DISSERTATION RESEARCH: Global patterns of fish functional diversity and trait convergence along species richness and environmental gradients

群落组装过程（CAP），如环境过滤、限制相似性和中性过程，解释了物种共存和群落组成。环境过滤假设环境条件允许具有某些特征的物种建立并持续存在，导致物种特征聚集。或者，限制相似性是指具有相似特征的物种会竞争性地相互排斥，从而产生一个特征过度分散的组合。性状分散模式用于确定这些依赖于尺度的、基于生态位的（即环境中的生物、化学和物理因素）过程相对于中性过程在构建组合中的重要性。由于缺乏大规模研究、方法不一致和错误、CAP随环境梯度和物种丰富度的变化等因素，阻碍了对这些过程一般模式的研究。在独立的动物地理区域内功能群的趋同进化将为影响组合结构的生态机制提供额外的证据。生态学面临的一个主要挑战是了解群落的功能结构以及CAP在不同空间尺度上如何影响生物多样性格局。本论文研究项目有三个目标：(1)在全球范围内研究关于鱼类群落功能多样性和收敛模式的知识差距；(2)利用最近提出的分析方法确定三个尺度上限制相似性和环境过滤对中性过程的相对贡献；(3)评估不同环境和物种丰富度梯度下功能多样性和群落组合过程的变化。了解基于生态位和随机过程在不同尺度上的相对作用是群落生态学的核心目标，不仅对群落的保护和管理至关重要，而且对理解不断变化的环境对整个群落的影响至关重要。为了有效地解决这些问题，鱼类组合将在五个不同物种丰富度的不同动物地理区域的40条可涉水溪流中取样。与营养生态学、生境利用和生活史相关的性状将被测量。利用新的功能性状离散度分析方法，在三个空间尺度上检验群落聚集过程的相对贡献。功能多样性指数将在河流大小和物种丰富度梯度之间进行比较。最后，利用多元统计方法分析了不同动物地理系统中功能结构和群落聚集过程的趋同模式。实地研究将涉及与来自几个国家的科学家和学生合作。

Community assembly processes (CAP), such as environmental filtering, limiting similarity, and neutral processes, explain species coexistence and community composition. Environmental filtering posits that environmental conditions allow species with certain traits to establish and persist, causing species traits to cluster. Alternatively, limiting similarity is the idea that species with similar traits will competitively exclude each other, producing an assemblage with an overdispersion of traits. Trait dispersion patterns are used to determine the importance of these scale-dependent, niche-based (i.e., biological, chemical, and physical factors in the environment) processes in structuring assemblages relative to neutral processes. The search for general patterns of these processes has been hindered by several factors including: lack of large-scale studies, inconsistent and erroneous methodologies, and changes in CAP along environmental gradients and species richness. Convergent evolution of functional groups within independent zoogeographic regions would provide additional evidence for ecological mechanisms influencing assemblage structure. A major challenge for ecology is to understand how assemblages are functionally structured and how CAP, at varying spatial scales, influence biodiversity patterns. This dissertation research project has three aims that address these issues: (1) examine knowledge gaps regarding functional diversity and convergence patterns of fish assemblages at a global scale; (2) determine relative contribution of limiting similarity and environmental filtering to neutral processes at three scales using recently proposed analytical methods; and (3) assess changes in functional diversity and community assemblage processes across environment and species richness gradients. Understanding the relative role of niche-based and stochastic processes at various scales is a central goal in community ecology and crucial for not only conservation and management of assemblages but for understanding the effect of the ever-changing environment on communities as a whole. To effectively address these aims, fish assemblages will be sampled in forty wadable streams in five different zoogeographic regions of varying species richness. Traits with well-known relationships to trophic ecology, habitat use, and life history will be measured for each assemblage. The relative contribution of community assembly processes will be tested at three spatial scales using new methods for analysis of functional trait dispersion. Functional diversity indices will be compared across gradients of stream size and species richness. Lastly, patterns of convergence of functional structure and community assembly processes in different zoogeographic systems will be analyzed using multivariate statistical methods. Field research will involve collaborations with scientists and students from several countries.