Kelp forest community resilience in action: adaptive responses of predators to a disease-driven food web perturbation

生态学的一个关键目标是了解物种间的相互作用--竞争、捕食、互利共生--如何影响结构（例如，生物多样性）和功能（例如，生产力），并有助于生态系统的稳定和复原力。沿着北美西海岸的海带森林一直是海洋生态学家探索这些问题的模范生态系统。这项工作提供了证据，表明包括海獭、海星和鱼类在内的捕食者在控制海胆方面可能很重要，否则海胆会过度放牧森林，并创造出替代的“贫瘠”状态，没有海藻。然而，其他的例子表明，疾病和干扰，而不是捕食者，抑制海胆过度放牧。在这里，我们采用实验和调查，以确定是否以及如何海獭和海星单独和联合行动，以控制海胆种群的快速增长，发生在演唱会与海星星“浪费”流行病沿着北美西海岸。这项工作的结果将（i）推进我们对多种捕食者如何相互作用以影响群落结构，稳定性和恢复力的理解，以及（ii）阐明物种相互作用如何有助于这些森林的稳定性，这些森林是生产性商业和休闲渔业的基础。该项目将涉及公民科学家参与海獭丰度，觅食行为和饮食的调查，以及代表性不足（主要是拉丁裔）的本科生，结果将在几个公共宣传设施和K-12教育计划中传播。该项目将促进我们对物种多样性和捕食者在促进群落结构稳定性和恢复力方面的综合作用的理解。虽然捕食者和多样性一直是许多研究的重点，但很少有人探讨捕食者多样性如何增强或不增强海洋生态系统的恢复力。研究人员将确定南部海獭（Enyhda lutris lutris）和两种海星（Pycnopodia helianthoides和Pisaster luteus）在控制两种猎物物种的密度和大小结构方面的相对贡献，紫色海胆（Strongylocentrotus puratus）和蜗牛（Promartynia pulligo），以及对巨型海带（Macrocystis pyrifera）的生存和密度的级联效应。正交操纵的捕食者访问在大型领域的外壳/外壳将被用来评估冗余，互补性和“抽样效应”（即特别重要的两个物种）之间的两个捕食者的直接死亡率和间接（性状介导）觅食行为的猎物的相对作用。研究人员将评估实验结果是否“扩大”，以解释捕食者（水獭和海星）、猎物（海胆）和主要初级生产者（巨型海藻）相对密度的地理差异，以及海獭补偿海星减少的能力，以控制紫色海胆种群的快速增长，否则会导致这些生态系统的相移（森林变成贫瘠）。

A key goal of ecology is to understand how species interactions -- competition, predation, mutualism -- influence the structure (e.g., biodiversity) and functions (e.g., productivity) of ecological communities and contribute to the stability and resilience of ecosystems. Kelp forests along the West Coast of North America have been a model ecosystem in which marine ecologists have explored these questions. That work has provided evidence that predators, including sea otters, sea stars, and fishes, can be important in controlling sea urchins that otherwise overgraze forests and create alternative "barrens" states, devoid of kelp. However, other examples suggest that disease and disturbance, not predators, suppress urchin overgrazing. Here we employ experiments and surveys to determine whether and how sea otters and sea stars act separately and in combination to control the rapid growth of sea urchin populations that is occurring in concert with a sea star "wasting" epidemic along the West Coast of North America. The results of this work will (i) advance our understanding of how multiple predators interact to influence community structure, stability and resilience, and (ii) shed light on how species interactions contribute to the stability of these forests that are the foundation of productive commercial and recreational fisheries. The project will involve citizen scientists contributing to surveys of sea otter abundance, foraging behavior and diet, and underrepresented (largely Latino) undergraduates and results will be disseminated in several public outreach facilities and K-12 educational programs. This project will advance our understanding of the combined roles of species diversity and predators in contributing to the stability and resilience of community structure. Though both predators and diversity have been the focus of numerous studies, fewer have explored how predator diversity does or does not enhance the resilience of marine ecosystems. The investigators will determine the relative contributions of southern sea otters (Enyhda lutris lutris) and two species of sea stars (Pycnopodia helianthoides and Pisaster giganteus) in controlling the density and size structure of two prey species, the purple sea urchin (Strongylocentrotus purpuratus) and a snail (Promartynia pulligo), and the cascading effects on survival and density of giant kelp (Macrocystis pyrifera). Orthogonal manipulations of predator access in large field enclosures/exclosures will be used to assess the relative roles of redundancy, complementarity and "sampling effect" (i.e. particular importance of either species) among the two predators on both direct mortality and indirect (trait-mediated) foraging behavior of their prey. The PIs will evaluate whether results from the experiments "scale up" to explain geographic variation in the relative densities of predators (otters and stars), prey (urchins) and the major primary producer (giant kelp) and the ability of sea otters to compensate for declines in sea stars to control the rapid growth in purple sea urchin populations that can otherwise cause phase shifts (forests to barrens) of these ecosystems.