Ecology
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Ecology (from
Ecology is a branch of biology, and is the study of abundance, biomass, and distribution of organisms in the context of the environment. It encompasses life processes, interactions, and adaptations; movement of materials and energy through living communities; successional development of ecosystems; cooperation, competition, and predation within and between species; and patterns of biodiversity and its effect on ecosystem processes.
Ecology has practical applications in fields such as conservation biology, wetland management, natural resource management, and human ecology.
The term 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.
Levels, scope, and scale of organization
Ecosystems vary 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]
The main subdisciplines of ecology,
Hierarchy
System behaviors must first be arrayed into different levels of the organization. Behaviors corresponding to higher levels occur at slow rates. Conversely, lower organizational levels exhibit rapid rates. For example, individual tree leaves respond rapidly to momentary changes in light intensity, CO2 concentration, and the like. The growth of the tree responds more slowly and integrates these short-term changes.
To structure the study of ecology into a conceptually manageable framework, the biological world is organized into a
Biodiversity
Biodiversity refers to the variety of life and its processes. It includes the variety of living organisms, the genetic differences among them, the communities and ecosystems in which they occur, and the ecological and evolutionary processes that keep them functioning, yet ever-changing and adapting.
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.[11][12][13] 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.[12][14][15]
Biodiversity plays an important role in
Habitat

The habitat of a species describes the environment over which it occurs and the type of community that is formed.[23] 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."[24]: 745
Niche

Definitions of niche date back to 1917.
Niche construction
Organisms are subject to environmental pressures, but they also modify their habitats. The
Biome
Biomes are larger units of organization that categorize regions of the Earth's ecosystems, mainly according to the structure and composition of vegetation.
Biosphere
The largest scale of ecological organization is the biosphere: the total sum of ecosystems on the planet.
Population ecology
Population ecology studies the dynamics of species populations and how these populations interact with the wider environment.[40] A population consists of individuals of the same species that live, interact, and migrate through the same niche and habitat.[41]
A primary law of population ecology is the Malthusian growth model[42] which states, "a population will grow (or decline) exponentially as long as the environment experienced by all individuals in the population remains constant."[42]: 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
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.[42][43]
Using these modeling techniques, Malthus' population principle of growth was later transformed into a model known as the
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.[43][44] In cases where basic models are insufficient, ecologists may adopt different kinds of statistical methods, such as the Akaike information criterion,[45] or use models that can become mathematically complex as "several competing hypotheses are simultaneously confronted with the data."[46]
Metapopulations and migration
The concept of metapopulations was defined in 1969[47] as "a population of populations which go extinct locally and recolonize".[48]: 105 Metapopulation ecology is another statistical approach that is often used in conservation research.[49] Metapopulation models simplify the landscape into patches of varying levels of quality,[50] 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.[51] 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.[52][53]
Community ecology
Community ecology examines how interactions among species and their environment affect the abundance, distribution and diversity of species within communities.
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.[54]: 250
Ecosystem ecology
These ecosystems, as we may call them, are of the most various kinds and sizes. They form one category of the multitudinous physical systems of the universe, which range from the universe as a whole down to the atom.
The underlying concept of an ecosystem can be traced back to 1864 in the published work of
Food webs

A food web is the archetypal
Trophic levels
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
Species are broadly categorized as
Trophic levels are part of the
Keystone species

A keystone species is a species that is connected to a disproportionately large number of other species in the
Complexity
Complexity is understood as a large computational effort needed to assemble numerous interacting parts. Global patterns of biological diversity are complex. This
Holism
Holism is a critical part of the theory of ecology. 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.[80] "New properties emerge because the components interact, not because the basic nature of the components is changed."[40]: 8
Relation to evolution
Ecology and evolutionary biology are sister disciplines.
Behavioural ecology
All organisms have behaviours. Even plants express complex behaviour, including memory and communication.
Adaptation is the central unifying concept in behavioural ecology.[93] 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.[94][95]
Cognitive ecology
Cognitive ecology integrates theory and observations from evolutionary ecology and cognitive science, to understand the effect of animal interaction with their habitat on their cognitive systems.[96] "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."[97][98]
Social ecology
Social-ecological behaviours are notable in the
Coevolution

