Adaptation in nature is more complex than in controlled laboratory experiments with rapidly cycling organisms. Theory predicts that the community context will alter evolutionary responses to environmental change, and interactions among agents of selection may constrain or accelerate selection and the adaptive responses to new environmental challenges. Long-Term Ecological Research (LTER) sites are excellent laboratories to study evolution in the wild. Long-term experiments, replicated at the scale of populations, provide platforms for detecting complex evolutionary responses in diverse terrestrial and aquatic species. This research can inform both fundamental questions and management decisions as we seek to understand whether and at what rate species will adapt to environmental change.
Results/Conclusions
We describe four case studies to illustrate the power of LTER experiments for understanding evolution. (1) The foundation plant, black grama grass (Bouteloua eriopoda), dominates southwestern North American grasslands. Three years of experimental drought (66% less rain, SEV-LTER) reduced black grama survival and biomass, with clear genetic differentiation between plants that died under drought and those that survived. Reduced allelic richness in populations that survived drought suggested selection bottlenecks. A recovery-from-drought phase will study ecological feedbacks from this evolutionary change. (2) Adaptation to elevated CO2 depended on the community context in a long-term manipulation of plant species richness, atmospheric CO2 concentration, and nitrogen (BioCON, CDR-LTER). Adaptation to elevated CO2 occurred only when the species richness of the plant community during the experiment matched the species richness of the historical community of the plant population, a demonstration of the importance of the ecological community in shaping evolutionary response to environmental change. (3) Plant-rhizobia interactions are classic resource mutualisms that exchange carbon for nitrogen. Theory predicts that nutrient addition will destabilize resource mutualisms, selecting for less cooperative partners. As predicted, rhizobium populations isolated from long term nitrogen-addition plots (KBS-LTER) were less beneficial to plants than those from controls. Additional work identified the genes underlying this evolutionary response and uncovered cascading effects on community structure and soil N availability. Repeat sampling at decadal intervals will monitor the genetic mechanisms of on-going rhizobia evolution. (4) Decomposition is central to biogeochemical cycling. Long-term nitrogen additions at Harvard Forest (HFR-LTER) not only altered the community composition of fungal decomposers, but also selected for reduced decomposition rates in several fungal taxa, illustrating key feedbacks between evolution and ecosystem ecology. Together, these examples suggest untapped potential for leveraging the LTER network to study evolution in the wild under environmental change.