Document: JOH-3-43-6

Herbivore community dynamics in wet and dry tropical forests.

BARONE, J.A.* ^1,2

Smithsonian Tropical Research Institute, Balboa, Republic of Panama ¹
Mississippi State University, Mississippi State, MS 39762 USA ²

Abstract:
Along a tropical rainfall gradient, plant communities differ in phenology, species diversity, primary productivity and anti-herbivore defenses. Little is known about how these differences influence insect herbivores across communities. As a first step in partitioning how top-down and bottom-up effects on insect herbivores differ across tropical plant communities, I conducted bi-monthly censuses of insect herbivores on leaves of juvenile plants of 21 species in a dry forest and 23 species in a wet forest in central Panama. Focusing primarily on caterpillars, the most destructive group of folivores, I found that average annual caterpillar density was significantly higher in the dry forest than the wet (0.71 vs. 0.20 caterpillars/m² leaf area, respectively; P < 0.05). This difference was due to the high density of caterpillars in the dry forest during the wet season (0.99 caterpillars/m²). In the dry season, densities were similar between the wet and dry forests (0.27 vs. 0.18 caterpillars/m², P > 0.30). In general, herbivore densities built up quickly and remained high in the dry forest during the rainy season, but dropped quickly once the dry season was in full swing. Herbivore densities were relatively constant in the wet forest, though they did decline in the most severe part of the dry season. On a host plant species basis, caterpillar species diversity was also higher in the dry forest. Higher herbivore densities in the dry forest may reflect reduced plant investment in anti-herbivore defenses, lower pressure from predators and parasitoids, or both.

Keywords: tropical forests, herbivores, caterpillars, seasonality, Panama, community dynamics

This abstract is being presented at: 3:30 PM in session:
PLANT-ANIMAL INTERACTIONS