methods of sustainable harvesting, disease, and fire outbreak management, in fisheries stock management, for integrating land-use with protected areas and communities, and conservation in complex geo-political landscapes.^{[22][163][166][167]}

Relation to the environment[edit]

The environment of ecosystems includes both physical parameters and biotic attributes. It is dynamically interlinked and contains resources for organisms at any time throughout their life cycle.^[5][168] Like ecology, the term environment has different conceptual meanings and overlaps with the concept of nature. Environment «includes the physical world, the social world of human relations and the built world of human creation.»^[169]: 62 The physical environment is external to the level of biological organization under investigation, including abiotic factors such as temperature, radiation, light, chemistry, climate and geology. The biotic environment includes genes, cells, organisms, members of the same species (conspecifics) and other species that share a habitat.^[170]

The distinction between external and internal environments, however, is an abstraction parsing life and environment into units or facts that are inseparable in reality. There is an interpenetration of cause and effect between the environment and life. The laws of thermodynamics, for example, apply to ecology by means of its physical state. With an understanding of metabolic and thermodynamic principles, a complete accounting of energy and material flow can be traced through an ecosystem. In this way, the environmental and ecological relations are studied through reference to conceptually manageable and isolated material parts. After the effective environmental components are understood through reference to their causes; however, they conceptually link back together as an integrated whole, or holocoenotic system as it was once called. This is known as the dialectical approach to ecology. The dialectical approach examines the parts but integrates the organism and the environment into a dynamic whole (or umwelt). Change in one ecological or environmental factor can concurrently affect the dynamic state of an entire ecosystem.^[36][171]

Disturbance and resilience[edit]

Ecosystems are regularly confronted with natural environmental variations and disturbances over time and geographic space. A disturbance is any process that removes biomass from a community, such as a fire, flood, drought, or predation.^[172] Disturbances occur over vastly different ranges in terms of magnitudes as well as distances and time periods,^[173] and are both the cause and product of natural fluctuations in death rates, species assemblages, and biomass densities within an ecological community. These disturbances create places of renewal where new directions emerge from the patchwork of natural experimentation and opportunity.^{[172][174][175]} Ecological resilience is a cornerstone theory in ecosystem management. Biodiversity fuels the resilience of ecosystems acting as a kind of regenerative insurance.^[175]

Metabolism and the early atmosphere[edit]

The Earth was formed approximately 4.5 billion years ago.^[177] As it cooled and a crust and oceans formed, its atmosphere transformed from being dominated by hydrogen to one composed mostly of methane and ammonia. Over the next billion years, the metabolic activity of life transformed the atmosphere into a mixture of carbon dioxide, nitrogen, and water vapor. These gases changed the way that light from the sun hit the Earth’s surface and greenhouse effects trapped heat. There were untapped sources of free energy within the mixture of reducing and oxidizing gasses that set the stage for primitive ecosystems to evolve and, in turn, the atmosphere also evolved.^[178]

Throughout history, the Earth’s atmosphere and biogeochemical cycles have been in a dynamic equilibrium with planetary ecosystems. The history is characterized by periods of significant transformation followed by millions of years of stability.^[179] The evolution of the earliest organisms, likely anaerobic methanogen microbes, started the process by converting atmospheric hydrogen into methane (4H₂ + CO₂ → CH₄ + 2H₂O). Anoxygenic photosynthesis reduced hydrogen concentrations and increased atmospheric methane, by converting hydrogen sulfide into water or other sulfur compounds (for example, 2H₂S + CO₂ + hv → CH₂O + H₂O + 2S). Early forms of fermentation also increased levels of atmospheric methane. The transition to an oxygen-dominant atmosphere (the Great Oxidation) did not begin until approximately 2.4–2.3 billion years ago, but photosynthetic processes started 0.3 to 1 billion years prior.^[179][180]

Radiation: heat, temperature and light[edit]

The biology of life operates within a certain range of temperatures. Heat is a form of energy that regulates temperature. Heat affects growth rates, activity, behaviour, and primary production. Temperature is largely dependent on the incidence of solar radiation. The latitudinal and longitudinal spatial variation of temperature greatly affects climates and consequently the distribution of biodiversity and levels of primary production in different ecosystems or biomes across the planet. Heat and temperature relate importantly to metabolic activity. Poikilotherms, for example, have a body temperature that is largely regulated and dependent on the temperature of the external environment. In contrast, homeotherms regulate their internal body temperature by expending metabolic energy.^{[110][111][171]}

There is a relationship between light, primary production, and ecological energy budgets. Sunlight is the primary input of energy into the planet’s ecosystems. Light is composed of electromagnetic energy of different wavelengths. Radiant energy from the sun generates heat, provides photons of light measured as active energy in the chemical reactions of life, and also acts as a catalyst for genetic mutation.^{[110][111][171]} Plants, algae, and some bacteria absorb light and assimilate the energy through photosynthesis. Organisms capable of assimilating energy by photosynthesis or through inorganic fixation of H₂S are autotrophs. Autotrophs—responsible for primary production—assimilate light energy which becomes metabolically stored as potential energy in the form of biochemical enthalpic bonds.^{[110][111][171]}

Physical environments[edit]

Water[edit]

Diffusion of carbon dioxide and oxygen is approximately 10,000 times slower in water than in air. When soils are flooded, they quickly lose oxygen, becoming hypoxic (an environment with O₂ concentration below 2 mg/liter) and eventually completely anoxic where anaerobic bacteria thrive among the roots. Water also influences the intensity and spectral composition of light as it reflects off the water surface and submerged particles.^[181] Aquatic plants exhibit a wide variety of morphological and physiological adaptations that allow them to survive, compete, and diversify in these environments. For example, their roots and stems contain large air spaces (aerenchyma) that regulate the efficient transportation of gases (for example, CO₂ and O₂) used in respiration and photosynthesis. Salt water plants (halophytes) have additional specialized adaptations, such as the development of special organs for shedding salt and osmoregulating their internal salt (NaCl) concentrations, to live in estuarine, brackish, or oceanic environments. Anaerobic soil microorganisms in aquatic environments use nitrate, manganese ions, ferric ions, sulfate, carbon dioxide, and some organic compounds; other microorganisms are facultative anaerobes and use oxygen during respiration when the soil becomes drier. The activity of soil microorganisms and the chemistry of the water reduces the oxidation-reduction potentials of the water. Carbon dioxide, for example, is reduced to methane (CH₄) by methanogenic bacteria.^[181] The physiology of fish is also specially adapted to compensate for environmental salt levels through osmoregulation. Their gills form electrochemical gradients that mediate salt excretion in salt water and uptake in fresh water.^[182]

Gravity[edit]

The shape and energy of the land are significantly affected by gravitational forces. On a large scale, the distribution of gravitational forces on the earth is uneven and influences the shape and movement of tectonic plates as well as influencing geomorphic processes such as orogeny and erosion. These forces govern many of the geophysical properties and distributions of ecological biomes across the Earth. On the organismal scale, gravitational forces provide directional cues for plant and fungal growth (gravitropism), orientation cues for animal migrations, and influence the biomechanics and size of animals.^[110] Ecological traits, such as allocation of biomass in trees during growth are subject to mechanical failure as gravitational forces influence the position and structure of branches and leaves.^[183] The cardiovascular systems of animals are functionally adapted to overcome the pressure and gravitational forces that change according to the features of organisms (e.g., height, size, shape), their behaviour (e.g., diving, running, flying), and the habitat occupied (e.g., water, hot deserts, cold tundra).^[184]

Pressure[edit]

Climatic and osmotic pressure places physiological constraints on organisms, especially those that fly and respire at high altitudes, or dive to deep ocean depths.^[185] These constraints influence vertical limits of ecosystems in the biosphere, as organisms are physiologically sensitive and adapted to atmospheric and osmotic water pressure differences.^[110] For example, oxygen levels decrease with decreasing pressure and are a limiting factor for life at higher altitudes.^[186] Water transportation by plants is another important ecophysiological process affected by osmotic pressure gradients.^{[187][188][189]} Water pressure in the depths of oceans requires that organisms adapt to these conditions. For example, diving animals such as whales, dolphins, and seals are specially adapted to deal with changes in sound due to water pressure differences.^[190] Differences between hagfish species provide another example of adaptation to deep-sea pressure through specialized protein adaptations.^[191]

Wind and turbulence[edit]

Turbulent forces in air and water affect the environment and ecosystem distribution, form, and dynamics. On a planetary scale, ecosystems are affected by circulation patterns in the global trade winds. Wind power and the turbulent forces it creates can influence heat, nutrient, and biochemical profiles of ecosystems.^[110] For example, wind running over the surface of a lake creates turbulence, mixing the water column and influencing the environmental profile to create thermally layered zones, affecting how fish, algae, and other parts of the aquatic ecosystem are structured.^[194][195] Wind speed and turbulence also influence evapotranspiration rates and energy budgets in plants and animals.^[181][196] Wind speed, temperature and moisture content can vary as winds travel across different land features and elevations. For example, the westerlies come into contact with the coastal and interior mountains of western North America to produce a rain shadow on the leeward side of the mountain. The air expands and moisture condenses as the winds increase in elevation; this is called orographic lift and can cause precipitation. This environmental process produces spatial divisions in biodiversity, as species adapted to wetter conditions are range-restricted to the coastal mountain valleys and unable to migrate across the xeric ecosystems (e.g., of the Columbia Basin in western North America) to intermix with sister lineages that are segregated to the interior mountain systems.^[197][198]

Fire[edit]

Plants convert carbon dioxide into biomass and emit oxygen into the atmosphere. By approximately 350 million years ago (the end of the Devonian period), photosynthesis had brought the concentration of atmospheric oxygen above 17%, which allowed combustion to occur.^[199] Fire releases CO₂ and converts fuel into ash and tar. Fire is a significant ecological parameter that raises many issues pertaining to its control and suppression.^[200] While the issue of fire in relation to ecology and plants has been recognized for a long time,^[201] Charles Cooper brought attention to the issue of forest fires in relation to the ecology of forest fire suppression and management in the 1960s.^[202][203]

