Resource diversity promotes among-individual diet variation, but not genomic diversity, in lake stickleback

Many generalist species consist of specialized individuals that use
different resources. This within-population niche variation can stabilize
population and community dynamics. Consequently, ecologists wish to
identify environmental settings that promote such variation. Theory
predicts that environments with greater resource diversity favor
ecological diversity (via disruptive selection or plasticity).
Alternatively, niche variation might be a side-effect of neutral genomic
diversity in larger populations. We tested these alternatives in a
metapopulation of threespine stickleback. Stickleback consume benthic and
limnetic invertebrates, focusing on the former in small lakes, the latter
in large lakes. Intermediate-sized lakes support generalist stickleback
populations using an even mixture of the two prey types, due to greater
among-individual variation in diet and morphology. In contrast, genomic
diversity increases with lake size. Thus, phenotypic diversity and neutral
genetic polymorphism are decoupled: trophic diversity being greatest in
intermediate-sized lakes with high resource diversity, whereas neutral
genetic diversity is greatest in the largest lakes.