The Effect of Immigration on the Adaptation of Microbial Communities to Warming.

Theory predicts that immigration can either enhance or impair the rate at which species and whole communities adapt to environmental change, depending on the traits of genotypes and species in the source pool relative to local conditions. These responses, in turn, will determine how well whole communities function in changing environments. We tested the effects of immigration and experimental warming on microbial communities during an 81-day field experiment. The effects of immigration depended on the warming treatment. In warmed communities, immigration was detrimental to community growth, whereas in ambient communities it was beneficial. This result is explained by colonists coming from a local species pool preadapted to ambient conditions. Loss of metabolic diversity, however, was buffered by immigration in both environments. Communities showed increasing local adaptation to temperature conditions during the experiment, and this was independent of whether they received immigration. Genotypes that comprised the communities were not locally adapted, however, indicating that community local adaptation can be independent of adaptation of component genotypes. Our results are consistent with a greater role for species interactions rather than adaptation of constituent species in determining local adaptation of whole communities and confirm that immigration can either enhance or impair community responses to environmental change depending on the environmental context.