Native North Americans were among the first to influence fire regimes by controlling their spread near their homes or by lighting fires to stimulate the production of herbaceous foods and basketry materials.^[204] Fire creates a heterogeneous ecosystem age and canopy structure, and the altered soil nutrient supply and cleared canopy structure opens new ecological niches for seedling establishment.^[205][206] Most ecosystems are adapted to natural fire cycles. Plants, for example, are equipped with a variety of adaptations to deal with forest fires. Some species (e.g., Pinus halepensis) cannot germinate until after their seeds have lived through a fire or been exposed to certain compounds from smoke. Environmentally triggered germination of seeds is called serotiny.^[207][208] Fire plays a major role in the persistence and resilience of ecosystems.^[174]

Soils[edit]

Soil is the living top layer of mineral and organic dirt that covers the surface of the planet. It is the chief organizing centre of most ecosystem functions, and it is of critical importance in agricultural science and ecology. The decomposition of dead organic matter (for example, leaves on the forest floor), results in soils containing minerals and nutrients that feed into plant production. The whole of the planet’s soil ecosystems is called the pedosphere where a large biomass of the Earth’s biodiversity organizes into trophic levels. Invertebrates that feed and shred larger leaves, for example, create smaller bits for smaller organisms in the feeding chain. Collectively, these organisms are the detritivores that regulate soil formation.^[209][210] Tree roots, fungi, bacteria, worms, ants, beetles, centipedes, spiders, mammals, birds, reptiles, amphibians, and other less familiar creatures all work to create the trophic web of life in soil ecosystems. Soils form composite phenotypes where inorganic matter is enveloped into the physiology of a whole community. As organisms feed and migrate through soils they physically displace materials, an ecological process called bioturbation. This aerates soils and stimulates heterotrophic growth and production. Soil microorganisms are influenced by and are fed back into the trophic dynamics of the ecosystem. No single axis of causality can be discerned to segregate the biological from geomorphological systems in soils.^[211][212] Paleoecological studies of soils places the origin for bioturbation to a time before the Cambrian period. Other events, such as the evolution of trees and the colonization of land in the Devonian period played a significant role in the early development of ecological trophism in soils.^{[210][213][214]}

Biogeochemistry and climate[edit]

Ecologists study and measure nutrient budgets to understand how these materials are regulated, flow, and recycled through the environment.^{[110][111][171]} This research has led to an understanding that there is global feedback between ecosystems and the physical parameters of this planet, including minerals, soil, pH, ions, water, and atmospheric gases. Six major elements (hydrogen, carbon, nitrogen, oxygen, sulfur, and phosphorus; H, C, N, O, S, and P) form the constitution of all biological macromolecules and feed into the Earth’s geochemical processes. From the smallest scale of biology, the combined effect of billions upon billions of ecological processes amplify and ultimately regulate the biogeochemical cycles of the Earth. Understanding the relations and cycles mediated between these elements and their ecological pathways has significant bearing toward understanding global biogeochemistry.^[215]

The ecology of global carbon budgets gives one example of the linkage between biodiversity and biogeochemistry. It is estimated that the Earth’s oceans hold 40,000 gigatonnes (Gt) of carbon, that vegetation and soil hold 2070 Gt, and that fossil fuel emissions are 6.3 Gt carbon per year.^[216] There have been major restructurings in these global carbon budgets during the Earth’s history, regulated to a large extent by the ecology of the land. For example, through the early-mid Eocene volcanic outgassing, the oxidation of methane stored in wetlands, and seafloor gases increased atmospheric CO₂ (carbon dioxide) concentrations to levels as high as 3500 ppm.^[217]

In the Oligocene, from twenty-five to thirty-two million years ago, there was another significant restructuring of the global carbon cycle as grasses evolved a new mechanism of photosynthesis, C₄ photosynthesis, and expanded their ranges. This new pathway evolved in response to the drop in atmospheric CO₂ concentrations below 550 ppm.^[218] The relative abundance and distribution of biodiversity alters the dynamics between organisms and their environment such that ecosystems can be both cause and effect in relation to climate change. Human-driven modifications to the planet’s ecosystems (e.g., disturbance, biodiversity loss, agriculture) contributes to rising atmospheric greenhouse gas levels. Transformation of the global carbon cycle in the next century is projected to raise planetary temperatures, lead to more extreme fluctuations in weather, alter species distributions, and increase extinction rates. The effect of global warming is already being registered in melting glaciers, melting mountain ice caps, and rising sea levels. Consequently, species distributions are changing along waterfronts and in continental areas where migration patterns and breeding grounds are tracking the prevailing shifts in climate. Large sections of permafrost are also melting to create a new mosaic of flooded areas having increased rates of soil decomposition activity that raises methane (CH₄) emissions. There is concern over increases in atmospheric methane in the context of the global carbon cycle, because methane is a greenhouse gas that is 23 times more effective at absorbing long-wave radiation than CO₂ on a 100-year time scale.^[219] Hence, there is a relationship between global warming, decomposition and respiration in soils and wetlands producing significant climate feedbacks and globally altered biogeochemical cycles.^{[105][220][221][222][223][224]}

History[edit]

Early beginnings[edit]

Ecology has a complex origin, due in large part to its interdisciplinary nature.^[226] Ancient Greek philosophers such as Hippocrates and Aristotle were among the first to record observations on natural history. However, they viewed life in terms of essentialism, where species were conceptualized as static unchanging things while varieties were seen as aberrations of an idealized type. This contrasts against the modern understanding of ecological theory where varieties are viewed as the real phenomena of interest and having a role in the origins of adaptations by means of natural selection.^{[5][227][228]} Early conceptions of ecology, such as a balance and regulation in nature can be traced to Herodotus (died c. 425 BC), who described one of the earliest accounts of mutualism in his observation of «natural dentistry». Basking Nile crocodiles, he noted, would open their mouths to give sandpipers safe access to pluck leeches out, giving nutrition to the sandpiper and oral hygiene for the crocodile.^[226] Aristotle was an early influence on the philosophical development of ecology. He and his student Theophrastus made extensive observations on plant and animal migrations, biogeography, physiology, and their behavior, giving an early analogue to the modern concept of an ecological niche.^[229][230]

Ecological concepts such as food chains, population regulation, and productivity were first developed in the 1700s, through the published works of microscopist Antoni van Leeuwenhoek (1632–1723) and botanist Richard Bradley (1688?–1732).^[5] Biogeographer Alexander von Humboldt (1769–1859) was an early pioneer in ecological thinking and was among the first to recognize ecological gradients, where species are replaced or altered in form along environmental gradients, such as a cline forming along a rise in elevation. Humboldt drew inspiration from Isaac Newton, as he developed a form of «terrestrial physics». In Newtonian fashion, he brought a scientific exactitude for measurement into natural history and even alluded to concepts that are the foundation of a modern ecological law on species-to-area relationships.^{[232][233][234]} Natural historians, such as Humboldt, James Hutton, and Jean-Baptiste Lamarck (among others) laid the foundations of the modern ecological sciences.^[235] The term «ecology» (German: Oekologie, Ökologie) was coined by Ernst Haeckel in his book Generelle Morphologie der Organismen (1866).^[236] Haeckel was a zoologist, artist, writer, and later in life a professor of comparative anatomy.^[225][237]

Opinions differ on who was the founder of modern ecological theory. Some mark Haeckel’s definition as the beginning;^[238] others say it was Eugenius Warming with the writing of Oecology of Plants: An Introduction to the Study of Plant Communities (1895),^[239] or Carl Linnaeus’ principles on the economy of nature that matured in the early 18th century.^[240][241] Linnaeus founded an early branch of ecology that he called the economy of nature.^[240] His works influenced Charles Darwin, who adopted Linnaeus’ phrase on the economy or polity of nature in The Origin of Species.^[225] Linnaeus was the first to frame the balance of nature as a testable hypothesis. Haeckel, who admired Darwin’s work, defined ecology in reference to the economy of nature, which has led some to question whether ecology and the economy of nature are synonymous.^[241]

From Aristotle until Darwin, the natural world was predominantly considered static and unchanging. Prior to The Origin of Species, there was little appreciation or understanding of the dynamic and reciprocal relations between organisms, their adaptations, and the environment.^[227] An exception is the 1789 publication Natural History of Selborne by Gilbert White (1720–1793), considered by some to be one of the earliest texts on ecology.^[244] While Charles Darwin is mainly noted for his treatise on evolution,^[245] he was one of the founders of soil ecology,^[246] and he made note of the first ecological experiment in The Origin of Species.^[242] Evolutionary theory changed the way that researchers approached the ecological sciences.^[247]

Since 1900[edit]

Modern ecology is a young science that first attracted substantial scientific attention toward the end of the 19th century (around the same time that evolutionary studies were gaining scientific interest). The scientist Ellen Swallow Richards adopted the term «oekology» (which eventually morphed into home economics) in the U.S. as early as 1892.^[248]

In the early 20th century, ecology transitioned from a more descriptive form of natural history to a more analytical form of scientific natural history.^[232][235] Frederic Clements published the first American ecology book in 1905,^[249] presenting the idea of plant communities as a superorganism. This publication launched a debate between ecological holism and individualism that lasted until the 1970s. Clements’ superorganism concept proposed that ecosystems progress through regular and determined stages of seral development that are analogous to the developmental stages of an organism. The Clementsian paradigm was challenged by Henry Gleason,^[250] who stated that ecological communities develop from the unique and coincidental association of individual organisms. This perceptual shift placed the focus back onto the life histories of individual organisms and how this relates to the development of community associations.^[251]

The Clementsian superorganism theory was an overextended application of an idealistic form of holism.^[36][107] The term «holism» was coined in 1926 by Jan Christiaan Smuts, a South African general and polarizing historical figure who was inspired by Clements’ superorganism concept.^[252][C] Around the same time, Charles Elton pioneered the concept of food chains in his classical book Animal Ecology.^[82] Elton^[82] defined ecological relations using concepts of food chains, food cycles, and food size, and described numerical relations among different functional groups and their relative abundance. Elton’s ‘food cycle’ was replaced by ‘food web’ in a subsequent ecological text.^[253] Alfred J. Lotka brought in many theoretical concepts applying thermodynamic principles to ecology.

