Abstract:
Studies of trophic divergence in fishes and other organisms emphasise resource availability as a driving factor, but usually in terms of alternate resources within particular resource-limited systems. In contrast, the role of overall ecosystem productivity in shaping trophic diversity among systems has received less attention. Divergence along productivity gradients may be relevant because aquatic systems span a range of productivities, humans are accelerating the natural process of eutrophication, and productivity controls community and ecosystem processes that govern the availability and costs/benefits of alternative resources. Here, we study whether populations of white perch (Morone americana) differ in traits related to trophic divergence and how such variation might be predicted by landscape patterns of lake productivity. White perch populations differed in their body dimensions, fin lengths and gill raker structures. Each of these traits showed significant and often strong (r up to 0.91) correlations with lake Secchi depth and other metrics of lake productivity, such that white perch from more eutrophic systems tended to be larger, have more gibbous bodies, longer fins, more subterminal mouths and gill rakers with greater spacing. Isotopic 15N was correlated with phenotypic divergence, and fish from eutrophic systems exhibited a trophic shift at smaller sizes. Our results suggest that productivity has surprising ability to predict trait variation at the landscape scale. The fact that a number of the study populations were established in the last century and that some lakes became eutrophic in that period, suggests fish trophic traits can respond quickly to lake conditions.
