In ecology

Ecology

Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

, a community is an assemblage of two or more populations of different species occupying the same geographical area. The term community has a variety of uses. In its simplest form it refers to groups of organisms in a specific place and/or time, for example, "the fish community of Lake Ontario before industrialization".

Community ecologists study the interactions between species in communities on many spatial and temporal scales, including the distribution, structure, abundance, demography

Demography

Demography is the statistical study of human population. It can be a very general science that can be applied to any kind of dynamic human population, that is, one that changes over time or space...

, and interaction

Biological interaction

Biological interactions are the effects organisms in a community have on one another. In the natural world no organism exists in absolute isolation, and thus every organism must interact with the environment and other organisms...

s between coexisting population

Population

A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

s. The primary focus of community ecology is on the interactions between populations as determined by specific genotypic and phenotypic characteristics. Community ecology has its origin in Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an plant sociology. Modern community ecology examines pattern

Pattern

A pattern, from the French patron, is a type of theme of recurring events or objects, sometimes referred to as elements of a set of objects.These elements repeat in a predictable manner...

s such as variation in species richness

Species richness

Species richness is the number of different species in a given area. It is represented in equation form as S.Species richness is the fundamental unit in which to assess the homogeneity of an environment. Typically, species richness is used in conservation studies to determine the sensitivity of...

, equitability, productivity

Productivity

Productivity is a measure of the efficiency of production. Productivity is a ratio of what is produced to what is required to produce it. Usually this ratio is in the form of an average, expressing the total output divided by the total input...

 and food web

Food web

A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

 structure (see community structure

Community structure

In the study of complex networks, a network is said to have community structure if the nodes of the network can be easily grouped into sets of nodes such that each set of nodes is densely connected internally...

); it also examines processes such as predator-prey population dynamics

Population dynamics

Population dynamics is the branch of life sciences that studies short-term and long-term changes in the size and age composition of populations, and the biological and environmental processes influencing those changes...

, succession

Ecological succession

Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...

, and community assembly.

On a deeper level the meaning and value of the community concept in ecology is up for debate. Communities have traditionally been understood on a fine scale in terms of local processes constructing (or destructing) an assemblage of species, such as the way climate change is likely to affect the make-up of grass communities. Recently this local community focus has been criticised. Robert Ricklefs

Robert Ricklefs

Dr Robert E. Ricklefs is an American ornithologist and ecologist. He is the Curators' Professor of Biology at the University of Missouri, St. Louis. Born in 1943, he graduated with an AB from Stanford University in 1963 and a Ph.D. from the University of Pennsylvania in 1967...

 has argued that it's more useful to think of communities on a regional scale, drawing on evolutionary taxonomy

Taxonomy

Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

 and biogeography

Biogeography

Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...

, where some species or clades evolve and others go extinct.

Interspecific interactions

Species interact

Biological interaction

Biological interactions are the effects organisms in a community have on one another. In the natural world no organism exists in absolute isolation, and thus every organism must interact with the environment and other organisms...

 in various ways: competition

Competition

Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...

, predation

Predation

In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

, parasitism

Parasitism

Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...

, mutualism, commensalism

Commensalism

In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...

, etc. The organization of a biological community with respect to ecological interactions is referred to as community structure.

Competition

Species can compete

Competition

Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...

 with each other for finite resources. It is considered to be an important limiting factor of population size

Population size

In population genetics and population ecology, population size is the number of individual organisms in a population.The effective population size is defined as "the number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under...

, biomass

Biomass

Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 and species richness

Species richness

Species richness is the number of different species in a given area. It is represented in equation form as S.Species richness is the fundamental unit in which to assess the homogeneity of an environment. Typically, species richness is used in conservation studies to determine the sensitivity of...

. Many types of competition have been described, but proving the existence of these interactions is a matter of debate. Direct competition has been observed between individuals, populations and species, but there is little evidence that competition has been the driving force in the evolution of large groups. For example, between amphibians, reptiles and mammals.

1. Interference competition: occurs when one population attacks, or consumes the resources, of another. Examples include a lion chasing a hyena from a kill, or a plant releasing allelopathic chemicals to impede the growth of a competing species.
2. Exploitative competition: occurs via the consumption of resources. When an individual of one species consumes a resource (e.g., food, shelter, sunlight, etc.), that resource is no longer available to be consumed by a member of a second species. Exploitative competition is thought to be more common in nature, but care must be taken to distinguish it from apparent competition.
3. Apparent competition: occurs when two species share a predator. The populations of both species can be depressed by predation without direct exploitative competition.

