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

9520734自20世纪60年代以来，S生态学家一直在争论群落是由捕食者控制的(自上而下)，还是由自下而上定义食物链的基本营养物质控制的。尽管以前两极分化，但最近出现了这两种方法的综合。根据这一更复杂的分析，亨特和普莱斯断言，有必要进一步认识到每个营养水平内在的功能异质性。来自哥斯达黎加沿海森林的初步数据表明，草食性陆蟹可能会从两个营养方向对苗木群落产生重大影响。陆地蟹在森林地面上形成广泛而密集的聚集地，在那里它们吃掉某些种类的幼苗和落叶。陆蟹通过选择性取食苗木，自上而下直接影响苗木群落结构。通过将落叶从土壤表面转移到地下洞穴，陆蟹可能会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。本文提出的研究将有助于通过实验测试陆蟹对苗木群落的异质性影响，从而为新生的自上而下/自下而上的合成做出贡献。

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.