Evolutionary change depends on community context in BioCON, a long-term field study

Background/Question/Methods

Understanding how species adapt to environmental change is critically important, yet most experimental studies investigate adaptation on single isolated species. This is problematic as species do not live in isolation – they live in complex communities where they interact with many other species. Because ecological interactions, such as competition, can directly alter fitness components, the direction of selection, and population size, studies on isolated species may not accurately predict the response to environmental change in complex communities. We investigated how community context influences evolution in a natural ecosystem exposed to elevated carbon dioxide (CO₂). Fieldwork was carried out in a long-term ecological experiment, BioCON, at the Cedar Creek Ecosystem Science Reserve in Minnesota. BioCON was initiated in 1997 and maintains differing diversities of plants (from 1 to 16 species) under ambient or elevated CO₂ conditions. In June 2011 we collected Poa pratensis (Kentucky Bluegrass) seeds from plots that were kept as either monocultures or 16-species plots under ambient and elevated CO₂ conditions.  We then grew these seeds in a common garden environment to reduce maternal effects. From these common garden plants we collected rhizomes that we transplanted back into the BioCON plots using a full reciprocal transplant design.

Results/Conclusions

Results from our transplant experiment indicated that both plastic and genetic changes occurred in response to elevated CO₂, with the magnitude of such changes influenced by species diversity in the plot of origin. We found significant main effects of diversity (p<0.001) and CO₂ (p<0.05) in the environment into which rhizomes were transplanted on all traits measured, indicating plastic trait responses independent of the environment from which the rhizomes originated. We also found that the environment from which rhizomes originated significantly affected the number of leaves produced by each plant (CO₂: p<0.01; diversity: p<0.001), suggesting that plants have adapted via genetic change in this trait to their local conditions. In addition to these main effects we found several interactions, such as diversity origin x diversity current (p<0.05) and CO₂ origin x diversity origin x CO₂ current (p<0.05) for plant height. These interactions demonstrate that the community context in which a species has evolved has influenced the extent of adaptation to local conditions. Overall, these results indicate that the diversity of the competitive community can influence how species evolve to deal with changing abiotic conditions.