The fields of ecology and evolution both provide theories to explain the strong association between species’ traits and local environmental conditions. This association could result from niche-based community ecological processes such as species sorting, or from the evolutionary process of local adaptation. Since these community ecological and evolutionary theories developed independently, few guidelines tell us when to expect evolutionary adaptation or ecological species sorting as the primary driver of species and trait composition in a given habitat. The goal of our analysis was to determine how sorting among and evolution within species in a metacommunity influenced trait change after an environmental disturbance. We modeled the ecological and evolutionary dynamics of a competing metacommunity of primary producers that absorb inorganic nutrients and suffer grazing from primary consumers. Our evolving metacommunity framework considered both spatial complexity, with multiple heterogeneous sites, and ecological complexity, with multiple levels of a food chain. We analyzed how changes in two key parameters – dispersal rate of competing species and genetic variance within these species – influenced community trait change after environmental fluctuations.
Results/Conclusions
We found that both evolution and species sorting in metacommunities led to species whose traits corresponded strongly to local environmental conditions. When dispersal was low, local adaptation by the resident species accounted for most trait changes in the disturbed patch. As dispersal rate increased, species from more suitable patches colonized and excluded the resident species. As genetic variance increased, adaptation proceeded more efficiently and led to source-sink dynamics. Well-adapted populations in one patch maintained sink populations in other patches, and drove better adapted resident species extinct.
Environmental disturbance is a natural feature in many communities. However, human-related activity has increased its occurrence and severity. Many communities respond to environmental disturbances such as acidification, climate change, or eutrophication via shifts in community composition. Clear adaptive shifts in heritable phenotypic traits in response to environmental change have also occurred in other species. Because theories in the fields of evolutionary biology and community ecology developed independently, there are no expectations of when the primary driver of trait composition will be ecological species sorting or evolutionary adaptation. Our model indicates that the dispersal rate of species and their genetic variance determine the relative importance of these two processes.