In 1942, Raymond Lindeman wrote a landmark paper on the trophic dynamics of ecology, which was published posthumously after initially being rejected for its theoretical emphasis. Trophic dynamics became the foundation for much of the work to follow on energy and material flow through ecosystems. Robert MacArthur advanced mathematical theory, predictions, and tests in ecology in the 1950s, which inspired a resurgent school of theoretical mathematical ecologists.^{[235][254][255]} Ecology also has developed through contributions from other nations, including Russia’s Vladimir Vernadsky and his founding of the biosphere concept in the 1920s^[256] and Japan’s Kinji Imanishi and his concepts of harmony in nature and habitat segregation in the 1950s.^[257] Scientific recognition of contributions to ecology from non-English-speaking cultures is hampered by language and translation barriers.^[256]

Ecology surged in popular and scientific interest during the 1960–1970s environmental movement. There are strong historical and scientific ties between ecology, environmental management, and protection.^[235] The historical emphasis and poetic naturalistic writings advocating the protection of wild places by notable ecologists in the history of conservation biology, such as Aldo Leopold and Arthur Tansley, have been seen as far removed from urban centres where, it is claimed, the concentration of pollution and environmental degradation is located.^[235][259] Palamar (2008)^[259] notes an overshadowing by mainstream environmentalism of pioneering women in the early 1900s who fought for urban health ecology (then called euthenics)^[248] and brought about changes in environmental legislation. Women such as Ellen Swallow Richards and Julia Lathrop, among others, were precursors to the more popularized environmental movements after the 1950s.

In 1962, marine biologist and ecologist Rachel Carson’s book Silent Spring helped to mobilize the environmental movement by alerting the public to toxic pesticides, such as DDT, bioaccumulating in the environment. Carson used ecological science to link the release of environmental toxins to human and ecosystem health. Since then, ecologists have worked to bridge their understanding of the degradation of the planet’s ecosystems with environmental politics, law, restoration, and natural resources management.^{[22][235][259][260]}

See also[edit]

Lists

Notes[edit]

References[edit]

External links[edit]

• Ecology (Stanford Encyclopedia of Philosophy)
• The Nature Education Knowledge Project: Ecology

Ecology or ecological science, is the scientific study of the distribution and abundance of living organisms and how these properties are affected by interactions between the organisms and their environment. The environment of an organism includes both the physical properties, which can be described as the sum of local abiotic factors like climate and geology, as well as the other organisms that share its habitat.

Ecology may be more simply defined as the relationship between living organisms and their abiotic and biotic environment or as «the study of the structure and function of nature» (Odum 1971). In this later case, structure includes the distribution patterns and abundance of organisms, and function includes the interactions of populations, including competition, predation, symbiosis, and nutrient and energy cycles.

The term ecology (oekologie) was coined in 1866 by the German biologist Ernst Haeckel. The word is derived from the Greek oikos («household,» «home,» or «place to live») and logos («study»)—therefore, «ecology» means the «study of the household of nature.» The name is derived from the same root word as economics (management of the household), and thus ecology is sometimes considered the economics of nature, or, as expressed by Ernst Haeckel, «the body of knowledge concerning the economy of nature» (Smith 1996).

The interactions between living organisms and their abiotic and biotic environments, the focus of ecology, generally convey an overall sense of unity and harmony in nature. See for instance, species interactions. On the other hand, the history of the science itself has often revealed conflicts, schisms, and opposing camps, as ecologists took different approaches and often failed to meet on common ground.

Scope

Ecology is usually considered a branch of biology, the general science that studies living and once-living organisms. Organisms can be studied at many different levels, from proteins and nucleic acids (in biochemistry and molecular biology), to cells (in cellular biology), to multicellular systems (in physiology and anatomy, to individuals (in botany, zoology, and other similar disciplines), and finally at the level of populations, communities, and ecosystems, and to the biosphere as a whole. These latter strata, from populations to the biosphere, are the primary subjects of ecological inquiries.

Ecology is a multi-disciplinary science. Because of its focus on the higher levels of the organization of life on earth and on the interrelations between organisms and their environment, ecology draws heavily on many other branches of science, especially geology and geography, meteorology, pedology, chemistry, and physics. Thus, ecology is said to be a holistic science, one that overarches older disciplines, such as biology, which in this view become sub-disciplines contributing to ecological knowledge.

Agriculture, fisheries, forestry, medicine, and urban development are among human activities that would fall within Krebs’ (1972: 4) explanation of his definition of ecology: «where organisms are found, how many occur there, and why.»

The term ecology is sometimes confused with the term environmentalism. Environmentalism is a social movement aimed at the goal of protecting natural resources or the environment, and which may involve political lobbying, activism, education, and so forth. Ecology is the science that studies living organisms and their interactions with the environment. As such, ecology involves scientific methodology and does not dictate what is «right» or «wrong.» However, findings in ecology may be used to support or counter various goals, assertions, or actions of environmentalists.

Consider the ways an ecologist might approach studying the life of honeybees:

• The behavioral relationship between individuals of a species is behavioral ecology—for example, the study of the queen bee, and how she relates to the worker bees and the drones.
• The organized activity of a species is community ecology; for example, the activity of bees assures the pollination of flowering plants. Bee hives additionally produce honey, which is consumed by still other species, such as bears.
• The relationship between the environment and a species is environmental ecology—for example, the consequences of environmental change on bee activity. Bees may die out due to environmental changes. The environment simultaneously affects and is a consequence of this activity and is thus intertwined with the survival of the species.

Disciplines of ecology

Ecology is a broad science which can be subdivided into major and minor sub-disciplines. The major sub-disciplines include:

• Physiological ecology (or ecophysiology), which studies the influence of the biotic and abiotic environment on the physiology of the individual, and the adaptation of the individual to its environment;
• Behavioral ecology, which studies the ecological and evolutionary basis for animal behavior, and the roles of behavior in enabling animals to adapt to their ecological niches;
• Population ecology (or autecology), which deals with the dynamics of populations within species and the interactions of these populations with environmental factors;
• Community ecology (or synecology) which studies the interactions between species within an ecological community;
• Ecosystem ecology, which studies the flows of energy and matter through ecosystems;
• Medical ecology, which studies issues of human health in which environmental disturbances play a role
• Landscape ecology, which studies the interactions between discrete elements of a landscape and spatial patterns, including the role of disturbance and human impacts;
• Global ecology, which looks at ecological questions at the global level, often asking macroecological questions;
• Evolutionary ecology, which either can be considered the evolutionary histories of species and the interactions between them, or approaches the study of evolution by including elements of species interaction;
• And ecolinguistics, which looks at the relation between ecology and language.

Ecology can also be sub-divided on the basis of target groups:

• Animal ecology, plant ecology, insect ecology, human ecology, and so forth.

Ecology can, in addition, be sub-divided from the perspective of the studied biomes:

• Arctic ecology (or polar ecology), tropical ecology, desert ecology, aquatic ecology, terrestrial ecology, wetland ecology, and temperate zone ecology.

Ecology can also be sub-divided on whether or not the emphasis is on application to human activities, such as resource management, environmental conservation, and restoration:

• Theoretical ecology and applied ecology (including such subfields as landscape ecology, conservation biology, and restoration ecology).

Basic concepts in ecology

Ecology is a very broad-ranging and complex topic, and even its definition lacks consensus. Thus, there are numerous concepts that fit within this discipline, and diverse manners in which the content can be arranged and studied. Several of the basic concepts of ecology include ecological units, the ecosystem, energy flow, nutrient cycles, species interaction, productivity, and ecological challenges.

Ecological units

For modern ecologists, ecology can be studied at several levels: population level (individuals of the same species), biocenosis level (or community of species), ecosystem level, biome level, and biosphere level.

The outer layer of the planet Earth can be divided into several compartments: the hydrosphere (or sphere of water), the lithosphere (or sphere of soils and rocks), and the atmosphere (or sphere of the air). The biosphere (or sphere of life), sometimes described as «the fourth envelope,» is all living matter on the planet or that portion of the planet occupied by life. It reaches well into the other three spheres, although there are no permanent inhabitants of the atmosphere. Most life exists on or within a few meters of the Earth’s surface. Relative to the volume of the Earth, the biosphere is only the very thin surface layer that extends from 11,000 meters below sea level to 15,000 meters above.

It is thought that life first developed in the hydrosphere, at shallow depths, in the photic zone (the area of water exposed to sufficient sunlight for photosynthesis). Multicellular organisms then appeared and colonized benthic zones. Terrestrial life developed later, after the ozone layer protecting living beings from UV rays formed. Diversification of terrestrial species is thought to be increased by the continents drifting apart, or alternately, colliding. Biodiversity is expressed at the ecological level (ecosystem), population level (intraspecific diversity), species level (specific diversity), and genetic level. Recently, technology has allowed the discovery of the deep ocean vent communities. This remarkable ecological system is not dependent on sunlight but bacteria, utilizing the chemistry of the hot volcanic vents, as the base of its food chain.

