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

所有物种都显示出有限的地理分布。了解是什么因素导致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，物理屏障限制了物种的分布。然而，在大多数情况下，这种障碍并不存在，物种逐渐减少，并最终沿着环境梯度消失。从理论上讲，当导致人口增长的参数（出生和移民）低于导致人口规模减少的参数（死亡和移民）时，分配界限就会出现。 自达尔文以来，博物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（如竞争，捕食）和非生物（如温度，湿度）因素对人口参数的影响已被分开处理。然而，理论的发展表明，这是一种过于简单化的看法，而且多种因素往往相互作用，影响人口的增长和分布。然而，经验支持如何生物和非生物因素相互作用，以塑造范围边界是稀缺的。可以说，这种限制是由于难以隔离和测试这些因素使用联合现场和实验室实验。这里提出的研究利用了两种密切相关的热带鱼物种分布在一个复杂的梯度（即盐度，捕食和寄生），以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（Poecilia reticulata）和沼泽孔雀鱼（Poecilia picta）栖息在特立尼达和托巴哥的河流中。特立尼达孔雀鱼是淡水居住者，其分布终止于半咸水/淡水界面。相比之下，沼泽孔雀鱼在微咸水中很常见，并进入淡水，在淡水中它们的丰度逐渐向上游分布极限下降。初步数据表明，盐度本身对这两个物种的影响很小。此外，特立尼达孔雀鱼的竞争优势，沼泽孔雀鱼，但可能更敏感的直接和间接的影响的捕食者和寄生虫。具体而言，本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）它们避免不利盐度条件的倾向; 3）确定竞争、捕食和寄生如何与盐度相互作用，以使用相互场易位实验确定分布模式。到目前为止，六名本科生已经在论文研究的背景下由Co-PI监督，导致：1）完成荣誉论文; 2）在前岭学生生态研讨会上的两个海报演示;和3）独立的研究经验。拟议的项目将涉及四名新的本科生，三名来自科罗拉多州立大学，一名来自特立尼达和托巴哥的西印度群岛大学。我们以前与教师和学生从西印度大学的接触强调了项目最终在荣誉论文的需要，我们将通过一个侧面项目提供这个机会。使用这里没有要求的补充资金，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，CSU的学生将在Front Range Student Ecology Symposium，全国会议和共同作者同行评审论文中展示他们的成果。这将为国内和国际学生提供一个通往研究生院的桥梁。因此，我们认为这是一个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审期刊上，在国际会议上发表，并在科罗拉多州立大学作为博士论文发表。

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.