Ecology

Part of a series on
Biology
Index Outline Glossary History (timeline)
Key components Cell theory Ecosystem Evolution Phylogeny Properties of life Adaptation Energy processing Growth Order Regulation Reproduction Response to environment Domains and Kingdoms of life Archaea Bacteria Protists )
Branches Abiogenesis Aerobiology Agronomy Agrostology Anatomy Astrobiology Bacteriology Biochemistry Biogeography Biogeology Bioinformatics Biological engineering Biomechanics Biophysics Biosemiotics Biostatistics Biotechnology Botany Cell biology Cellular microbiology Chemical biology Chronobiology Cognitive biology Computational biology Conservation biology Cryobiology Cytogenetics Dendrology Developmental biology Ecological genetics Ecology Embryology Epidemiology Epigenetics Evolutionary biology Freshwater biology Generative biology Genetics Genomics Geobiology Gerontology Herpetology Histology Human biology Ichthyology Immunology Lipidology Mammalogy Marine biology Mathematical biology Microbiology Molecular biology Mycology Neontology Neuroscience Nutrition Ornithology Osteology Paleontology Parasitology Pathology Pharmacology Photobiology Phycology Phylogenetics Physiology Pomology Primatology Proteomics Protistology Quantum biology Relational biology Reproductive biology Sociobiology Structural biology Synthetic biology Systematics Systems biology Taxonomy Teratology Toxicology Virology Virophysics Welfare biology Xenobiology Zoology
Research Biologist (list) List of biology awards List of journals List of research methods List of unsolved problems
Applications Agricultural science Biomedical sciences Health technology Pharming
Biology portal  Category
v t e

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.

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,

To structure the study of ecology into a conceptually manageable framework, the biological world is organized into a

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

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

Definitions of niche date back to 1917.

Organisms are subject to environmental pressures, but they also modify their habitats. The

Biomes are larger units of organization that categorize regions of the Earth's ecosystems, mainly according to the structure and composition of vegetation.

The largest scale of ecological organization is the biosphere: the total sum of ecosystems on the planet.

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

${\displaystyle {\frac {\operatorname {d} N(t)}{\operatorname {d} t}}=bN(t)-dN(t)=(b-d)N(t)=rN(t),}$

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

${\displaystyle {\frac {\operatorname {d} N(t)}{\operatorname {d} t}}=rN(t)-\alpha N(t)^{2}=rN(t)\left({\frac {K-N(t)}{K}}\right),}$

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 ${\displaystyle \alpha }$ 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 (${\displaystyle \mathrm {d} N(t)/\mathrm {d} t}$) will grow to approach equilibrium, where (${\displaystyle \mathrm {d} N(t)/\mathrm {d} t=0}$), when the rates of increase and crowding are balanced, ${\displaystyle r/\alpha }$. A common, analogous model fixes the equilibrium, ${\displaystyle r/\alpha }$ 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]

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 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

A food web is the archetypal

A keystone species is a species that is connected to a disproportionately large number of other species in the

Complexity is understood as a large computational effort needed to assemble numerous interacting parts. Global patterns of biological diversity are complex. This

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

Ecology and evolutionary biology are sister disciplines.

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 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-ecological behaviours are notable in the

Ecological interactions can be classified broadly into a

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

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

Ecology is both a biological science and a human science.

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]

The environment of ecosystems includes both physical parameters and biotic attributes. It is dynamically interlinked and contains

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]

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

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

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]

Climatic and

Forest fires modify the land by leaving behind an environmental mosaic that diversifies the landscape into different seral stages and habitats of varied quality (left). Some species are adapted to forest fires, such as pine trees that open their cones only after fire exposure (right).

Plants convert carbon dioxide into biomass and emit oxygen into the atmosphere. By approximately 350 million years ago (the end of the

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

Ecologists study nutrient budgets to understand how these materials are regulated, flow, and

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]

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.

Modern ecology first attracted substantial scientific attention toward the end of the 19th century.

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]}

Lists