Metacommunities: Spatial Community Ecology

Abstract

Ecology explains the distribution and abundance of species from small to large spatial scales. Explanations based only on processes operating at local scales do not fully account for patterns of diversity at regional scales. Recent decades have seen the unification of local and regional processes as explanations for the maintenance of diversity within the metacommunity concept. A metacommunity is a set of local communities connected by dispersal of multiple potentially interacting species. Metacommunity ecology studies the interactions among species as they occur across a network of patches. The rate and frequency of dispersal mediates the spatial distribution of diversity, abundance and the flux of energy across the metacommunity. The metacommunity concept also provides a deeper understanding of the causes and consequences of species loss, and suggests solutions to mitigate these effects.

Key concepts

  • Concept: Summary

  • Colonization: A spatial process in which a population becomes established in an area where it was previously absent.

  • Open community: A community that experiences immigration and emigration.

  • Metacommunity dynamics: The dynamics of species abundances and distribution within a metacommunity due to the compound effects of species interactions and dispersal.

  • Local versus regional processes: Local processes occur within a community and include density‐dependent growth and interspecific interactions, whereas regional processes occur across communities and include dispersal.

  • Source–sink system: A network of patches of a single species connected by dispersal containing two categories of population types: (1) source populations, in which the birth rate exceeds the death rate and emigration is common and (2) sink populations, in which the death rate exceeds the birth rate and frequent immigration is required to sustain the presence of individuals.

  • Rescue effect: A spatial process in which local extinction is prevented by immigration from other patches in the metacommunity. The rate of immigration per patch increases as the proportion of patches occupied increases.

  • Neutral model: All species are assumed to be identical with respect to their birth and death rates (fitness). Stabilizing mechanisms are absent, and the abundances of all species drift randomly to extinction. Diversity is maintained in the long‐term by speciation.

  • Extinction debt: The delayed loss of species that occurs long after the initial loss of habitat connectivity.

  • Spatial insurance hypothesis: The dispersal‐dependent maintenance of biodiversity and ecosystem processes within a metacommunity.

Keywords: diversity; dispersal; species interactions; extinction; colonization

Figure 1.

Diagram showing the hierarchical structure of units used in the text to define a metacommunity (see text for definitions).

Figure 2.

The dispersal of species among patches within the community strongly modulates the levels of all three components of diversity within the metacommunity. This figure redrawn from Mouquet and Loreau shows that local diversity (α) increases to a maximum at intermediate dispersal rates, whereas between community diversity (β) and regional diversity (γ) decreases as dispersal increases. In the absence of dispersal only the competitively superior species excludes all others in each patch; at intermediate dispersal rates the inferior species are sustained by dispersal from source patches elsewhere, whereas at high dispersal the best competitor under the average conditions across the metacommunity dominates and excludes all others.

Figure 3.

The spatial insurance hypothesis connects diversity to ecosystem function in metacommunities. (a) At very low dispersal rates (thin arrows) each habitat patch maintains a single species (coloured area corresponds to the distribution of individuals of a single species) that is best adapted to the local conditions in each patch. At intermediate dispersal rates the number species per patch is maximal because of a source–sink effect. Note that each patch maintains several species but that only one species is dominant (large coloured area) whereas the others are of low abundance (small coloured area). Ecosystem variability ((b), measured by the coefficient of variation, CV) is lowest and productivity (c) is greatest at this level of dispersal (grey zone) because of the insurance effects of biodiversity (see text for explanation). At high dispersal rates only one species is present through out the metacommunity. This species is the best competitor under the average conditions across all patches, and excludes all others. Biodiversity has collapsed and ecosystem productivity is maintained only by spatial‐averaging.

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Further Reading

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How to Cite close
Gonzalez, Andrew(Dec 2009) Metacommunities: Spatial Community Ecology. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021230]