PARENT SESSION
Oral Session #9: Trophic structure and community interactions. Presiding: B. Menge.
Monday, August 6, 2001. 8:00 AM to 11:45 AM. Hall of Ideas I.
Top-down limitation of herbivorous insects in neotropical forest canopies.
VAN BAEL, SUNSHINE1, BRAWN, JEFFREY2, WRIGHT, JOSEPH3, ROBINSON, SCOTT1, 1 2 3
ABSTRACT- Ecologists debate whether herbivore population growth is limited by predation pressure or by the availability of food resources. We are currently completing a study to assess whether vertebrate predators limit herbivorous insect populations and resultant herbivory in two contrasting neotropical forests. The question of top-down limitation is addressed on a broad, community-wide scale by experimentally excluding birds and bats from several canopy tree species in the understory and canopy at two sites. Results to date suggest top-down limitation may be occurring for three out of six tree species at the canopy level. These species show a consistent trend of higher herbivory levels on canopy exclosure branches than on control branches. Effects of vertebrate predation on herbivory levels are stronger in the wet season than in the dry season. In addition, a greater number of chewing insects have been observed on exclosure branches for pioneer tree species only. Sap-feeding insects and predatory insects do not show a consistent difference between exclosure and control branches. The extent to which predation limits insect herbivores is of particular interest in a tropical forest canopy, where productivity and biodiversity levels are high. We present results from one of few studies to critically examine this question in a tropical forest canopy. We discuss how temporal and geographic variation in the limitation of herbivorous insect populations has important implications for conservation and for understanding community structure.
KEY WORDS: PLANT-ANIMAL INTERACTIONS, HERBIVORY, AVIAN INSECTIVORY