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

社区组装过程（CAP），如环境过滤，限制相似性和中性过程，解释物种共存和社区组成。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，导致物种特征聚类。另一种观点是，限制相似性是指具有相似性状的物种将相互竞争，产生一个性状过度分散的组合。性状分散模式用于确定这些规模依赖的、基于生态位的（即，环境中的生物、化学和物理因素）相对于中性过程在结构化组合中的过程。这些过程的一般模式的搜索一直受到阻碍的几个因素，包括：缺乏大规模的研究，不一致和错误的方法，以及在CAP沿着环境梯度和物种丰富度的变化。在独立的动物地理区域内的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生物组合的功能结构，以及CAP如何在不同的空间尺度上影响生物多样性模式。 本论文的研究目标有三：（1）在全球尺度上研究鱼类群落功能多样性和趋同模式的知识缺口;（2）利用最近提出的分析方法，确定限制相似性和环境过滤对三个尺度上中性过程的相对贡献;以及（3）评估功能多样性和群落组合过程在环境和物种丰富度梯度上的变化。了解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，而且对了解不断变化的环境对整个群落的影响也至关重要。为了有效地解决这些目标，鱼类组合将在40个涉水流在5个不同的动物地理区域的不同物种丰富度的采样。与营养生态学，栖息地利用和生活史的关系众所周知的特征将被测量为每个组合。社区组装过程的相对贡献将在三个空间尺度上使用新的方法进行测试功能性状分散的分析。功能多样性指数将在河流大小和物种丰富度的梯度上进行比较。最后，将使用多元统计方法分析不同动物地理系统中功能结构和群落组装过程的趋同模式。实地研究将涉及与来自几个国家的科学家和学生的合作。

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.