Predation

Predation

Predation

In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

 is hunting another species for food. This is a positive-negative (+ -) interaction in that the predator species benefits while the prey species is harmed. Some predators kill their prey before eating them (e.g., a hawk killing a mouse). Other predators are parasites that feed on prey while alive (e.g., a vampire bat feeding on a cow). Herbivore

Herbivore

Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

s feed on plants (e.g., a cow grazing). Predation may affect the population size of predators and prey and the number of species coexisting in a community.

Mutualism

Mutualism is a symbiotic interaction between species in which both benefit, and is thus a double positive (+ +) interaction. Examples include Rhizobium

Rhizobium

Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium forms an endosymbiotic nitrogen fixing association with roots of legumes and Parasponia....

 bacteria growing in nodules on the roots of legume plants and insects pollinating the flowers of angiosperms.

Community structure

A major research theme among community ecology has been whether ecological communities have a (nonrandom) structure and, if so, how to characterise this structure. Forms of community structure include aggregation

Overdispersion

In statistics, overdispersion is the presence of greater variability in a data set than would be expected based on a given simple statistical model....

 and nestedness

Nestedness

Nestedness is a measure of order in an ecological system, referring to the order in which the number of species is related to area or other factors. The more a system is "nested" the more it is organized....

.

See also

• Biocoenosis
  Biocoenosis
  A biocoenosis , coined by Karl Möbius in 1877, describes the interacting organisms living together in a habitat . This term is rarely used in English, as this concept has not been popularized in Anglophone countries...
  
  
• Co-evolution
  Co-evolution
  In biology, coevolution is "the change of a biological object triggered by the change of a related object." Coevolution can occur at many biological levels: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different...
  
  
• Convergent evolution
  Convergent evolution
  Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
  
  
• Ecological effects of biodiversity
  Ecological effects of biodiversity
  The diversity of species and genes in ecological communities affects the functioning of these communities. These ecological effects of biodiversity in turn affect both climate change through enhanced greenhouse gases, aerosols and loss of land cover, and biological diversity, causing a rapid loss...
  
  
• Evolutionary radiation
  Evolutionary radiation
  An evolutionary radiation is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment,...
  
  
• Limiting similarity
  Limiting similarity
  Limiting similarity is a concept in theoretical ecology and community ecology that proposes the existence of a maximum level of niche overlap between two given species that will allow continued coexistence....
  
  
• Population ecology
  Population ecology
  Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment. It is the study of how the population sizes of species living together in groups change over time and space....
  
  
• Phage community ecology
• Phylogeography
  Phylogeography
  Phylogeography is the study of the historical processes that may be responsible for the contemporary geographic distributions of individuals. This is accomplished by considering the geographic distribution of individuals in light of the patterns associated with a gene genealogy.This term was...
  
  
• Phytocoenosis
  Phytocoenosis
  Plant community is a collection of plant species within a designated geographical unit, which forms a relatively uniform patch, distinguishable from neighbouring patches of different vegetation types. The components of each plant community are influenced by soil type, topography, climate and human...
  
  
• Plant community
• Scientific classification
• Vegetation
  Vegetation
  Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...
  
  

Further reading

• Akin, Wallace E. (1991). Global Patterns: Climate, Vegetation, and Soils. University of Oklahoma Press. ISBN 0-8061-2309-5.
• Barbour, Burke, and Pitts, 1987. Terrestrial Plant Ecology, 2nd ed. Cummings, Menlo Park, CA.
• Morin, Peter J. (1999). Community Ecology. Wiley-Blackwell Press. ISBN 978-0865423503.
• Odum, E. P. (1959) Fundamentals of ecology. W. B. Saunders Co., Philadelphia and London.
• Ricklefs, R.E. (2005) The Economy of Nature, 6th ed. WH Freeman, USA.
• Ricketts, Taylor H., Eric Dinerstein, David M. Olson, Colby J. Loucks et al. (WWF
  World Wide Fund for Nature
  The World Wide Fund for Nature is an international non-governmental organization working on issues regarding the conservation, research and restoration of the environment, formerly named the World Wildlife Fund, which remains its official name in Canada and the United States...
  
  ) (1999). Terrestrial Ecoregions of North America: a conservation assessment. Island Press. ISBN 1-55963-722-6.

External links

• Community, BioMineWiki
• Identify microbial species in a community, BioMineWiki
• Glossary, Status and Trends of the Nation's Biological Resources, USGS.
• Glossary, ENTRIX Environmental Consultants.