Why Are Predators More Sensitive to Habitat Size than Their Prey? Insights from Bromeliad Insect Food Webs.

TitleWhy Are Predators More Sensitive to Habitat Size than Their Prey? Insights from Bromeliad Insect Food Webs.
Publication TypeJournal Article
Year of Publication2008
AuthorsSrivastava, DS, Trzcinski, MK, Richardson, B, Gilbert, J
JournalThe American Naturalist
Issue172
Pagination761-771
Accession NumberLUQ.991
Keywordsincidence functions, phytotelmata, predation, species-area relationship, trophic rank hypothesis
Abstract

Ecologists have hypothesized that the exponent of species-area power functions (z value) should increase with trophic level. The main explanation for this pattern has been that specialist predators require prior colonization of a patch by their prey, resulting in a compounding of the effects of area up trophic levels. We propose two novel explanations, neither of which assumes trophic coupling between species. First, sampling effects can result in different z values if the abundances of species differ (in mean or evenness) between trophic levels. Second, when body size increases between trophic levels, effects of body size on z values may appear as differences between trophic levels. We test these alternative explanations using invertebrate food webs in 280 bromeliads from three countries. The z value of predators was higher than that of prey. Much of the difference in z values could be explained by sampling effects but not by body size effects. When damselflies occurred in the species pool, predator z values were even higher than predicted, as damselflies avoid small, drought-prone bromeliads. In one habitat, dwarf forests, detrital biomass became decoupled from bromeliad size, which also caused large trophic differences in z values. We argue that there are often simpler explanations than trophic coupling to explain differences in z values between trophic levels.

DOI10.1086/592868
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