Columnar Cacti; A Critical Resource For Avian Consumers? Quantifying Avian Community Responses and Nutrient Fluxes in Natural and Experimental Settings

大型柱状仙人掌，如仙人掌（Carnegiea gigantea）是许多生态系统的突出特征。由于其广泛分布和大量多汁果实的生产，它们在构建食物网和生态系统中起着重要作用。然而，到目前为止，研究植物-果实共生关系的生态和进化方面的研究人员在很大程度上忽略了这一重要的植物群体。这些多汁的水果在炎热的沙漠中可能特别重要，因为高温和缺水可能会限制动物的行为，以及繁殖的时间和投资。在索诺兰沙漠夏季最干燥和最热的时期（6月至7月），在季风降雨开始之前，瓜罗的果实可以得到。在这项研究中，我使用了两方面的方法来评估一种独特的资源，即壁虎，对鸟类消费者群体的重要性。拟议的研究有几个特点，使其与早期研究植物-动物相互作用的研究不同：1)它结合了个体消费者使用资源的观察数据，并使用稳定同位素占星剂直接测量植物资源和消费者群体之间的营养转移；2)它量化了水果可用性的时间变化以及鸟类丰度、多样性和生产力的变化；3)它通过水果去除直接操纵资源可用性，同时量化了消费者丰度、多样性和生产力的变化。综上所述，这些研究提供了一种独特的方法来评估假定的非关键或非基础资源的重要性：1)直接量化初级生产者和个人消费者之间的营养流动；2)通过水果去除实验，检查水果资源对消费者丰度、生物多样性和生产力的影响。我希望这项研究能够产生一系列广泛的新见解：1)沙漠鸟类的水和能量平衡；2)仙人掌在干旱半干旱生态系统中的消费资源作用；3)植物与消费者之间相互作用的果实和养分转移速率；4)与资源水平变化相关的群落动态。这项工作还将量化不同的消费群体（种子捕食者和种子传播者）如何与植物相互作用，从而影响植物的繁殖潜力。它将首次对研究资源利用的传统方法与使用稳定同位素的新技术进行比较分析。与此同时，这将是第一批量化移除“楔石”植物资源对整个动物群落的丰度、多样性和繁殖产出的影响的研究之一。这项研究也将是第一个量化单一资源对任何生态系统中不同体型、觅食模式和饮食行业的多种物种的营养和水分平衡的重要性。这一工作也将为家庭范围大小和觅食方式如何影响个体对资源系统的利用提供重要的新经验证据。最后，本研究将把科学过程的各个方面带给大量的研究生和本科生。20名本科生和1名研究生将在这个项目中获得丰富的研究经验，很可能会有更多的人通过REU项目接受培训。由于我与亚利桑那-索诺拉沙漠博物馆的关系，这项研究必然也会对公众产生重大影响。该项目的研究成果将成为博物馆中心展览的基础，探索科学过程以及萨瓜罗与索诺兰沙漠其他居民的互动。

Large columnar cacti, such as the saguaro (Carnegiea gigantea), are prominent features ofmany ecosystems. Because of their extensive distribution and abundant production of largesucculent fruit they play an important role in structuring food webs and ecosystems. Up untilnow, however, researchers studying the ecological and evolutionary aspects of plant-frugivoremutualisms have largely ignored this important group of plants. These succulent fruit may beparticularly important in hot deserts where high air temperatures and water scarcity mayconstrain animal behavior as well as the timing and investment in reproduction. The saguaro'sfruit are available during the driest and hottest period (June-July) of the summer in the SonoranDesert, before the onset of monsoon rains.In this research, I use a two-faceted approach to assessing the importance of a uniqueresource, the saguaro, to a community of avian consumers. The proposed research has severalfeatures that set it apart from earlier studies examining plant -animal interactions: 1) it combinesobservational data of resource use by individual consumers with direct measurements nutrienttransfer between the plant resource and a community of consumers using stable isotopes astracers; 2) it quantifies both temporal changes in fruit availability and changes in avianabundance, diversity, and productivity and 3) it directly manipulates resource availability,through fruit removal, while quantifying changes in consumer abundance, diversity, andproductivity. Taken in concert, these studies provide a unique approach to assessing theimportance of presumed irkeystonely or irfoundationlr resources by: 1) directly quantifying theflux of nutrients between a primary producer and individual consumers and 2) through a fruitremoval experiment, examining the effects of the fruit resource on consumer abundance,biodiversity, and productivity.I expect this research to produce an extensive array of new insights into: 1) the water andenergy balance of desert birds; 2) the role of cacti as consumer resources in arid and semi-aridecosystems; 3) frugivory and nutrient transfer rates between plant-consumer interactions and 4)community dynamics as it relates to changes in resource levels. This work will also quantify howdifferent consumer groups (seed predators versus seed dispersers) interact with the plant to affectthe plant's reproductive potential. It will provide the first comparative analysis of traditionalmethods of studying resource use to the newer techniques using stable isotopes.At the same time, it will be among the first studies to quantify the effects of removal of apresumed irKeystone Plant Resourcele on the abundance, diversity and reproductive output of anentire animal community. This research will also be the first to quantify the importance of asingle resource to the nutrient and water balance of multiple species of different body sizes,foraging modes and dietary guilds in any ecosystem. This work should also provide importantnew empirical evidence on how home range size and foraging mode affect individualexploitation of a resource system.Finally, this research will bring all facets of the scientific process to a large number ofgraduate and undergraduate students. Twenty undergraduate students and 1 graduate student willobtain extensive research experience working on this project and it is likely that many more willbe trained through the REU program. This research is bound to have a major inpact with thepublic as well, because of my association with the Arizona-Sonora Desert Museum. Researchresults from this project will be the basis of a centerpiece display at the museum that explores thescientific process and the interactions of saguaros with the other inhabitants of the SonoranDesert.