Ecological Causes and Consequences of Trait Divergence in Invasive White Perch (Morone americana)

Evolutionary processes are now known to occur on contemporary, ecological time scales, leading both ecologists and evolutionary biologists to consider the importance of evolutionary dynamics to a variety of fields typically considered to be within the purview of ecology. However, the generality of interactions between ecology and evolution and the potential for dynamic feedbacks (i.e., eco-evolutionary dynamics) are poorly understood. In this research I addressed the hypothesis that trophic divergence in white perch (Morone americana) driven by a gradient of lake productivity would alter lake community structure and ecosystem function. The phenomenon of trophic divergence is commonly studied in sympatry; however, more modest trophic divergence may be common along environmental gradients in allopatry. Productivity is a dominant axis of ecological variation and was analyzed as a driver of perch trophic traits. Surveys across a productive state gradient of lakes revealed variation in a suite of perch traits, which suggested a benthic-eutrophic versus limnetic-oligotrophic dichotomy driven by relative resource availability in oligotrophic versus eutrophic lakes. Populations in eutrophic systems exhibited wider mouths and gill raker spacing, gibbose body shape, and longer fins compared to populations in oligotrophic systems. Trophic divergence was further associated with stroichiometric divergence, which can have ecological consequences in its own right. Modeling of stoichiometric divergence suggests it may explain between 5 and 24% of nitrogen and phosphorus excretion variation in fish populations. Considering predictions from trophic cascade and also ecological stoichiometry theory, I expected differential feeding in benthic versus limnetic habitats would lead to divergent ecological roles. Using mesocosm habitats stocked with fish from different source populations, I found that phenotype divergence in white perch altered several community and ecosystem parameters, including benthic invertebrates, nutrient concentrations and the production and limitation of primary producers. Importantly, these effects of fish phenotype varied with respect to background environmental conditions, suggesting that eco-evolutionary effects can be context dependent. In the perch system, context- dependent eco-evolutionary effects occur in a pattern which could reinforce the effects of cultural eutrophication in shifting lake systems to an alternate stable state