The biosphere contains great quantities of elements such as carbon, nitrogen, and oxygen. Other elements, such as phosphorus, calcium, and potassium, are also essential to life, yet are present in smaller amounts. At the ecosystem and biosphere levels, there is a continual recycling of all these elements, which alternate between their mineral and organic states.

A biome is a homogeneous ecological formation that exists over a vast region, such as tundra or steppes. The biosphere comprises all of the Earth’s biomes—the entirety of places where life is possible—from the highest mountains to the depths of the oceans.

Biomes correspond rather well to subdivisions distributed along the latitudes, from the equator towards the poles, with differences based on the physical environment (for example, oceans or mountain ranges) and on the climate. Their variation is generally related to the distribution of species according to their ability to tolerate temperature and/or dryness. For example, one may find photosynthetic algae only in the photic part of the ocean (where light penetrates), while conifers are mostly found in mountains.

Though this is a simplification of a more complicated scheme, latitude and altitude approximate a good representation of the distribution of biodiversity within the biosphere. Very generally, biodiversity is greater near the equator (as in Brazil) and decreases as one approaches the poles.

The biosphere may also be divided into ecozones, which are biogeographical and ecological land classifications, such as Neartic, Neotropic, and Oceanic. Biozones are very well defined today and primarily follow the continental borders.

Ecological factors that can affect dynamic change in a population or species in a given ecology or environment are usually divided into two groups: biotic and abiotic.

Biotic factors relate to living organisms and their interactions. A biotic community is an assemblage of plant, animal, and other living organisms.

Abiotic factors are geological, geographical, hydrological, and climatological parameters. A biotope is an environmentally uniform region characterized by a particular set of abiotic ecological factors. Specific abiotic factors include:

• Water, which is at the same time an essential element to life and a milieu;
• Air, which provides oxygen, nitrogen, and carbon dioxide to living species and allows the dissemination of pollen and spores;
• Soil, at the same time a source of nutriment and physical support (soil pH, salinity, nitrogen, and phosphorus content, ability to retain water and density are all influential);
• Temperature, which should not exceed certain extremes, even if tolerance to heat is significant for some species;
• Light, which provides energy to the ecosystem through photosynthesis; and
• Natural disasters can also be considered abiotic.

The ecosystem concept

Main article: Ecosystem

Some consider the ecosystem (abbreviation for «ecological system») to be the basic unit in ecology. An ecosystem is an ecological unit consisting of a biotic community together with its environment. Examples include a swamp, a meadow, and a river. It is generally considered smaller than a biome («major life zone»), which is a large, geographic region of the earth’s surface with distinctive plant and animal communities. A biome is often viewed as a grouping of many ecosystems sharing similar features, but is sometimes defined as an extensive ecosystem spread over a wide geographic area.

The first principle of ecology is that each living organism has an ongoing and continual relationship with every other element that makes up its environment. The ecosystem is composed of two entities, the entirety of life (the community, or biocoenosis) and the medium that life exists in (the biotope). Within the ecosystem, species are connected and dependent upon one another in the food chain, and exchange energy and matter between themselves and with their environment.

The concept of an ecosystem can apply to units of variable size, such as a pond, a field, or a piece of deadwood. A unit of smaller size is called a microecosystem. For example, an ecosystem can be a stone and all the life under it. A mesoecosystem could be a forest, and a macroecosystem a whole ecoregion, with its watershed.

Some of the main questions when studying an ecosystem include:

• How could the colonization of a barren area be carried out?
• What are the ecosystem’s dynamics and changes?
• How does an ecosystem interact at local, regional, and global scale?
• Is the current state stable?
• What is the value of an ecosystem? How does the interaction of ecological systems provide benefit to humans, especially in the provision of healthy water?

Ecosystems are not isolated from each other, but are interrelated. For example, water may circulate between ecosystems by the means of a river or ocean current. Water itself, as a liquid medium, even defines ecosystems. Some species, such as salmon or freshwater eels move between marine systems and fresh-water systems. These relationships between the ecosystems lead to the concept of a biome.

Energy flow

One focus of ecologists is to study the flow of energy, a major process linking the abiotic and biotic constituents of ecosystems.

While there is a slight input of geothermal energy, the bulk of the functioning of the ecosystem is based on the input of solar energy. Plants and photosynthetic microorganisms convert light into chemical energy by the process of photosynthesis, which creates glucose (a simple sugar) and releases free oxygen. Glucose thus becomes the secondary energy source that drives the ecosystem. Some of this glucose is used directly by other organisms for energy. Other sugar molecules can be converted to other molecules such as amino acids. Plants use some of this sugar, concentrated in nectar, to entice pollinators to aid them in reproduction.

Cellular respiration is the process by which organisms (like mammals) break the glucose back down into its constituents, water and carbon dioxide, thus regaining the stored energy the sun originally gave to the plants. The proportion of photosynthetic activity of plants and other photosynthesizers to the respiration of other organisms determines the specific composition of the Earth’s atmosphere, particularly its oxygen level. Global air currents mix the atmosphere and maintain nearly the same balance of elements in areas of intense biological activity and areas of slight biological activity.

See ecosystem for a more extensive explanation of energy flow in ecosystems.

Nutrient cycles

Ecologists also study the flow of nutrients in ecosystems. Whereas energy is not cycled, nutrients are cycled. Living organisms are composed mainly of carbon, oxygen, hydrogen, and nitrogen, and these four elements are cycled through the biotic communities and the geological world. These permanent recyclings of the elements are called biogeochemical cycles. Three fundamental biogeochemical cycles are the nitrogen cycle, the water cycle, and the carbon-oxygen cycle. Another key cycle is the phosphorus cycle.

Water is also exchanged between the hydrosphere, lithosphere, atmosphere, and biosphere.
The oceans are large tanks that store water; they ensure thermal and climatic stability, as well as the transport of chemical elements thanks to large oceanic currents.

Species interactions

Biocenose, or community, is a group of populations of plants, animals, and microorganisms. Each population is the result of procreations between individuals of same species and cohabitation in a given place and for a given time. When a population consists of an insufficient number of individuals, that population is threatened with extinction; the extinction of a species can approach when all biocenoses composed of individuals of the species are in decline. In small populations, consanguinity (inbreeding) can result in reduced genetic diversity that can further weaken the biocenose.

Biotic ecological factors influence biocenose viability; these factors are considered as either intraspecific or interspecific relations.

Intraspecific relations are those which are established between individuals of the same species, forming a population. They are relations of cooperation or competition, with division of the territory, and sometimes organization in hierarchical societies.

Interspecific relations—interactions between different species—are numerous, and are usually described according to their beneficial, detrimental, or neutral effect (for example, mutualism or competition). Symbiosis refers to an interaction between two organisms living together in more or less intimate association. A significant relation is predation (to eat or to be eaten), which leads to the essential concepts in ecology of food chains (for example, the grass is consumed by the herbivore, itself consumed by a carnivore, itself consumed by a carnivore of larger size). A high predator-to-prey ratio can have a negative influence on both the predator and prey biocenoses in that low availability of food and high death rate prior to sexual maturity can decrease (or prevent the increase of) populations of each, respectively. Other interspecific relations include parasitism, infectious disease, and competition for limiting resources, which can occur when two species share the same ecological niche.

In an ecosystem, the connections between species are generally related to food and their role in the food chain. There are three categories of organisms:

• Producers—plants which are capable of photosynthesis
• Consumers—animals, which can be primary consumers (herbivorous), or secondary or tertiary consumers (carnivorous).
• Decomposers—bacteria, mushrooms, which degrade organic matter of all categories, and restore minerals to the environment.

These relations form sequences in which each individual consumes the preceding one and is consumed by the one following, in what are called food chains or food networks.

The existing interactions between the various living beings go along with a permanent mixing of mineral and organic substances, absorbed by organisms for their growth, their maintenance, and their reproduction, to be finally rejected as waste. The interactions and biogeochemical cycles create a durable stability of the biosphere (at least when unchecked human influence and extreme weather or geological phenomena are left aside). This self-regulation, supported by negative feedback controls, supports the perenniality of the ecosystems. It is shown by the very stable concentrations of most elements of each compartment. This is referred to as homeostasis.

The ecosystem also tends to evolve to a state of ideal balance, reached after a succession of events, the climax (for example, a pond can become a peat bog).

Overall, the interactions of organisms convey a sense of unity and harmony (see Biology:Interactions). Plants, through photosynthesis, use carbon dioxide and provide oxygen, while animals use oxygen and give off carbon dioxide. On the level of the food web, plants capture the sun’s energy and serve as food for herbivores, which serve as food for carnivores, and ultimately top carnivores. Decomposers (bacteria, fungi, etc.) break down organisms after they die into minerals that can be used by plants.

The harmony of species’ interactions with other species and the environment, including the biogeochemical cycles, have proposed a theory by some that the entire planet acts as if one, giant, functioning organism (the Gaia theory). Lynn Margulis and Dorion Sagan in their book Microcosmos (1997) even propose that evolution is tied to cooperation and mutual dependence among organisms: «Life did not take over the globe by combat, but by networking.»

The observed harmony can be attributed to the concept of dual purpose: the view that every entity in the universe in its interactions simultaneously exhibits purposes for the whole and for the individual—and that these purposes are interdependent. «Individual purpose» refers to the individual’s requirement to met basic needs of self-preservation, self-strengthening, multiplication, and development. The «whole purpose» is that by which the individual contributes to the preservation, strengthening, and development of the larger entity of which it is a part. Thus, the cell of a multicellular body provides a useful function for the body of which it is part. This «whole purpose,» which could be the secretion of an enzyme, harmonizes with the body’s requirement of self-preservation, development, self-strengthening, and reproduction. The body, on the other hand, supports the cell’s «individual purpose» by providing essential nutrients and carrying away wastes, assisting the cell’s self-preservation, self-strengthening, multiplication, and development. Likewise, each individual organism exhibits both an individual purpose and a purpose for the whole related to its place in the environment. The result is an extraordinary harmony evident in creation.

