Quantifying interactions between ecological and evolutionary processes in natural landscapes
Patterns of variation at the population genetic and community ecological level are traditionally studied in isolation of one another. However, populations and communities inhabit the same landscape and are both structured by landscape features such as environmental gradients and spatial connectivity. Additionally, evolution and adaptation to local environmental conditions in one species may actually influence species interactions, producing observed community composition patterns that differ from those expected in the absence of evolution. We will present results from a series of research projects designed to address these complex but realistic possibilities in communities of freshwater zooplankton inhabiting small ponds in Belgium.
In one study, we simultaneously evaluated patterns of variation at the population genetic and community ecological level. We combined data typically collected to understand population genetic structure and local adaptation with data typically collected to understand ecological community and metacommunity structure. We chose 20 study sites to characterize zooplankton community composition and life history trait distributions, environmental properties, and geographic connectivity to other sites. In addition to this, we genotyped individuals of the keystone herbivore, Daphnia magna, and measured a suite of its life history traits in a common garden laboratory environment. We found two critical environmental gradients - nearby land use or clear vs. turbid water regime state – that structured both populations and communities. Variables associated with these gradients explained anywhere from 10-60% of the among-site variation in community composition, community average trait values, and D. magna traits. This greatly exceeded the signal of environmental features structuring D. magna neutral markers, providing clear evidence for local adaptation in D. magnapopulations and species sorting in zooplankton metacommunities in response to the same environmental selection pressures.
In another study, we combined experimental evolution trials in D. magna to promote adaptation to particular environmental conditions with community assembly experiments to determine the effect of D. magna adaptation on zooplankton community composition. Adaptive evolution in D. magna caused substantial and repeatable changes to zooplankton communities. The magnitude of these changes (D. magna local adaptation explained 11% of the variation in composition in our mesocosm communities) was as large as ecological drivers of composition (the presence of zooplanktivorous fish and of an aquatic plant that served as habitat refuge explained 10% and 15% of variation in community composition, respectively). The mechanism of evolution's influence on competitors varied between competitive exclusion and facilitation, where D. magna adaptation actually increased the relative abundance of competitors.