Dissertation Research: Direct and Indirect Effects of Land Crab Herbivory on Seedling Community Structure in a Tropical Rain Forest

自20世纪60年代以来，生态学家一直在争论群落是由捕食者消耗营养链上较低的成员（自上而下）控制，还是由自下而上定义食物链的基础营养物质控制。虽然以前是两极化的，但最近出现了两种方法的综合。根据这一更复杂的分析，Hunter和Price断言，进一步认识到每个营养水平内在的功能异质性是有必要的。哥斯达黎加沿海森林的初步数据表明，草食性地蟹可能从两个营养方向显著影响幼苗群落。地蟹在森林地面上形成广泛而密集的聚集，在那里它们消耗某些种类的幼苗和落叶。地蟹通过选择性食苗，从上到下直接影响了苗木群落结构。通过将凋落叶从土壤表面转移到地下洞穴，地蟹可能自下而上地间接影响幼苗的生存，因为它们改变了幼苗的化学和物理微环境。本文提出的研究将通过实验测试地蟹对幼苗群落的异质影响，为新生的自顶向下/自底向上综合做出贡献。

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.