Density vs. Trait-Mediated Interactions Between Predators and Prey: Their Influence on Rocky Shore Algal Diversity and Community Structure

营养级联概念深刻地提高了我们对捕食者-猎物相互作用如何塑造生态群落结构和多样性的理解。营养级联研究通常关注捕食者对猎物密度的影响如何通过食物链传播，从而形成物种多样性和群落结构（即密度介导的间接相互作用）。最近，人们对相互作用的改变越来越感兴趣：系统中第三种物种（捕食者）的存在改变了其他两个物种（猎物和它们的资源）之间的相互作用。性状介导的间接相互作用（TMIIs）是由于捕食者对猎物性状而不是猎物密度的影响而发生的相互作用。例如，在水生系统中，水生捕食者的风险线索可以引起猎物行为的变化，例如摄食率，从而改变猎物。S对低营养层的影响。因此，TMIIs强调非致命的捕食者效应，而不是更普遍强调致命的间接效应（DMIIs）。尽管生态学家开始认识到tmii的重要性，但对于控制密度和性状介导的捕食者效应的相对重要性以及它们如何塑造生态群落的多样性和结构的因素，人们的理解仍然有限。关于食草蜗牛对岩石海岸大型藻类群落的多样性和结构的重要性的经典工作留下了持久的印象。Luchenco证明了这些群落的多样性和演替与蜗牛（Littorina littorea）密度密切相关，并且这种关系的功能本质在潮汐池和新兴基质之间是不同的。此外，她假设绿蟹（Carcinus maenas）的捕食可能通过调节L. littorea的密度对藻类群落产生间接影响。这个假设在概念上很有吸引力，但20多年过去了，它没有得到实验验证。最近的数据表明，绿蟹风险提示对蜗牛放牧的抑制可以对岩岸藻类群落产生重大影响。本研究通过提出以下问题，探讨了密度和特性介导的绿蟹与L. littorea之间的相互作用对岩石海岸藻类多样性和结构模式的相对重要性：什么因素决定了密度和性状介导效应的相对重要性？——二世。dmii和tmii的相对重要性如何影响岩石潮间带海岸的长期藻类多样性和群落结构？——第三。dmii和tmii相对重要性的栖息地特异性差异能否解释两种突出的岩岸栖息地（涌出基质和潮池）中藻类多样性和蜗牛密度之间功能关系的差异？这项研究将通过明确地研究高阶相互作用在塑造长期社区动态中的作用，对实证和理论生态学产生广泛的影响。通过在一个系统中工作(a)被广泛认为是密度介导效应作用的经典示范，(b)对现代生态学的发展做出了重大贡献，拟议的研究将更好地理解形成岩石海岸和其他社区多样性和结构的过程。因为这些食物链相对简单且容易操纵，这些栖息地为探索这些问题提供了绝佳的机会。

The trophic cascade concept has profoundly improved our understanding of how predator-prey interactions shape the structure and diversity of ecological communities. Trophic cascade studies typically focus on how predator effects on prey density propagate through food chains to shape species diversity and community structure (i.e., Density-Mediated Indirect Interactions). Recently, there has been growing interest in interaction modifications: the presence of a third species (predator) in the system alters the interaction between two other species (prey and their resource). Trait-Mediated Indirect Interactions (TMIIs) are those that occur because of predator effects on prey traits rather than prey density. For example, in aquatic systems water-borne predator risk cues can induce changes in prey behavior, such as feeding rates, thus altering the prey.s impact on lower trophic levels. Hence, TMIIs emphasize nonlethal predator effects in contrast to the more prevalent emphasis on lethal indirect effects (DMIIs). Although ecologists are beginning to appreciate the importance of TMIIs, there is still a limited understanding of the factors governing the relative importance of density and trait-mediated predator effects and how they shape the diversity and structure of ecological communities. Classic work on the importance of herbivorous snails to the diversity and structure of macro-algal communities on rocky shores has left a lasting impression. Luchenco demonstrated that diversity and succession in these communities is closely tied to snail (Littorina littorea) density and that the functional nature of this relationship differs between tidal pools and emergent substrata. Moreover, she hypothesized that green crab (Carcinus maenas) predation may exert an indirect influence on algal communities by regulating L. littorea density. This hypothesis is conceptually appealing, but over 20 years have passed without it being tested experimentally. Recent data suggest that the suppression of snail grazing by green crab risk cues can have a significant effect on rocky shore algal communities. This research examines the relative importance of density and trait-mediated interactions between green crabs and L. littorea to patterns of algal diversity and structure on rocky shores by asking the following questions: --I. What factors shape the relative importance of density and trait-mediated effects? -- II. How may the relative importance of DMIIs and TMIIs influence long-term algal diversity and community structure on rocky intertidal shores? -- III. Can habitat-specific differences in the relative importance of DMIIs and TMIIs explain differences in the functional relationship between algal diversity and snail density in two prominent rocky shore habitats: emergent substrata and tide pools? This research will have broad implications to empirical and theoretical ecology by explicitly examining the role higher order interactions play in shaping long term community dynamics. By working in a system (a) widely held as a classic demonstration of the role of density-mediated effects and (b) that has contributed significantly to the development of modern ecology, the proposed research will provide a better understanding of the processes shaping diversity and structure in rocky shore and other communities. Because these food chains are relatively simple and easily manipulated, these habitats afford an excellent opportunity to explore these issues.