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

所有物种都表现出有限的地理分布。了解是什么因素造成了这些分布限制是生态学的主要目标之一。在最简单的情况下，物理障碍限制了物种的分布。然而，在大多数情况下，这种障碍并不存在，物种会随着环境梯度逐渐减少并最终消失。从理论上讲，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，就应该出现分配限制。自达尔文以来，自然学家一直致力于了解这些种群参数是如何受到环境因素的影响的。从历史上看，生物因素(如竞争、捕食)和非生物因素(如温度、湿度)对种群参数的影响被分开处理。然而，理论发展表明，这是一种过于简单化的说法，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，这一限制是由于使用现场和实验室联合实验分离和测试这些因素的困难。这里提出的研究利用分布在复杂梯度(即盐度、捕食和寄生)上的两个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来限制分布。特立尼达和多巴哥的河流中生活着翠鸟和沼泽石首。特里尼迪亚古皮人是淡水居住者，其分布止于半咸水/淡水界面。相比之下，沼泽古比鱼在咸水中很常见，并进入淡水，在那里它们的丰度逐渐减少，接近其上游的分布极限。初步数据表明，盐度本身对这两个物种的影响很小。此外，特里尼迪亚古皮比沼泽古比具有竞争优势，但可能对捕食者和寄生虫的直接和间接影响更敏感。具体地说，这个项目将比较这两个孔雀鱼物种在以下方面的不同：1)它们在捕食者攻击下的游泳表现；2)它们避免不利盐度条件的倾向；3)竞争、捕食和寄生如何与盐度相互作用，以确定分布模式，使用相互的野外移位实验。广泛的影响：到目前为止，在论文研究的背景下，Co-PI已经指导了6名本科生，结果是：1)完成了一篇荣誉论文；2)在前端学生生态学研讨会上做了两次海报演示；以及3)独立的研究经验。拟议的项目将涉及四名新本科生，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西印度群岛大学(UWI)。我们之前与威斯康星大学的教职员工和学生的接触强调了项目最终获得荣誉论文的必要性，我们将通过一个附带项目来提供这个机会。使用这里没有申请的补充资金，这名特立尼达学生将被带到CSU进行额外的培训，所有四名学生都将有机会参与实验室和实地考察。这将使他们接触到进化生态学领域的实验设计。此外，南加州大学的学生将在前沿学生生态研讨会、全国会议上展示他们的成果，并共同撰写同行评议论文。这将为国内和国际学生提供进入研究生院的桥梁。因此，我们认为这是开展国际合作的绝佳机会。这项研究的结果将发表在科学同行评议的期刊上，在国际会议上发表，并作为博士论文在科罗拉多州立大学发表。

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.