9520734 Allan Since the 1960's ecologists have debated whether communities are controlled by predators consuming members lower on the trophic chain (top-down), or by foundational nutrients defining the food chain from the bottom-up. Although previously polarized, a synthesis of the two approaches has recently emerged. In line with this more sophisticated analysis, Hunter and Price asserted that further recognition of the functional heterogeneity inherent within each trophic level is warranted. Preliminary data from Costa Rica's coastal forests suggest that the herbivorous land crabs may significantly influence seedling communities from both trophic directions. Land crabs form extensive and dense aggregations on the forest floor where they consume certain species of seedlings and fallen leaves. By selectively consuming seedlings, land crabs may directly influence seedling community structure from the top-down. By relocating leaf litter from the soil surface to their subterranean burrows, land crabs may indirectly influence seedling survivorship form the bottom-up as they alter the seedlings' chemical and physical micro-environments. The investigations proposed in this dissertation research will contribute to the nascent top down/bottom up synthesis by experimentally testing the heterogeneous influence of land crabs on the seedling community.
