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Community ecology review

Key terms

CommunityAll the populations of all the different species that live together in a particular area
Species richnessThe number of species present in a community
Species diversityA measure of both species richness and relative number of species
Foundation speciesSpecies that plays an essential role in creating and defining a community
Keystone speciesSpecies that has a disproportionately large effect on community structure relative to their abundance
Invasive speciesNon-native species whose introduction causes, or can cause harm in their new area
Ecological successionA series of progressive changes in the composition of an ecological community over time
Pioneer speciesThe first species to populate an area during succession
Climax communityCommunity which has reached a steady state after ecological succession

Community structure

Community structure describes the composition of a community, and includes the number of species in that community, along with their relative numbers. Different ecological communities can be pretty different in terms of the types and numbers of species they contain.
Communities with the highest species richness tend to be found in areas near the equator, and communities with the lowest species richness lie near the poles.
Global species richness as calculated for mammal species. Image credit: "Community ecology: Figure 14," by OpenStax College, Biology, CC BY 4.0. Modification of work by NASA, CIESIN, Columbia University.
Larger numbers of species and more even abundances of species lead to higher species diversity. The higher species diversity in a community is, the more stable and able to recover from disturbances that community is.
Several factors that influence community structure include climate patterns, geography, disturbances, and interactions between organisms.

Foundation, keystone, and invasive species

Some species tend to have stronger effects on community structure than others.
Foundation species usually modify the environment so that it can support the other organisms that form the community.
Keystone species generally act in more diverse ways than foundation species, and are more likely to belong to higher trophic levels.
Invasive species may outcompete native species for resources or habitat, altering community structure and potentially leading to extinctions.

Ecological succession

Succession can occur for many different reasons. In most cases, each species affects their environment in a way that allows other species to colonize. Over time, this increases the complexity of the environment, usually increasing species diversity as well.
There are two types of succession, which differ in their starting points:
  • In primary succession, newly exposed or newly formed rock is colonized by living things for the first time. Certain hardy plants and lichens with few soil requirements, called pioneer species, colonize the area first.
During primary succession on lava in Maui, Hawaii, succulent plants are pioneer species. Image from OpenStax, CC BY 4.0.
  • In secondary succession, an area that was previously occupied by living things is disturbed, then re-colonized following the disturbance.
Forest succession over time. Image modified from Wikimedia CC BY 3.0
Over a long period of time, and assuming no further disturbances, a climax community may form when a community reaches a steady, mature state.

Mistakes and misconceptions

  • Not all non-native species become invasive. Invasive species are damaging, or have the potential to be damaging, to their new environment. They displace other species by competing with them, affecting their health, or destroying the habitat.

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