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Top-Down Limitation of Herbivorous Insects in Neotropical Forest CanopiesEPA Grant Number: U915812
Title: Top-Down Limitation of Herbivorous Insects in Neotropical Forest Canopies
Investigators: Van Bael, Sunshine A.
Institution: University of Illinois at Urbana-Champaign
EPA Project Officer: Jones, Brandon
Project Amount: $84,926
RFA: STAR Graduate Fellowships (2000) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology and Ecosystems
The objective of this research project is to determine whether herbivore populations are limited by their own predators or by the palatability/availability of food resources. This has fundamental influences on the structure of communities and on the energy flow through ecosystems. Because of conflicting theoretical and empirical work, the relative importance of predator limitation (top-down) versus resource limitation (bottom-up) in terrestrial systems remains controversial. The extent to which predation limits insect herbivores is of particular interest in tropical forest systems, where productivity and biodiversity levels are high
To address this question in two neotropical forests that differ in rainfall and species richness, we excluded birds and bats from several canopy tree species. In addition, we compared the effects of vertebrate predation in the canopy versus the understory/edge of the two forests. These forests had strata with contrasting levels of light availability, rates of leaf production, and rates of leaf turnover. We have evidence of top-down limitation for four out of six tree species at the canopy level, but we observed no effects for understory/edge saplings. In the canopy, four species showed a consistent trend of higher herbivory levels on branches where vertebrates were excluded than on control branches. Moreover, a greater number of chewing insects were observed on exclosure branches, but for pioneer tree species only. The effects of increased herbivory and higher insect abundance were greatest during the wet season.