In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. This term is used only to describe biotic factors.

The term is used in various ways with slight differences in meaning. Sometimes it is limited to specific places, times, or subsets of organisms. For example, "the fish community of Lake Ontario before industrialization".

Another usage difference is whether a community is defined based on evolutionary taxonomy and biogeography, or based on function and behavior regardless of genetic relationships. For example, a plant community of the first type might be called "oak-hickory forests", while one of the second type might be called "temperate deciduous forests". The first sense of the term "community" is related to broad concepts such as ecozones and floristic provinces (such as the Neotropic ecozone or the Cape floristic region), while the second sense is related to biomes (such as the Temperate coniferous forests) (Akin, pp. 168-169).

[edit] Interspecific interactions

Species interact in various ways: competition, predation, parasitism, mutualism, commensalism, etc. The organization of a biological community with respect to ecological interactions is referred to as community structure.

[edit] Competition

Species can compete with each other for finite resources. It is considered to be an important limiting factor of population size, biomass and species richness. Many types of competition have been described, but proving the existence of these interactions is a matter of debate:

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.^[1]

[edit] Predation

Predation 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). Herbivores 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.

[edit] Mutualism

Mutualism is a symbiotic interaction between species in which both benefit, and is thus a double positive (+ +) interaction. Examples include Rhizobium bacteria growing in nodules on the roots of legume plants and insects pollinating the flowers of angiosperms.

[edit] See also

• Biocoenosis
• Community ecology
• Co-evolution
• Convergent evolution
• Evolutionary radiation
• Phage ecology#Phage community ecology
• Phylogeography
• Phytocoenosis
• Scientific classification
• Vegetation

[edit] References

• Akin, Wallace E. (1991). Global Patterns: Climate, Vegetation, and Soils. University of Oklahoma Press. ISBN 0-8061-2309-5.
• Morin, Peter J. (1999). Community Ecology. Wiley-Blackwell Press. ISBN 978-0865423503.
• Ricketts, Taylor H., Eric Dinerstein, David M. Olson, Colby J. Loucks et al. (WWF) (1999). Terrestrial Ecoregions of North America: a conservation assessment. Island Press. ISBN 1-55963-722-6.

[edit] 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.