DISSERTATION RESEARCH: Seedling Dynamics and Forest Diversity in Amazonian Ecuador

厄瓜多尔亚苏尼国家公园的雨林是地球上种类最多的雨林之一。各种机制被假设来解释如此大量的冠层树种在当地共存的原因。这些被提议的机制中的许多都引用了苗木招募、生长和死亡的特定模式，这些模式降低了濒临死亡的树冠树被只有一个或几个优势物种取代的可能性。本研究对这些假设进行了双管齐下的评估。首先，在整个研究森林中分布的永久普查地块中，正在对苗木的自然招募、生长和死亡速度进行量化。这些地块建立于2002年，每年都会进行监测。其次，在这些普查的基础上，将选择常见和稀有物种的焦点集合用于野外实验。这些物种的种子和幼苗的空间分布和密度将被操纵，以直接检验以下假设：1)不同物种的幼苗对特定土壤类型或微生境的限制，2)种子空间有限的传播；特别是竞争优势物种，或3)防止优势竞争物种排除相对稀有物种的频率依赖或密度依赖的死亡率。这些实验将确定不同丰度的物种(即相对稀有和相对常见)是否对实验操作表现出与每一种提出的多样化机制一致的反应。与之前雨林多样性研究的地点相比，研究森林的物种更丰富。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.