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

最近的一项综述表明，放牧在海草生态系统中的作用普遍被低估，长期的实验研究将极大地加强我们对这些关键海洋群落的了解，这些研究确定了多个行会放牧的影响，特别是在大多数沿海系统中急剧下降的大型捕食者(绿海龟、西里昂)。此外，鉴于海洋捕食者数量急剧下降，需要了解上层营养水平如何构成食草动物影响的时空模式，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。群落生态学的总体预测框架一直受到阻碍，部分原因是捕食者的非致命性影响，无论是直接的还是间接的，往往被忽视。行为中介的间接物种相互作用(BMII)发生在捕食者使其猎物的行为发生变化并传播到较低的营养水平时。虽然BMII似乎在塑造群落动态方面很重要，但大多数对BMII的研究都是在小规模实验中进行的，没有考虑到顶级捕食者可能会启动多个BMII，从而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)的研究，以确定由虎鲨引发的多个BMII是否减弱或放大了它们对海草群落的间接影响。在之前由NSF资助的研究中，研究结果表明，虎鲨可以通过两条平行的非致命性途径间接影响海草群落，而不是只有一条。在第一个公认的三步BMII中，虎鲨导致巨型捕食者觅食地点的转移，当鲨鱼存在时，在危险的微生境中保护海草。在第二个可能的BMII中，虎鲨引起了鱼类(海豚、鹈鹕)微生境使用的变化，这可能导致大型捕食者已经放弃的微生境中草食性鱼类的捕食增加。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。在这个新的奖项中，将使用进一步的监测视觉和视频调查、实验草食试验、水下视频监测和海龟携带的摄像机来确定放牧的时空模式是否以及如何变化。在野外，将使用两种类型的围栏和海草移植进行实验，以确定虎鲨引发的BMII的相对重要性，以及它们是否会导致鲨鱼对海草群落的影响减弱或放大。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的一些最全面的长期研究，将数据集延长到15年。这将使Heithaus博士和他的合作者能够解决大规模海洋和气候因素如何影响物种丰度模式的新问题。该项目还将开发一个广泛的教育和推广计划，并将其整合到研究计划中。这包括：1)鲨鱼湾5-8年级生物教师的研究经验，2)研究生与中学生的互动，3)研究生和PI在学校以及地区和国家科学教师会议上的演讲，4)根据鲨鱼湾的物种制定教案，5)开发用于中学课堂的DVD，6)开发视频实验室，7)为国家地理的在线和点播频道NGC Wild提供视频内容，8)本科生和研究生的研究经验，9)教育网站的增强。

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.