Ecosystem productivity

The concepts dealing with the movement of energy through an ecosystem (via producers, consumers, and decomposers) lead to the idea of biomass (the total living matter in a given place), of primary productivity (the increase in the mass of plants during a given time), and of secondary productivity (the living matter produced by consumers and the decomposers in a given time).

These two last ideas are key, since they make it possible to evaluate the load capacity—the number of organisms which can be supported by a given ecosystem. In any food network, the energy contained in the level of the producers is not completely transferred to the consumers. Thus, from an energy point of view, it is more efficient for humans to be primary consumers (to get nourishment from grains and vegetables) than as secondary consumers (from herbivores such as beef and veal), and more still than as tertiary consumers (from eating carnivores).

The productivity of ecosystems is sometimes estimated by comparing three types of land-based ecosystems and the total of aquatic ecosystems:

• The forests (one-third of the Earth’s land area) contain dense biomasses and are very productive. The total production of the world’s forests corresponds to half of the primary production.
• Savannas, meadows, and marshes (one-third of the Earth’s land area) contain less dense biomasses, but are productive. These ecosystems represent the major part of what humans depend on for food.
• Extreme ecosystems in the areas with more extreme climates—deserts and semi-deserts, tundra, alpine meadows, and steppes—(one-third of the Earth’s land area) have very sparse biomasses and low productivity
• Finally, the marine and fresh water ecosystems (three-fourths of Earth’s surface) contain very sparse biomasses (apart from the coastal zones).

Humanity’s actions over the last few centuries have reduced the amount of the Earth covered by forests (deforestation), and have increased agro-ecosystems (agriculture). In recent decades, an increase in the areas occupied by extreme ecosystems has occurred (desertification).

Ecological challenges

Generally, an ecological crisis is what occurs when the environment of a species or a population evolves in a way unfavorable to that species’ survival.

It may be that environment quality degrades compared to the species needs, after a change in an abiotic ecological factor (for example, an increase of temperature, less significant rainfalls). It may be that the environment becomes unfavorable for the survival of a species (or a population) due to an increased pressure of predation (e.g., overfishing). It may be that the situation becomes unfavorable to the quality of life of the species (or the population) due to a rise in the number of individuals (overpopulation).

Although ecological crises are generally considered to be something that occurs in a short time span (days, weeks, or years), by definition, ecological crises can also be considered to occur over a very long time period, such as millions of years. They can also be of natural or anthropic origin. They may relate to one unique species or to many species (see the article on extinction).

Lastly, an ecological crisis may be local (an oil spill, a fire, or eutrophication of a lake), widespread (the movement of glaciers during an ice age), or global (a rise in the sea level).

According to its degree of endemism, a local crisis will have more or less significant consequences, from the death of many individuals to the total extinction of a species. Whatever its origin, disappearance of one or several species often will involve a rupture in the food chain, further impacting the survival of other species. Of course, what is an ecological crisis to one species, or one group of species, may be beneficial or neutral with respect to other species, at least short-term.

In the case of a global crisis, the consequences can be much more significant; some extinction events showed the disappearance of more than 90 percent of existing species at that time. However, it should be noted that the disappearance of certain species, such as the dinosaurs, by freeing an ecological niche, allowed the development and the diversification of the mammals. An ecological crisis may benefit other species, genera, families, orders, or phyla of organisms.

Sometimes, an ecological crisis can be a specific and reversible phenomenon at the ecosystem scale. But more generally, the crisis’ impact will last. Indeed, it rather is a connected series of events that occur until a final point. From this stage, no return to the previous stable state is possible, and a new stable state will be set up gradually.

Lastly, if an ecological crisis can cause extinction, it can also more simply reduce the quality of life of the remaining individuals. Thus, even if the diversity of the human population is sometimes considered threatened (see in particular indigenous people), few people envision human disappearance at short span. However, epidemic diseases, famines, impact on health of reduction of air quality, food crises, reduction of living space, accumulation of toxic or non-degradable wastes, threats on key species (great apes, pandas, whales) are also factors influencing the well-being of people.

During the past decades, this increasing responsibility of humanity in some ecological crises has been clearly observed. Due to the increases in technology and a rapidly increasing population, humans have more influence on their own environment than any other ecosystem engineer.

Some usually quoted examples as ecological crises are:

• Permian-Triassic extinction event—250 million of years ago
• Cretaceous-Tertiary extinction event—65 million years ago
• Ozone layer hole issue
• Deforestation and desertification, with the disappearance of many species
• The nuclear meltdown at Chernobyl in 1986 that caused the death of many people and animals from cancer, and caused mutations in a large number of animals and people. The area around the plant is now abandoned because of the large amount of radiation generated by the meltdown.

History of ecology

Ecology is generally spoken of as a new science, having only become prominent in the second half of the twentieth century. Nonetheless, ecological thinking at some level has been around for a long time, and the principles of ecology have developed gradually, closely intertwined with the development of other biological disciplines. There is no consensus on its beginnings, as it developed more like a multi-stemmed bush than a tree with a single trunk (Smith 1996).

Thus, one of the first ecologists may have been Aristotle or perhaps his friend and associate, Theophrastus, both of whom had interest in many species of animals. Theophrastus described interrelationships between animals and between animals and their environment as early as the fourth century B.C.E. (Ramalay 1940).

In general, the modern movement to ecology through botanical geography (which led to plant ecology) developed earlier than animal ecology. Throughout the eighteenth and the beginning of the nineteenth century, the great maritime powers such as Britain, Spain, and Portugal launched many world exploratory expeditions. These expeditions were joined by many scientists, including botanists, such as the German explorer Alexander von Humboldt. Humboldt is often considered a father of ecology. He was the first to take on the study of the relationship between organisms and their environment. He exposed the existing relationships between observed plant species and climate, and described vegetation zones using latitude and altitude, a discipline now known as geobotany.

With the publication of the work of Charles Darwin on The Origin of Species, ecology passed from a repetitive, mechanical model to a biological, organic, and hence evolutionary model. Alfred Russel Wallace, contemporary and competitor to Darwin, was first to propose a «geography» of animal species. Several authors recognized at the time that species were not independent of each other, and grouped them into plant species, animal species, and later into communities of living beings or «biocoenosis.» This term, which comes from Greek, was coined in 1877 by marine biologist Karl Möbius, and essentially means «life having something in common.»

By the nineteenth century, ecology blossomed due to new discoveries in chemistry by Lavoisier and Horace-Bénédict de Saussure, notably the nitrogen cycle. After observing the fact that life developed only within strict limits of each compartment that makes up the atmosphere, hydrosphere, and lithosphere, the Austrian geologist Eduard Suess proposed the term biosphere in 1875. He used the name biosphere for the conditions promoting life, such as those found on Earth, which include flora, fauna, minerals, matter cycles, and so forth.

In the 1920s, Vladimir Vernadsky, a Russian geologist who had defected to France, detailed the idea of the biosphere in his work The biosphere (1926), and described the fundamental principles of the biogeochemical cycles.

Ecological damages were reported in the eighteenth century, as the multiplication of colonies impacted deforestation. Since the nineteenth century, with the Industrial Revolution, more and more pressing concerns have grown about the impact of human activity on the environment. The term ecologist has been in use since the end of the nineteenth century.

Over the nineteenth century, botanical geography and zoogeography combined to form the basis of biogeography. This science, which deals with habitats of species, seeks to explain the reasons for the presence of certain species in a given location.

Pioneers in animal ecology were early twentieth-century scientists R. Hesse and Charles Eton, Charles Adams, and Victor Shelford.

It was in 1935 that Arthur Tansley, the British ecologist, coined the term ecosystem, the interactive system established between the biocoenosis (the group of living creatures), and their biotope (the environment in which they live). Ecology thus became the science of ecosystems.

Tansley’s concept of the ecosystem was adopted by the energetic and influential biology educator Eugene Odum. Along with his brother, Howard Odum, Eugene Odum wrote a textbook which (starting in 1953) educated multiple generations of biologists and ecologists in North America.

At the turn of the twentieth century, Henry Chandler Cowles was one of the founders of the emerging study of «dynamic ecology,» through his study of ecological succession at the Indiana Dunes, sand dunes at the southern end of Lake Michigan. Here Cowles found evidence of ecological succession in the vegetation and the soil with relation to age. Ecological succession is the process by which a natural community moves from a simpler level of organization to a more complex community (e.g., from bare sand, to grass growing on the sand, to grass growing on dirt produced from dead grass, to trees growing in the dirt produced by the grass).

Human ecology began in the 1920s, through the study of changes in vegetation succession in the city of Chicago, Illinois. It became a distinct field of study in the 1970s. This marked recognition that humans, who had colonized all of the Earth’s continents, were a major ecological factor. Humans greatly modify the environment through the development of the habitat (in particular urban planning), by intensive activities such as logging and fishing, and as side effects of agriculture, mining, and industry. Besides ecology and biology, this discipline involved many other natural and social sciences, such as anthropology and ethnology, economics, demography, architecture and urban planning, medicine and psychology, and many more. The development of human ecology led to the increasing role of ecological science in the design and management of cities.

The history of ecology has been one of conflicts and opposing camps. Smith (1996) notes that the first major split in ecology was between plant ecology and animal ecology, which even lead to a controversy over the term ecology, with botanists dropping the initial «o» from oecology, the spelling in use at the time, and zoologists refusing to use the term ecology at all, because of its perceived affiliation with botany. Other historical schisms were between organismal and individualist ecology, holism versus reductionism, and theoretical versus applied ecology.

