DISSERTATION RESEARCH: Ecological aspects of species distribution limits: interaction of biotic and abiotic factors

所有物种的地理分布都是有限的。了解造成这些分布限制的因素是生态学的主要目标之一。在最简单的例子中，物理障碍限制了物种的分布。然而，在大多数情况下，这种屏障并不存在，物种沿着环境梯度逐渐减少并最终消失。理论上，当导致人口增长的参数（出生和移民）低于减少人口规模的参数（死亡和移民）时，就会出现分配极限。自达尔文以来，博物学家一直在努力了解这些种群参数如何受到环境因素的影响。历史上，生物（如竞争、捕食）和非生物（如温度、湿度）因素对种群参数的影响是分开处理的。然而，理论发展表明，这是一种过度简化，而且多种因素往往相互作用，影响人口增长和分布。然而，关于生物和非生物因素如何相互作用以形成范围边界的经验支持很少。可以说，这种限制是由于使用联合现场和实验室实验分离和测试这些因素的困难。本文提出的研究利用分布在复杂梯度（即盐度，捕食和寄生）上的两种密切相关的热带鱼物种来测试生物和非生物因素如何相互作用以限制分布。特立尼达孔雀鱼（学名Poecilia reticulata）和沼泽孔雀鱼（学名Poecilia picta）生活在特立尼达和多巴哥的河流中。特立尼达孔雀鱼是淡水居民，其分布结束于咸淡水/淡水界面。相比之下，沼泽孔雀鱼在半咸淡水中很常见，并会进入淡水，在淡水中，它们的丰度逐渐减少，接近上游分布的极限。初步数据表明，盐度本身对这两个物种的影响很小。此外，特立尼达孔雀鱼对沼泽孔雀鱼具有竞争优势，但可能对捕食者和寄生虫的直接和间接影响更为敏感。具体来说，这个项目将比较这两种孔雀鱼在以下方面的差异：(1)它们在捕食者攻击下的游泳表现；2)它们倾向于避开不利的盐度条件；3)利用互反场易位实验确定竞争、捕食和寄生如何与盐度相互作用以确定分布模式。更广泛的影响：迄今为止，共有六名本科生在论文研究方面受到了共同负责人的指导，结果是：1)完成了一篇荣誉论文；2)在Front Range学生生态研讨会上发表两张海报；3)有独立研究经验。拟议中的项目将涉及四名新本科生，其中三名来自科罗拉多州立大学（CSU），一名来自特立尼达和多巴哥的西印度群岛大学（UWI）。我们之前与UWI的教职员工和学生的接触强调了对荣誉论文项目的需求，我们将通过一个副项目提供这个机会。这名特立尼达学生将被带往科罗拉多州立大学接受额外的培训，并且所有四名学生都将有机会参与实验室和实地工作。这将使他们接触到进化生态学领域的实验设计。此外，科罗拉多州立大学的学生将在Front Range学生生态研讨会、国家会议上展示他们的研究成果，并共同撰写同行评议的论文。这将为国内和国际学生提供进入研究生院的桥梁。因此，我们认为这是进行国际合作的绝好机会。这项研究的结果将发表在科学同行评审期刊上，在国际会议上发表，并作为科罗拉多州立大学的博士论文发表。

All species show a limited geographical distribution. Understanding what factors cause these distribution limits is one of the main goals of ecology. In the simplest case, physical barriers limit the distribution of species. However, in most cases such barriers do not exist, and species gradually decline and eventually disappear along environmental gradients. In theory, distributional limits should emerge when the parameters responsible for an increase in population (birth and immigration) fall below those that reduce population size (death and emigration). Since Darwin, naturalists have been working to understand how these population parameters are affected by environmental factors. Historically, the impact of biotic (e.g. competition, predation) and abiotic (e.g. temperature, humidity) factors on the population parameters have been treated separately. However, theoretical developments have shown that this is an oversimplification, and that multiple factors often interact to affect population growth and distribution. Nevertheless, empirical support for how biotic and abiotic factors interact to shape range boundaries is scarce. Arguably, this limitation is due to the difficulties of isolating and testing these factors using joint field and laboratory experiments. The research proposed here takes advantage of two closely related tropical fish species distributed across a complex gradient (i.e. salinity, predation, and parasitism) to test how biotic and abiotic factors interact to limit distributions. The Trinidadian Guppy (Poecilia reticulata) and the Swamp Guppy (Poecilia picta) inhabit rivers of Trinidad and Tobago. Trinidadian Guppies are freshwater occupants whose distribution ends at the brackish/freshwater interface. In contrast, Swamp Guppies are common in brackish water and crosses into freshwater, where their abundance gradually decreases toward their upstream distributional limit. Preliminary data suggest that salinity alone has a small effect in the two species. Furthermore, Trinidadian Guppies are competitively dominant to Swamp Guppies, but may be more sensitive to the direct and indirect effects of predators and parasites. Specifically, this project will compare how these two guppy species differ in 1) their swimming performance under predator attacks; 2) their tendency to avoid unfavorable salinity conditions; and 3) determine how competition, predation, and parasitism interact with salinity to determine distributional patterns using reciprocal field translocation experiments.Broader Impacts: Six undergraduate students to date have been supervised by the Co-PI in the context of the dissertation research, resulting in: 1) the completion of a Honor Thesis; 2) two poster presentations at the Front Range Student Ecology Symposium; and 3) independent research experience. The proposed project will involve four new undergraduates, three from Colorado State University (CSU) and one from the University of West Indies (UWI), Trinidad and Tobago. Our previous contact with faculty and students from UWI emphasized the need for projects culminating in honors theses, and we will provide this opportunity through a side project. Using supplemental funds not requested here, the Trinidadian student will be brought to CSU for additional training, and all four students will have the opportunity to be involved in lab and fieldwork. This will expose them to experimental design in the field of evolutionary ecology. Additionally, CSU students will be presenting their results at the Front Range Student Ecology Symposium, national meetings, and to co-author peer-reviewed papers. This will provide a bridge to graduate school for both national and international students. Thus we consider this an exiting opportunity for international collaboration. Results of this research will be published in scientific peer reviewed journals, presented at international meetings and published as a PhD dissertation at Colorado State University.