DISSERTATION RESEARCH: Seedling Dynamics and Forest Diversity in Amazonian Ecuador

厄瓜多尔亚苏尼国家公园的热带雨林是地球上最多样化的雨林之一。 人们提出了各种各样的机制来解释当地如此大量的林冠树种的共存。 这些机制中的许多都涉及幼苗补充、生长和死亡的特定模式，这些模式降低了死亡树冠树木被一个或几个优势物种取代的可能性。 本论文的研究评估这些假设使用双管齐下的方法。 首先，自然率的招聘，生长和死亡率的幼苗正在量化的永久普查地块分布在整个研究森林。 这些地块于2002年建立，每年进行监测。 第二，根据这些普查，将选择常见和稀有物种的焦点组用于实地实验。 这些物种的种子和幼苗的空间分布和密度将被操纵，以直接检验多样性维持的假设：1）不同物种的幼苗限制在特定的土壤类型或微生境，2）空间有限的种子扩散;特别是竞争优势物种，或3）频率依赖性或密度依赖性死亡率，其阻止占优势的竞争者排除相对稀有的物种。 这些实验将确定不同丰度的物种（即，相对罕见对相对常见）表现出对实验操作的响应，与每个提出的多样化机制一致。 研究森林比以前研究雨林多样性的地方物种更丰富。 因此，这项研究将检验从其他热带森林得出的结论的普遍性。 该项目的另一个好处是，它涉及厄瓜多尔和北美科学家之间的积极合作。

The rainforest of Yasuni National Park, Ecuador, is among the most diverse on earth. Various mechanisms have been hypothesized to explain the local coexistence of such a large number of canopy tree species. Many of these proposed mechanisms invoke particular patterns of seedling recruitment, growth, and mortality that reduce the likelihood that dying canopy trees will be replaced by only one or a few dominant species. This dissertation research evaluates these hypotheses using a two-pronged approach. First, natural rates of recruitment, growth, and mortality of seedlings are being quantified in permanent census plots distributed throughout the study forest. These plots, established in 2002, are monitored annually. Second, based on these censuses, focal sets of common and rare species will be selected for use in field experiments. The spatial distributions and densities of seeds and seedlings of these species will be manipulated to directly test the hypotheses that diversity is maintained by 1) the restriction of different species' seedlings to particular soil types or microhabitats, 2) spatially limited dispersal of seeds; particularly by competitively dominant species, or 3) frequency-dependent or density-dependent mortality that prevents a dominant competitor from excluding relatively rare species. These experiments will determine whether species of differing abundances (i.e., relatively rare vs. relatively common) exhibit responses to experimental manipulation consistent each proposed mechanism of diversification. The study forest is more species-rich than sites of previous studies of rainforest diversity. Thus, the research will test the generality of conclusions drawn from other tropical forests. An added benefit of the project is that it involves active collaboration between Ecuadorian and North American scientists.