References

ISBN links support NWE through referral fees

• Krebs, C.J. 1972. Ecology. The Experimental Analysis of Distribution and Abundance. New York: Harper and Row. ISBN 978-0060437701
• Margulis, L., and D. Sagan. 1997. Microcosmos: Four Billion Years of Evolution from our Microbial Ancestors. University of California Press. ISBN 978-0520210646
• Odum, E. P. 1971. Fundamentals of Ecology (3rd edition). Philadelphia: Saunders. ISBN 978-0721669410
• Ramalay, Francis. 1940. «The growth of a science.» Univ. Colorado Stud. 26: 3-14.
• Smith, R. L. 1996. Ecology and Field Biology. New York: HarperCollins College Publishers. ISBN 978-0321068811

External links

All links retrieved August 12, 2020.

• Livestock and agroecology FAO.

Content

• What is Ecology:
• Main branches of ecology
• Ecological interactions

What is Ecology:

Ecology is a branch of biology in which the interactions between living things with the habitat are studied and analyzed where they are found, that is, the relationships that exist between biotic factors (relationships between living beings) and abiotic factors (environmental conditions).

Etymologically, the word ecology derives from the Greek ökologie composed of the union of the Greek words oikos, which means ‘house’, ‘home’ or ‘dwelling’, and logos, which means ‘study’ or ‘treaty’. In this sense, ecology means ‘the study of the home’.

It was Ernst Haeckel, a German scientist, who created the term ecology in 1869 in order to designate a name for the science that studies the relationships between living things and the environment.

Therefore, the object of study of ecology It is in determining how abiotic factors (humidity, temperature, among others) interact with biotic factors (relationship between the great diversity of living beings found in the same habitat).

Hence, ecology pays particular attention to how the particular characteristics of a habitat influence the development, modification and behavior of different species.

In this sense, the concept of human ecology refers to the scientific study of the relationships between human beings and the environment, including natural conditions, interactions, and economic, psychological, social and cultural aspects. Therefore, ecology focuses on studying ecosystems or populations in general.

Likewise, ecology is a science in which carry out studies on the changes that ecosystems may undergo from the activities of human beings.

It is important to highlight the importance of ecological studies, which are multidisciplinary, which makes it possible to expand knowledge in this area of ​​science, as well as to design strategies and mechanisms focused on the preservation and conservation of the environment.

On the other hand, at present the term ecological goes beyond scientific research, it is now part of political campaigns and social movements that seek the protection and conscious interaction of the human being with the environment.

Therefore, ecology has taken on an environmentalist character and its objective is to care for and maintain the balance of human activities with those of our habitat.

See also:

• biology
• Environmental balance
• Ecosystem

Main branches of ecology

The main branches of study and research into which ecology is divided are the following:

• Autoecology: branch of ecology that studies how are the adaptations of species to certain conditions of abiotic factors.
• Demoecology (population dynamics): branch that studies, from ecology and demography, the main characteristics of the communities or population that occupy a certain habitat.
• Synecology (community ecology): branch of ecology that studies the interaction between biological communities and ecosystems.
• Agroecology: branch that starts from the knowledge of ecology and agronomy to develop food production models in which both the ecosystem and the social environment are taken into account.
• Ecophysiology (environmental ecology): branch of ecology that studies physiological phenomena in the environment, which may experience alterations due to various natural phenomena or human activity.
• Macroecology: branch of ecology that studies ecological patterns that are repeated on a large scale.

Ecological interactions

In ecology, the processes, dynamics and interactions between all living things in a population, a community, an ecosystem or the biosphere are studied.

Ecological interactions are characterized by the benefit of two living beings (harmonic) or by the detriment of one of them (inharmonious), and can occur between beings of the same species (intraspecific) or of different species (interspecific).

• Harmonic intraspecific relationships: society (organization of individuals of the same species) and colony (group of individuals of the same species with different degrees of dependence on each other).
• Inharmonious intraspecific relationships: cannibalism and intraspecific and interspecific competitions. They are equal species relationships, but there is damage on at least one side.
• Harmonic interspecific relationships: mutualism (or symbiosis), protocooperation, inquilinism (or epibiosis) and commensalism.
• Inharmonious interspecific relationships: amensalism (or antibiosis), herbivory, predation, parasitism and slavery.

Ecology is an environmental science in its most literal sense — the study of environments and the entities within it. Although closely associated with environmentalism and conservation today, it does not necessarily follow; an ecology can also be human gut flora, how the elements of an urban environment function and the ecology of soil nutrient cycles. The word “ecology” comes from the Greek and means “house study” or “living relations study”. That essentially defines what it is — the study of relationships between those who occupy a home.

Introduction to Ecology — What It Is, What it Isn’t

Ecology studies organic life, examining such elements as spatial distribution (local or general) abundance and their relationship with the environment. This includes their interaction with other organisms within that environment — essentially their “interrelatedness” as a functioning network (1, p25). It’s considered a form of environmentalism and it is usually associated with these sciences, but it also includes aspects of biology, botany, zoology, genetics, bacteriology, chemistry and physics. Ecology is about biodiversity in a given environment. It has as much in common with physiology, behavioral sciences and the evolutionary sciences as it has with environmental sciences (2) in concerning time and space.

Its main areas include:

• The processes that make up biological life including adaptation
• Distribution, abundance and spatial concentration, and biodiversity
• How and why ecosystems begin or are changed when subject to external pressures
• Changes to and movement of, energy and materials through an ecosystem. Some ecosystems can change quickly while some remain constant over longer periods

This means an ecological study can include anything from bacterial cells (3), to gut flora, through to how many generations of aphids can populate a plant, all the way up to how deserts form and maintain a constant balance, and the impact of rainforests and ice fields on the Earth’s natural processes or are impacted by planetary fluctuations (2).

A History of Ecology

Antiquity to 1900

“Ecology” is a far broader term than we perceive. As already discussed, despite being closely associated with environmental sciences, the philosophy of relationships between biological systems (the actual definition of ecology) can apply almost anywhere. The philosophy behind the various and sometimes disparate sciences emerged in the late 19^th century out of the growing interest in natural sciences — botany, zoology, and environmentalism mostly. Some argue that awareness of species and their relationships began with Aristotle, although his writings on the matter are largely lost. Aristotle’s student Theophrastus (4) described relationships between plants and animals but this was from a philosophical rather than a scientific perspective.

The first true ecological study as we would understand it is arguably the Park Grass Experiment which began in 1856 (5) and to date in 2018, is ongoing. Around 150 papers have been published on the study and it has contributed to many major areas, beginning with agriculture and evolving with time to answer new and increasingly complex questions about biodiversity and evolution, the ecological impact of humans on landscapes, and the wider changing environment. Two of Charles Darwin’s contemporaries also made their own contributions. His friend Alfred Russell Wallace looked at the geography of animal species (6). There was a growing movement within the biological sciences that recognized how species did not exist in a bubble — that they were dependent on each other.

The second contemporary was Johannes Eugenius Warming. For the first time, the scientific community started to consider the importance of environmental factors on the biological systems within it. Specifically, Warming looked at the results of fire, temperature and other abiotic influences. Warming is now considered to have created Botanical Geography (known also as biogeography and today as a division of ecology) (7) and contributed greatly to the modern discipline. It was also during the late 19^th and early 20^th century that researchers began to finally understand the massive environmental impact of 19^th-century imperialist actions such as deforestation and the concerns over upsetting the environmental imbalance of the industrial revolution.

20^th Century to The Modern Era

Ecology became a true discipline in the 20^th century following some late 19^th century developments. This was when the term “biosphere” was coined and the recognition of the strict chemical balances required for life to evolve and sustain itself was identified. Once understood, and the importance of balance realized in any biological system, ecology quickly applied to sciences other than those concerned with the environment. Vladimir I. Vernadsky, a Russian geologist who defected to France around the time of the Russian Revolution, wrote extensively about the biosphere in the aptly titled study The Biosphere published in 1926 (8). He did not coin the term. That honor goes to a fellow geologist by the name of Eduard Suess, an Austrian, in 1875. The concept of the idea of our planet and the biological systems within it making up part of a whole was born.

To some, ecology did not start truly until Arthur Tansley coined the term “ecosystem” (9). It was adopted by a number of other disciplines and taught in top academic institutions in a wide range of biological sciences. Tansley’s important work was in presenting ecology as a philosophy. This alone perhaps permitted its adoption into the theories of many scientific disciplines. Also in the early part of the 20^th century, American botanist Henry Chandler Cowles effectively founded the concept of «dynamic ecology». Studying the Indiana Dunes at the south side of Lake Michigan, he identified evidence of vegetation and soil change over large time periods (10). His work demonstrated how environmental influences change a landscape; unlike his contemporary botanists, he was largely interested in landscape change as an influencer of botanical profiles.

Tansley’s and Cowles’ work broadened the scope of ecology. Also, in the first half of the century, Charles Elton began animal ecology, but the real breakthrough was the work of British-born ecologist G. Evelyn Hutchinson and his work across New England. Under his work, ecology became an applied science as well as theoretical (11). His work impacted many subdisciplines including biogeochemistry (the impact of geological, biological and chemical actions on the environment), entomology (insects), genetics, limnology (inland water bodies), and population dynamics theory.

The Sub-Disciplines of Ecology

As already discussed, despite its strong associations with environmental studies, ecology is simply an umbrella term. There are many subdisciplines, some of which pertain to the environment, some of which do not.

Applied Ecology

This is one area where ecology applies to the environment. It’s an applied science where practitioners use ecological principles to identify and solve problems in the real world, examining challenges for the economy and human impact (12). The attempt to balance effective land use with conservation. Typical examples include agricultural management also known as agroecology, using interdisciplinary approach including genetics, animal and plant biology, conservation biology within the landscape, and environmental management. The aim of this discipline is to examine the impact of humanity on the landscape and various topographies and attempt to encourage better use so the landscape and wildlife are not damaged.

