Posted by: oikosasa | February 18, 2013

Hiding in the litter from the beasty ants

In the new Early View paper “Non-trophic effects of litter reduce ant predation and determine caterpillar survival and distribution”, Richard Karban and co-workers have studied the importance of litter for caterpillars hiding from ants in a hetergenous landscape. Here is Richard’s lay summery of the paper:


It is well established that trophic interactions can influence the spatial distribution and abundance of organisms.  What is less well understood is how these interactions vary across space.  In this study, we conducted several observational surveys and manipulative field experiments to examine the role of predators as drivers of caterpillar abundance and distribution across a heterogeneous landscape composed of three predominant habitat types, marsh, coastal grassland, and dune.  Unexpectedly, ants were found to readily prey upon early instar caterpillars.  The intensity of predation varied across habitat types such that caterpillars in marsh habitat had a higher probability of survival than those in drier, upland habitat. Marsh habitat in our study system is characterized by think leaf litter, while less leaf litter is associated with drier habitat.  We hypothesized that habitat substrate complexity may moderate caterpillar predation by ants. This hypothesis was supported by two findings: ant recruitment to baits decreased with litter depth and litter protected caterpillars when ants were present but not when ants were experimentally excluded. Our results show that litter confers a survival advantage to caterpillars by providing habitat, a non-trophic mechanism. In contrast to trophic effects, the importance of spatiotemporal variation of non-trophic effects in mediating species interactions has been underappreciated by many ecologists.


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