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

• Published in: The American naturalist 2008-12, Vol.172 (6), p.761-771
• Main Authors: Srivastava, D. S., Trzcinski, M. K., Richardson, B. A., Gilbert, B.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Body Size; Bromeliaceae; Caribbean Region; Datasets; Ecosystem; Food Chain; Food chains; Food webs; Fundamental and applied biological sciences. Psychology; General aspects; Geography; Habitats; Insect larvae; Insecta; Insecta - physiology; Insects; Invertebrates; Models, Biological; Old growth forests; Predation; Predators; Rain forests; Secondary forests; Symbiosis; Trophic levels; Wildlife habitats
• ISSN: 0003-0147; 1537-5323
• DOI: 10.1086/592868

Ecologists have hypothesized that the exponent of species‐area power functions (zvalue) 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 differentzvalues 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 onzvalues may appear as differences between trophic levels. We test these alternative explanations using invertebrate food webs in 280 bromeliads from three countries. Thezvalue of predators was higher than that of prey. Much of the difference inzvalues could be explained by sampling effects but not by body size effects. When damselflies occurred in the species pool, predatorzvalues 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 inzvalues. We argue that there are often simpler explanations than trophic coupling to explain differences inzvalues between trophic levels.