Biogeochemistry

This fuses environment with physics and the effect of biological materials on global chemistry and vice versa. It’s largely concerned with the natural physical cycles of energy and matter on our planet (11), seeking to understand chemical reactions and the balance with biological life. Through this subdiscipline of ecology, the chemical elements of nitrogen, oxygen and carbon and their interactions in all levels of the natural environment from the lithosphere (the hard outer shell of the planet) through the biosphere (the level at which life exists and can survive) to the highest level of the atmosphere and their importance for planetary ecology.

Biogeography

This area of ecology has an overlap with evolutionary biology as it concerns the study of species — particularly their geographic distribution. The distribution study of species and their related ecosystems cover geological time (so it can apply to paleontology) and geography (so it can be environmental biology and evolutionary biology). It seeks to answer questions concerning why biological species thrive in one ecological system but not in another, the effects of environmental change on species distribution on migration, contraction and spread. It’s a true multidisciplinary study, adopting elements of the environment, climate, biology, geology and evolution (13).

Chemical Ecology

This niche area examines the use of chemicals in an environment (14). This is not about pesticides or human impact, but how biological species use chemicals. It examines chemicals as defense mechanisms for example, the purposes of capsicum in chili plants as a defense, the use of sprays by skunks against predator attack, in using pheromones and other chemical substances to attract mates and mark boundaries, but also in digestive systems of animals and carnivorous plants. Biological life uses chemistry in remarkable ways; this area also looks at the impact of those chemicals on the environment.

Community Ecology

Another aspect of ecology that overlaps with biological systems and their relationships looks at how communities of species react to and interact with each other, predators and prey and other species (15). It can apply to human communities and the dynamics of social groups; it can equally apply to the rigid hierarchies of animal species such as wolves and meerkats, symbiotic relationships, co-operation between unrelated species. It is a great lens through which to view biodiversity in any ecosystem or planetary biodiversity. Biologically, it may also look at coevolution (the process by which species actions in an environment affect and influence one another) (16).

Conservation Ecology

This is the area most people think of when they hear the word “ecology” but it is only a small part of the larger umbrella term. It is, however, increasingly vital to our understanding of conservation issues, species protection and risk mitigation. Those who work in conservation ecology examine how we might change practices when working in an environment to mitigate the risk of the extinction of a species that relies on that environment to survive. They work closely with or sometimes as conservation biologists, but ecologists are more concerned with the impact of the environment, biodiversity and natural resources as a whole, rather than treating a species and its problems as existing in a bubble (17).

Ecophysiology

Also known as environmental physiology or physiological ecology, it concerns the effects of the environment on a species’ physiology. In this way, it has some overlap with evolutionary biology by looking at abiological processes, specifically environmental forcings and adaptation, rather than natural drift, and comparative physiology by attempting to explain what environmental impacts may have led to genetic drift between closely related similar species living in slightly different environments. Charles Darwin examined the finches of the Galapagos Islands which were physiologically distinct but still the same species (18). In humans, the study has been used to explain the reason for the great variation in human skin color, largely considered due to levels of sunshine.

Ecotoxicology

This small but growing area of ecology examines the ecological role of toxic materials on biological systems — on individuals, species, communities and biosphere levels. The effects of pollution on life and the environment is an ongoing problem. But rather than looking at pollution from a medical perspective, they examine broad and long-term problems for the environment — both local and large-scale level. Past studies in ecotoxicology that led to the Clean Air Act and the Environmental Protection Agency, to protect biodiversity. Rachel Carson, a marine biologist and conservationist, writer of Silent Spring in 1962, is credited with starting this area of study, separating it from the medical study of toxins (19).

Evolutionary Ecology (Also Known as Ecoevolution)

Fusing biology and evolution with ecology, this area of study considers the environmental forcings that affect species evolution. This can include a sudden change in temperature or weather variance, the presence and profile of vegetation in an area to which some of the population has migrated, the impact of predators and prey species and population pressures. It considers evolution within a community at an individual level and studies what aspects may impact the community. Each individual has a specific set of needs, creating competition which plays off against Darwin’s survival of the fittest in terms of species (20).

Fire Ecology

To many, wildfires are a natural disaster on which governments spend millions tackling and controlling. Ecologically speaking, there are vital for regenerating those ecological systems that they destroy. Fire ecologists examine the Earth’s relationship with fire in natural habitats, how they start and end, why they start in certain areas, frequency and intensity and the area’s ecological history with wildfire (21).

Functional Ecology

This area considers the pragmatic aspects of ecology — the part that certain species play in the broader ecology. Examples include predator and prey interactions, the study of the roles or functions, dependence and interdependence, that certain species (or groups thereof) play in an ecosystem to maintain balance within the system. Modern problems that they might study would include the removal of wildflowers vital to bee population, destruction of habitats vital to prey species that will, in turn, damage predator numbers (22).

Global Ecology

This is the study of the entire planet as an ecosystem and the micro and macro parts that comprise it. Our planet is a complex system where events in one area can have either local, regional or planet-wide knock-on effects. Global ecology understands the impacts that weather systems, species migration, pollution, natural events and any other localized issues can have on the other side of the planet, not a series of isolated events. It addresses the macroecological questions such as the effects of large natural disasters, global climate change and ocean acidification (23). In the 21^st century, many of its practitioners examine the human impact on the global ecology.

Human Ecology

Humans are one of the most successful species ever to have evolved on this planet. No species has changed the habitat quite in the way that we have changed it. Human ecology is an interdisciplinary approach looking at the ecological impact on the environment, biodiversity, species and adaptation of human life covering our 200,000 years of existence. It is defined as the study of humanity’s ecological dominance (deforestation for agriculture, urbanization and other changes), crossbreeding of animal and plant species and the impact that has on natural environments, and interactivity with environments — modification and adaptation.

Landscape Ecology

It is only relatively recently that we have come to understand the ecology of individual landscapes. This area of ecology examines the interactions between separate, discrete and disparate elements within a single landscape type as well as its structure, composition and functions within a wider ecology. How a landscape is defined is not always clear, but through the lens of landscape ecology, it is a system containing a specific ecological pattern. It can be a mountain range or a single hill within a wetland. It can be a freshwater floodplain and its relationship with the river or lake that runs through it (24).

Macroecology

Between landscape ecology and global ecology, this is the study of large-scale ecological phenomena that cover multiple geographic locations but are not large enough to be considered global. An example of this is continent-wide impacts of effects of a large volcanic explosion. The after effects of the Eyjafjallajökull eruption in 2010 caused severe delays to air traffic across Western Europe which had knock-on effects for American citizens wanting to cross the Atlantic to Europe and vice versa. The eruption caused disruption across a limited but important area of the northern hemisphere. The ecological problems that this caused are macroecological.

Marine Ecology and Aquatic Ecology

The interest of the ecology of water and aquatic landscapes, marine life, their relationships and interactions — both abiotic and biotic factors. Experts in this area will look at biological life at the biochemical, cellular, individual, and community. Marine ecosystems are also of interest, including the marine environment as a biosphere as well as external pressure from weather systems, and dry land ecosystems and pressure. Some examine marine geology and geography and the impact of underwater landscape on life and chemical processes (25).

Microbial Ecology

Microorganisms are vital to all life and defined as those too small to be seen by the naked eye, requiring a microscope. Specifically, microbial ecology examines the interactions, ecological needs and relationships of three lifeforms: Archaea (single cell organisms without a nucleus), Eukaryota (single or multi cell organisms with a nucleus), Bacteria and Viruses. These lifeforms exist in every ecosystem in the biosphere; no area is untouched from the deepest oceans to the highest mountains. They represent some of the oldest forms of planetary life. Understanding how they evolved and became other lifeforms could answer many questions about biological life.

Paleoecology

Landscapes change over time, sometimes through natural processes such as glacier increase or retreat. Such events in the past can have cataclysmic and fundamental changes to ecologies of all sizes, including the biological organisms that live there. It studies changes to the landscape over geological timeframes and examines extinct animals and plants (locally extinct and globally), including potential ecological reasons for that extinction, and at natural changes in the land that could have led to change in the biodiversity — immigrant and emigrant species (26).

Population Ecology

Population pressure is often just one aspect of each subdivision of ecology, but population ecology is concerned with understanding and predicting the dynamics of the spatiotemporal relationship of a single species within an ecological zone. It considers the impact that population numbers will have on an environment (27). An imbalance of predator-prey relationships where population numbers are unsustainable due to too little prey (the predators will go elsewhere, possibly permanently) or too few predators (the population of the prey species becomes uncontrollable and eats more plant life than is sustainable). Both are damaging to the environment. This can also apply to human populations, examining the impact of numbers of an ecologically-sensitive environment.

Quantitative Ecology

Mathematics as an ecological tool has already been discussed in population ecology (above) but statistics and mathematical principles can also apply elsewhere in ecology. This is the area of study that concerns hard data and numbers in understanding an ecological profile. The arrival of Big Data has permitted the growth of this (still) small area. In future, it is expected to answer to spatial, demographic and distribution questions (28) as well as attempt to shed light on population problems in marginal areas, at certain times of the year or during certain weather conditions.

Restoration Ecology

This is a subdivision of ecology that examines damage to a landscape and tries to work out what steps are required to restore it. The damage could be the result of human action (such as an oil spill) or natural (volcanic eruption, earthquake, flooding). Recent studies have shown concerted efforts to restore a landscape can lead to a reduction in forestry extinction rates (29). In the arid western states of the US, ongoing efforts in this area are succeeding in combating invasive weed species (30). The subfield has been around since the 1980s though humans have attempted to restore and maintain habitats for thousands of years.

Soil Ecology

Soil is a fascinating ecosystem in itself; vital for plant life upon which the entire food chain is dependent, soils — including the biological life (bacteria, viruses, fungi, protozoa, algae) that live in soil and the abiological processes that are part of it, including the nutrient cycle, acidity, hydration and the decomposition of organic material. This is now a separate area of study due to how reliant life is on soils, nutrients and its water content.

