Evolution influences communities on many timescales. In a metacommunity context, whether local adaptation promotes or deters coexistence will depend on how influential the change is on a given interspecific interaction and the level of immigration among communities.
Over long periods of time, evolution can promote coexistence through niche partitioning, competition-colonization tradeoffs or mechanisms that make species regionally similar in fitness despite local competitive asymmetries. In addition to shaping the dynamics of interspecific interactions, evolution will impact the connectedness of a community, and thus the frequency of those interactions, by molding dispersal capabilities and habitat preference.
Empirical evidence also suggests that evolution can influence community dynamics within a short, ecologically relevant timeframe. Asymmetrical gene flow from source to sink populations can prevent efficient natural selection, leading to maladaptation in the sink and creating range limits. This type of source-sink dynamics can also decrease niche breadth and inhibit a species' ability to respond to changing biotic and abiotic environmental conditions. In the same way that intermediate dispersal can promote species diversity, intermediate gene flow can promote genetic diversity by supplying new alleles without extirpating the local genetic framework. If environmental conditions in a patch change, the genetic storage effect can provide immigrant genes adapted to the new conditions that can rescue maladapted populations. Therefore, maintaining genetic diversity on a regional scale promotes overall species diversity.
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