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Trophic Cascades in a Tropical Endophytic Community.
Letourneau, Deborah 1, Dyer, Lee1, 1
ABSTRACT- Trophic cascade models predict changes in plant or animal biomass, but have been less explicit about how these forces may alter biodiversity. In a Costa Rican wet forest, we periodically added a predatory clerid beetle to a wet forest understory shrub (family Piperaceae) caused cascading effects through four trophic levels, with up to a 5-fold reduction in the predatory beetle's prey (a predatory ant), a 3-fold increase in herbivory, and a reduction in half of the plant's leaf area. Our current study uses the same system to assess both bottom-up and top-down effects on the invertebrate community living in the stems and hollow petioles of the tropical shrub and representing three consumer levels. After 18 months of applying plant nutrients and beetle predators in high and low light environments to 20 randomly selected, naturally occurring plants in a factorial experimental design, we harvested and dissected each plant. From the 80 dissected plants, we collected and identified, at least to morphospecies, 975 individuals in 48 taxa, excluding ants. We found that predatory beetles caused a significant reduction in abundance, but an increase in diversity of the second and third trophic levels of this endophytic community. Bottom-up effects of light and nutrients were only apparent in the detrital food web, with an increase in diversity of the second trophic level when light and nutrients were balanced.
KEY WORDS: biodiversity, bottom-up effects, top-down forces, ant-plant