Kurle Carolyn M, Croll Donald A, Tershy Bernie R
Department of Ecology and Evolutionary Biology, University of California, 100 Shaffer Road, Santa Cruz, CA 95060, USA.
Proc Natl Acad Sci U S A. 2008 Mar 11;105(10):3800-4. doi: 10.1073/pnas.0800570105. Epub 2008 Feb 28.
It is widely recognized that trophic interactions structure ecological communities, but their effects are usually only demonstrated on a small scale. As a result, landscape-level documentations of trophic cascades that alter entire communities are scarce. Islands invaded by animals provide natural experiment opportunities both to measure general trophic effects across large spatial scales and to determine the trophic roles of invasive species within native ecosystems. Studies addressing the trophic interactions of invasive species most often focus on their direct effects. To investigate both the presence of a landscape-level trophic cascade and the direct and indirect effects of an invasive species, we examined the impacts of Norway rats (Rattus norvegicus) introduced to the Aleutian Islands on marine bird densities and marine rocky intertidal community structures through surveys conducted on invaded and rat-free islands throughout the entire 1,900-km archipelago. Densities of birds that forage in the intertidal were higher on islands without rats. Marine intertidal invertebrates were more abundant on islands with rats, whereas fleshy algal cover was reduced. Our results demonstrate that invasive rats directly reduce bird densities through predation and significantly affect invertebrate and marine algal abundance in the rocky intertidal indirectly via a cross-community trophic cascade, unexpectedly changing the intertidal community structure from an algae- to an invertebrate-dominated system.
人们普遍认识到营养相互作用构建了生态群落，但其影响通常仅在小尺度上得到证明。因此，改变整个群落的营养级联反应在景观尺度上的记录很少。动物入侵的岛屿提供了自然实验机会，既可以测量大空间尺度上的一般营养效应，也可以确定入侵物种在本地生态系统中的营养作用。研究入侵物种的营养相互作用最常关注其直接影响。为了研究景观尺度上营养级联反应的存在以及入侵物种的直接和间接影响，我们通过对整个1900公里长的群岛上有鼠岛和无鼠岛进行调查，研究了引入阿留申群岛的挪威鼠（褐家鼠）对海鸟密度和海洋岩石潮间带群落结构的影响。在无鼠岛上，在潮间带觅食的鸟类密度更高。有鼠岛上的海洋潮间带无脊椎动物更为丰富，而肉质藻类覆盖度则降低。我们的结果表明，入侵鼠通过捕食直接降低鸟类密度，并通过跨群落营养级联反应间接显著影响岩石潮间带无脊椎动物和海藻的丰度，意外地将潮间带群落结构从以藻类为主的系统转变为以无脊椎动物为主的系统。
