Behaviorally mediated indirect species interactions in a subtropical seagrass community

大型海洋脊椎动物栖息地利用的功能知识对于理解许多海洋群落的结构和动态至关重要。例如，食草脊椎动物可以大大改变海草的物种组成和生物量，这可能反过来影响许多其他海洋物种。大型捕食者也可能通过直接和间接途径在构建海洋群落中发挥重要作用。亚致死捕食者效应，如诱导选择低风险栖息地进行觅食，或在风险高时降低觅食率，可能对猎物种群产生重要影响，与致死效应相当，甚至超过致死效应。重要的是，这些捕食者的亚致死效应可以超越其行为所影响的猎物物种，从而产生行为介导的间接物种相互作用（BMII）。虽然BMII已经在中生态实验中进行了研究，但迫切需要在复杂群落中收集现场数据，以充分了解这些现象的性质和重要性，特别是在海洋群落中。本项目将调查可能影响亚热带海草群落结构的潜在生物多样性指数。虎鲨（Galeocerdo cuvier）是否会对海草群落产生非致命的间接影响，这些影响是由海草群落中最大的食草动物儒艮（Dugong dugon）对捕食风险敏感的觅食行为介导的？初步证据表明，儒艮对鲨鱼捕食的风险有反应，在其他地方的研究表明，儒艮可以影响海草群落。这项研究将在西澳大利亚的鲨鱼湾进行，那里有世界上最大和最安全的儒艮种群之一，儒艮经常在温带物种的海草群落中觅食。虎鲨在海湾中数量极其丰富，且数量呈现出相当大的时空变化。捕食风险的变化模式和海草生物量和质量的调查将用于研究能量（或营养物质）的可得性和捕食风险如何影响儒艮的生境和微生境的利用，以及它们的觅食时间预算和能量和营养摄入率。虎鲨对海草群落的间接影响，以儒艮觅食为中介，将通过隔离和控制来确定，将儒艮和海龟放牧的影响分开，以及实验操作的影响。更广泛的影响：本研究将增强对BMII的总体理解及其在决定群落结构方面的作用，并为海洋群落中鲨鱼捕食风险和儒艮放牧的重要性提供见解。这个项目将是第一个明确解决大型鲨鱼在构建海洋群落中的作用的项目。本项目资助博士生1名，博士后1名。佛罗里达国际大学（Florida International University）是一所为少数族裔服务的大学，许多本科生也将参与该领域和实验室的研究。本科生也将从俄亥俄州和密歇根州的小型文理学院招募。最后，结果将通过网站、电视纪录片和公开演讲向公众传播。

A functional knowledge of habitat use by large marine vertebrates may be critical forunderstanding the structure and dynamics of many marine communities. For example, grazing vertebrates can substantially alter species composition and biomass of seagrasses, which may in turn affect many other marine species. Large-bodied predators also may be important in structuring marine communities, through direct and indirect routes. Sub-lethal predator effects, such as induced selection of low-risk habitats for foraging, or reduced foraging rates when risk is high, may have important implications for prey populations, rivaling or even exceeding those of lethal effects. Importantly, these sub-lethal effects of predators can transcend the prey species whose behavior they affect, thereby creating behaviorally-mediated indirect species interactions (BMII). While BMII have been studied in mesocosm experiments, there exists a critical need to gather field data in complex communities to fully understand the nature and importance of these phenomena, particularly in marine communities. This project will investigate a potential BMII that may influence the structure of a subtropical seagrass community. Do tiger sharks (Galeocerdo cuvier) have non-lethal indirect effects on seagrass communities mediated by predation-risk sensitive foraging by dugongs (Dugong dugon), the community's largest grazer? Preliminary evidence shows that dugongs respond behaviorally to shark predation risk, and studies in other locations have shown that dugongs can impact seagrass communities. This study will be undertaken in Shark Bay, Western Australia, which contains one of the world's largest and most secure dugong populations, and where dugongs routinely forage in seagrass communities with temperate species. Tiger sharks are extremely abundant in the bay and show considerable spatial and temporal variation in abundance. Patterns of variation in predation risk and surveys of seagrass biomass and quality will be used to address how energy (or nutrient) availability and predation risk influence habitat and microhabitat use of dugongs, as well as their foraging time budgets and energy and nutrient intake rates. Indirect effects of tiger sharks on seagrass communities, mediated by dugong foraging, will be determined using exclosures and controls that separate the impacts of dugong and sea turtle grazing as well as the effects of experimental manipulations.Broader Impacts: This study will enhance an understanding of BMII in general and their role in determining community structure as well as offer insights into the importance of shark predation risk and dugong grazing in marine communities. This project will be the first to explicitly address the role of a large shark in structuring a marine community. This project will fund a PhD student and a postdoctoral investigator. Many undergraduates will also be involved, in the field and the laboratory, from Florida International University, a minority-serving institution. Undergraduates will also be recruited from small liberal arts colleges in Ohio and Michigan. Finally, results will be disseminated to the public through a website, television documentaries, and public talks.