Ecological interactions can be classified broadly into a
Biogeography
Biogeography is the comparative study of the geographic distribution of organisms and the corresponding evolution of their traits in space and time.
r/K selection theory
r/K selection theory
Molecular ecology
The 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
Human ecology
A dual discipline
Only within the moment of time represented by the present century has one species man acquired significant power to alter the nature of his world.
Ecology is both a biological science and a human science.
Restoration Ecology
Ecosystem management is not just about science nor is it simply an extension of traditional resource management; it offers a fundamental reframing of how humans may work with nature.
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".[119]
Relation to the environment
The environment of ecosystems includes both physical parameters and biotic attributes. It is dynamically interlinked and contains
Disturbance and resilience
A disturbance is any process that changes or removes biomass from a community, such as a fire, flood, drought, or predation.[123] Disturbances are both the cause and product of natural fluctuations within an ecological community.[124][123][125][126] Biodiversity can protect ecosystems from disturbances.[126]
Metabolism and the early atmosphere
Metabolism – the rate at which energy and material resources are taken up from the environment, transformed within an organism, and allocated to maintenance, growth and reproduction – is a fundamental physiological trait.
The Earth was formed approximately 4.5 billion years ago.[128] 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.[129]

Throughout history, the Earth's atmosphere and
Radiation: heat, temperature and light
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
Physical environments
Water
Wetland conditions such as shallow water, high plant productivity, and anaerobic substrates provide a suitable environment for important physical, biological, and chemical processes. Because of these processes, wetlands play a vital role in global nutrient and element cycles.
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
Gravity
The shape and energy of the land are significantly affected by gravitational forces. These govern many of the geophysical properties and distributions of 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.[83] 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.[135] 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).[136]
Pressure
Climatic and
Wind and turbulence

Wind speed and turbulence influence
Fire
Plants convert carbon dioxide into biomass and emit oxygen into the atmosphere. By approximately 350 million years ago (the end of the
Soils
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
Biogeochemistry and climate
Ecologists study nutrient budgets to understand how these materials are regulated, flow, and
History
Early beginnings
By ecology, we mean the whole science of the relations of the organism to the environment including, in the broad sense, all the "conditions of existence". Thus, the theory of evolution explains the housekeeping relations of organisms mechanistically as the necessary consequences of effectual causes; and so forms the monistic groundwork of ecology.
Ecology has a complex origin.[161] Ancient Greek philosophers such as Hippocrates and Aristotle recorded observations on natural history. However, they saw species as unchanging, while varieties were seen as aberrations. Modern ecology sees varieties as the real phenomena, leading to adaptation by natural selection.[40][162][163] Ecological concepts such as a balance and regulation in nature can be traced to Herodotus (died c. 425 BC), who described mutualism in his observation of "natural dentistry". Basking Nile crocodiles, he noted, opened their mouths to give sandpipers safe access to pluck leeches out, giving nutrition to the sandpiper and oral hygiene for the crocodile.[161] Aristotle and his student Theophrastus observed plant and animal migrations, biogeography, physiology, and their behavior, giving an early analogue to the concept of an ecological niche.[164][165]
Nowhere can one see more clearly illustrated what may be called the sensibility of such an organic complex, – expressed by the fact that whatever affects any species belonging to it, must speedily have its influence of some sort upon the whole assemblage. He will thus be made to see the impossibility of studying any form completely, out of relation to the other forms, – the necessity for taking a comprehensive survey of the whole as a condition to a satisfactory understanding of any part.
Ecological concepts such as food chains, population regulation, and productivity were developed in the 1700s, through the works of microscopist Antonie van Leeuwenhoek (1632–1723) and botanist Richard Bradley (1688?–1732).[40] Biogeographer Alexander von Humboldt (1769–1859) recognized ecological gradients, where species are replaced or altered in form along environmental gradients. Humboldt drew inspiration from Isaac Newton, as he developed a form of "terrestrial physics".[167][168][169] Natural historians, such as Humboldt, James Hutton, and Jean-Baptiste Lamarck laid the foundations of ecology.[170] The term "ecology" (German: Oekologie, Ökologie) was coined by Ernst Haeckel in his book Generelle Morphologie der Organismen (1866).[171] Haeckel was a zoologist, artist, writer, and later in life a professor of comparative anatomy.[160][172]
Linnaeus founded an early branch of ecology that he called the economy of nature.
Since 1900
Modern ecology first attracted substantial scientific attention toward the end of the 19th century.
In 1942,
This whole chain of poisoning, then, seems to rest on a base of minute plants which must have been the original concentrators. But what of the opposite end of the food chain—the human being who, in probable ignorance of all this sequence of events, has rigged his fishing tackle, caught a string of fish from the waters of Clear Lake, and taken them home to fry for his supper?
Ecology surged in popular and scientific interest during the 1960–1970s environmental movement.[170] 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 (C14H9Cl5), bioaccumulating in the environment. 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.[21][170][184][185]
See also
- Lists
Notes
- romanized: khōrā, lit.'χωρα', meaning "dwelling place, distributional area" —quoted from Stauffer (1957).
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External links
- / "Ecology " entry by Alkistis Elliott-Graves in the Stanford Encyclopedia of Philosophy
- The Nature Education Knowledge Project: Ecology