Some of the methodology used to infer the magnitude of bird predation on caterpillars in forest sites that vary in area (degree of fragmentation): bird exclosure on witch hazel (left), clay caterpillar on red maple (right) (photos by Michael S. Singer).
In collaboration with Drs. Robert Bagchi, David Wagner, and Christopher Elphick at U. Connecticut, I am extending the tri-trophic work in Connecticut forests into the realm of landscape fragmentation. This project is my current focus because we have been awarded NSF funding to work on it. As has been seen more generally with habitat specialist species, we observed that more fragmented forest harbors fewer dietary specialist caterpillars relative to dietary generalist caterpillars. Our project tests several alternative hypothetical mechanisms for this pattern. As discussed in our review paper on this topic (Bagchi et al. 2018, Oecologia), these mechanisms include neutral sampling effects on the plant community due to limited habitat area, disrupted top-down control of dietary generalist caterpillars by bird predation due to area effects and/or altered habitat quality for songbirds, and altered deer-browsing effects on the plant community. Other work has shown that intensive deer browsing can eliminate from the community plant species that host the highest caterpillar densities. It is also possible that intraspecific differences in host-plant quality for caterpillars somehow leads to greater fitness in large forest fragments versus small ones. We will consider these mechanisms to test the hypothesis that the fitness costs incurred by dietary specialist caterpillars are more severe than those incurred by dietary generalist caterpillars on woody host plants occurring in fragmented forest stands.