CAREER: Does predator intimidation help structure a pristine seagrass community through multiple indirect pathways?

最近的一项综合研究表明，放牧在海草生态系统中的作用通常被低估，通过长期的实验研究，我们对这些关键海洋群落的理解将大大增强，这些实验研究将确定多个行会的放牧的影响，特别是在大多数沿海系统中急剧减少的巨型食草动物（绿海龟、海螺）。此外，考虑到海洋捕食者数量的急剧下降，需要了解上层营养水平如何构成食草动物影响的时空格局，以便能够预测海洋环境的人为变化将如何影响海草生态系统。总体而言，群落生态学的预测框架一直受到阻碍，部分原因是捕食者的非致命影响，无论是直接的还是间接的，往往被忽视。行为介导的间接物种相互作用（BMII）发生在捕食者引起猎物的行为改变并传播到较低营养水平的情况下。虽然BMII在形成群落动态方面似乎很重要，但大多数关于BMII的研究都是在小规模实验中进行的，并且没有考虑到顶级捕食者可能启动多个BMII，这些BMII可能会减弱或放大它们在自然群落中的间接影响。在这项研究中，Heithaus博士将扩展之前对世界上最原始的海草生态系统之一（澳大利亚鲨鱼湾）的调查，以确定由虎鲨发起的多重BMII是否减弱或增强了它们对海草群落的间接影响。在之前nsf资助的研究中，结果表明虎鲨可以通过两条平行的非致命途径间接影响海草群落，而不仅仅是一条。在第一个完善的三步BMII中，虎鲨引起巨型食肉动物觅食地点的变化，当鲨鱼出现时，在危险的微栖息地保护海草。在第二种可能的BMII中，虎鲨引起了鱼食动物（海豚、鸬鹚）微栖息地使用的变化，这可能导致在巨型食肉动物放弃的微栖息地中食草鱼类的放牧增加。根据草食性鱼类与海草相互作用的性质，这些BMII可能导致虎鲨对海草群落的影响减弱或放大。在这份新合同中，进一步的监控视觉和视频调查、实验性草食试验、水下视频监控和海龟携带的视频摄像机将用于确定放牧的时空模式是否以及如何变化。将在实地进行实验，采用两种类型的封闭和海草移植，以确定虎鲨发起的BMII的相对重要性，以及它们是否会减弱或放大鲨鱼对海草群落的影响。该项目将支持对高度互动的海洋物种（鲨鱼、海龟、海牛）相对原始的群落进行一些最全面的长期研究，将数据集延长至15年。这将使Heithaus博士和合作者能够解决关于丰度模式如何受到大规模海洋学和气候因素影响的新问题。该项目还将制定一个广泛的教育和推广计划，并将其纳入研究计划。这包括:1) 5 -8年级生物教师在鲨鱼湾的研究经验，2)研究生与中学生的互动，3)研究生和PI在学校、地区和国家科学教师会议上的演讲，4)基于鲨鱼湾物种的课程计划的发展，5)中学课堂使用的dvd的发展，6)视频实验室的发展，7)国家地理在线和点播频道——NGC Wild的视频内容，8)为本科生和研究生提供研究经验，9)加强教育网站。

A recent synthesis suggests that the role of grazing in seagrass ecosystems is generally under-appreciated and that our understanding of these critical marine communities would be greatly enhanced by long-term experimental studies that determine the impact of grazing by multiple guilds, especially megagrazers (green turtles, sirenians) that have declined dramatically in most coastal systems. Furthermore, given the steep declines in populations of marine predators, an understanding of how upper trophic levels structure spatio-temporal patterns of grazer impacts is needed to be able to predict how anthropogenic changes to marine environments will influence seagrass ecosystems. A predictive framework of community ecology in general has been hampered in part because non-lethal effects of predators, both direct and indirect, often are overlooked. Behaviorally mediated indirect species interactions (BMII) occur when a predator causes a change in the behavior of its prey that is transmitted to lower trophic levels. While BMII appear to be important in shaping community dynamics, most studies of BMII have been carried out in small-scale experiments, and have not considered that top predators might initiate multiple BMII that could either attenuate or amplify their indirect effects in natural communities. In this study, Dr. Heithaus will expand on previous investigations on one of the world's most pristine seagrass ecosystems (Shark Bay, Australia) to determine whether multiple BMII initiated by tiger sharks attenuate or amplify their indirect effects on seagrass communities. During previous NSF-funded research, the results show that tiger sharks can indirectly influence seagrass communities through two parallel non-lethal pathways rather than just one. In the first, well-established three-step BMII, tiger sharks cause shifts in megagrazer foraging locations, shielding seagrasses in dangerous microhabitats when sharks are present. In a second possible BMII, tiger sharks cause shifts in piscivore (dolphin, cormorant) microhabitat use that could result in enhanced grazing by herbivorous fishes in the microhabitats that megagrazers have abandoned. Depending on the nature of herbivorous fish interactions with seagrasses, these BMII could result in attenuation or amplification of tiger shark impacts on seagrass communities. In this new award, further monitoring visual and video surveys, experimental herbivory trials, underwater video monitoring, and turtle-borne video cameras will be used to determine whether and how spatiotemporal patterns of grazing vary. Experiments, in the field, will be employed using two types of exclosure and seagrass transplants to determine the relative importance of the BMII initiated by tiger sharks and whether they result in attenuation or amplification of shark effects on seagrass communities. This project will support some of the most comprehensive long-term studies of a relatively pristine community of highly interactive marine species (sharks, turtles, sea cows), extending the datasets to 15 years. This will enable Dr. Heithaus and collaborators to address new questions about how patterns of abundance are influenced by large-scale oceanographic and climatic factors. The project will also develop a broad education and outreach program that is integrated into the research program. This includes: 1) 5th-8th grade biology teacher research experiences in Shark Bay, 2) graduate student interactions with middle school students, 3) talks by graduate students and the PI at schools and regional and national science teacher conferences, 4) the development of lesson plans based on species in Shark Bay, 5) the development of DVDs for use in secondary school classrooms, 6) the development of video labs, 7) video content for National Geographic's online and on-demand channel - NGC Wild, 8) research experiences for undergraduate and graduate students, and 9) the enhancement of an educational website.