Theoretical Ecology

Just as most areas of science have practical or applied sides, there is also a theoretical aspect too. Ecology is no different. Ecological theory is the development of universal theories to underpin all of ecology regardless of the nature of the ecosystem. Professionals working in this area define ecological theory with statistics and other mathematical models but increasingly computer modeling, data analysis and computer simulations.

Urban Ecology

Urbanism is a small part of the human time frame, but urban environments are complex ecologies requiring separate study. Today, around 50% of the human population lives in urban centers and that is only set to grow. They have already had an enormous impact on the environment and are self-contained environments with their own ecological processes and systems. Urban ecology examines the urban environment, not just in the towns and cities as living units, but the networks required to link them together. It is also the study of urban ecological systems from the organic life that exists within it — humans and other species that have made a home too such as rodents and pests, bird species and associated biodiversity (31).

The Future of Ecology

Ecology and its various subdisciplines are entering both a challenging and exciting time. Some challenges are accelerating while new technologies could help practitioners streamline processes and aid decision-making for politicians while improving public awareness.

The Challenges of Ecology

The first and biggest challenge is in conservation ecology. Increasing species extinction due to human-induced climate change is just one factor. Already, we are seeing the impact of average temperature rises on the global ecology (32). Ecological studies are taking place across the developed world to attempt to examine what sort of impacts further temperature rises might have or is having on localized, regional and global ecologies. International agreements continue to be made and acted on to reduce carbon emissions targets. We know that ocean acidification is damaging aquatic ecologies, damaging coral and affecting biological life that depends on those ecosystems. We expect ecology and ecologists to remain at the forefront of understanding these ongoing problems and offering solutions.

Biodiversity is also a major challenge. As land clearance in ecologically sensitive areas makes way for farmland or urban landscapes, this affects the species that comprise this landscape. Loss of habitat without provision for conservation can create major imbalances between predators and their prey (33), removing vital food sources for herbivorous and carnivorous species. Urban environments are increasingly looking to improve biodiversity within their own environments (34); urban centers need not necessarily be ecologically damaging. Indeed, many of them are not — although by accident rather than design. The deliberate planting of oak trees encourages caterpillars and songbirds in an urban area of Maryland that previously had few oak trees. It’s important that urban designers and architects are made aware of and continue to promote biodiversity and enhance survival opportunities for the species that are being displaced or those that have already made a home in our urban landscapes.

Ecological damage in the developing is another cause for concern. As previously poor countries improve their economies, livelihoods, lifestyles and global economic power (35), developers are cutting down natural landscapes to make way for urban centers, factories, road network and infrastructure. Balancing these economic needs against the global ecology is expected to be a major discussion point in both international trade and climate agreements.

Access to water, water security and scarcity in coping with all of the above is likely to underpin many of our ecological problems. In the last few years, we have seen drought and wildfire in California — water shortages and excess heat exacerbate the capacity for wildfires, but this is not just a problem for arid areas during the hot season. Temperate areas are seeing faster drainage of water supplies too. Encouraging humans to use less water while population grows is vital to regional and global ecology.

Emerging Technologies and Advances in Ecology

New technologies, some unrelated to ecology but undoubtedly useful to it, could see fundamental changes to how some of these subdisciplines work with their collected data and how it may be used for a professional or general audience, and for politicians wishing to balance ecological need without hindering progress or advancement. Existing challenges are still at the forefront of the community. The first and most obvious is the advent of Big Data. We’ve largely heard about the commercial uses of this but already it’s being used in scientific applications for local, regional and global ecological issues. The Long Term Ecological Research Network established in 1980, for example, makes available four decades of data sets from long-term and large-scale ecological issues. Big Data and Cloud access mean more than ever before, researchers can access, examine and present findings more thoroughly and faster than ever before (36).

Conservation ecology has also benefited from the cheap and available technology of geographic information systems (GIS) which allows geographic big data sets to be plotted into maps, used in databases, presented and manipulated to show almost any required information. Graphic data has the benefit of presenting digestible information to non-experts including politicians, business decision makers and even the average person for whom masses of mathematical data and statistical analyses is confusing. GIS and global tracking can help researchers examine environmental changes and plot movement of species and individual biological entities. Couple this with the relative cheapness and less intrusive aspect of modern remote sensing (37).

Slightly related again is the advent of “citizen science” and crowdsourced data. This is a symptom of Big Data, not a cause, and is likely to provide useful to researchers wishing to communicate with people in areas that are beyond their resources to access. This data is useful through sheer volume that would be almost impossible for even a small team to acquire and beyond their resources to do so (38).

Sources

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• http://environment-ecology.com/what-is-ecology/205-what-is-ecology.html
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Last Updated:
10 Apr 2023
— Updated example sentences

The definition of ecology is the branch of biology that studies the relationship between organisms and their environment.

Bioecology definition

Bioecology is the specific branch of ecology dealing with the relationship between living organisms and their environment.

Many bioecologists consider that all living things must be studied as a unit when trying to determine their impact on their environment, rather than pinpointing the few which may have a more obvious effect.

This is also useful when seeking to determine the resilience of plant and animal communities to environmental stressors, such as human development for example. 

In fact, human beings have a huge impact on their environment. This may also be studied in bioecology, since humans are also members of the natural ecosystems. 

Ecology definition biology

Ecology is the branch of biology that studies all the living organisms in a given environment. It also looks at their impact on each other and the environment in question. In other words, ecology is the study of the relationships that exist in an ecosystem.

These relationships may be between members of different species, the same species, or even the living organisms and their environment. 

Ecological studies may focus on animals (animal ecology), plants (plant ecology), fungi or microorganisms to better understand the ecosystem. The ecological differences differentiating each of the species belonging to an ecosystem will determine their role and survivability in the environment. 

Ecologism definition

Ecologism is defined as a new political ideology which considers that the natural, or non-human, world is worthy of moral consideration in political, social and economic systems. This ideology came into existence with the creation of the “Green Party” political group.

They consider that current industrialist policies result in shortages in resources and social inequality and suggest a more “rational” approach which stems from a greener political ideology. 

Ecology in a sentence

Cultural ecology in a sentence

• Cultural ecology is a subdiscipline of anthropology. 
• The study of the human ability to adapt to social and physical environments is called cultural ecology. 
• We can begin to observe differences in the cultural ecology of these two groups which may stem from their differing lifestyles.
• A cultural ecology is equally as important for the future of our planet than an environmental ecology.

Ecology sentence examples

• She teaches biological concepts such as botany and ecology. 
• This is a study of the behavior, ecology, and genetics of a population of African Meerkats. 
• Since they are native to the mountains, bearded falcons play a necessary role in the ecology of the Austrian alps. 

This Biology textbook is a great read for anyone interested in topics like evolution or who wants to learn more about the terminology of ecology. 

FAQ

e·col·o·gy

 (ĭ-kŏl′ə-jē)

n. pl. e·col·o·gies

1.

a. The science of the relationships between organisms and their environments.

b. The relationship between organisms and their environment.

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[German Ökologie : Greek oikos, house; see weik- in Indo-European roots + German -logie, study (from Greek -logiā, -logy).]

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ec′o·log′i·cal (ĕk′ə-lŏj′ĭ-kəl, ē′kə-), ec′o·log′ic (-ĭk) adj.

ec′o·log′i·cal·ly adv.

e·col′o·gist n.

American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

ecology

(ɪˈkɒlədʒɪ)

n

1. (Environmental Science) the study of the relationships between living organisms and their environment

2. (Environmental Science) the set of relationships of a particular organism with its environment

3. (Sociology) the study of the relationships between human groups and their physical environment

Also called (for senses 1, 2): bionomics

[C19: from German Ökologie, from Greek oikos house (hence, environment)]

eˈcologist n

Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

e•col•o•gy

(ɪˈkɒl ə dʒi)

n.

1. the branch of biology dealing with the relations and interactions between organisms and their environment.

2. the set of relationships existing between organisms and their environment.

3. Also called human ecology. the branch of sociology concerned with the spacing and interdependence of people and institutions.

4. the advocacy of protection of the air, water, and other natural resources from pollution or its effects; environmentalism.

[1870–75; earlier oecology < German Ökologie (1868) < Greek oîk(os) house + -o- -o- + German -logie -logy]

ec•o•log•i•cal (ˌɛk əˈlɒdʒ ɪ kəl, ˌi kə-) ec`o•log′ic, adj.

ec`o•log′i•cal•ly, adv.

e•col′o•gist, n.

Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.

e·col·o·gy

(ĭ-kŏl′ə-jē)

1. The scientific study of the relationships between living things and their environments.

2. A system of such relationships: the fragile ecology of the desert.

The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

ecology, oecology

1. the branch of biology that studies the relations between plants and animals and their environment. Also called bionomics, bionomy.
2. the branch of sociology that studies the environmental spacing and interdependence of people and institutions, as in rural or in urban settings. — ecologist, oecologist, n. — ecological, oecological, adj. — ecologically, oecologically, adv.

See also: Biology

---

1. the branch of biology that studies the relationship of organisms and environments. Also called bionomics, bionomy.
2. the branch of sociology that studies the environmental spacing and interdependence of people and their institutions, as in rural or urban settings. — ecologist, oecologist, n. — ecologie, oecologic, ecological, oecological, adj.

See also: Environment

---

the branch of sociology that studies the environmental spacing and interdependence of people and their institutions. — ecologist, oecologist, n. — ecologie, oecologic, ecological, oecological, adj.

See also: Society

-Ologies & -Isms. Copyright 2008 The Gale Group, Inc. All rights reserved.

ecology

1. The study of the relationships between living organisms and their environment.

2. Study of the relationships between living things and their enviroment.

Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited