Kurle et al 2008 Rats(1)

Kurle et al 2008 Rats(1) - Introduced rats indirectly...

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Introduced rats indirectly change marine rocky intertidal communities from algae- to invertebrate-dominated Carolyn M. Kurle*, Donald A. Croll, and Bernie R. Tershy Department of Ecology and Evolutionary Biology, University of California, 100 Shaffer Road, Santa Cruz, CA 95060 Communicated by Donald Kennedy, Stanford University, Stanford, CA, January 22, 2008 (received for review September 10, 2007) 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 densi- ties and marine rocky intertidal community structures through sur- veys 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 Feshy algal cover was reduced. Our results demonstrate that invasive rats directly reduce bird densities through predation and signi±cantly affect in- vertebrate and marine algal abundance in the rocky intertidal indi- rectly via a cross-community trophic cascade, unexpectedly changing the intertidal community structure from an algae- to an invertebrate- dominated system. community structure u invasive species u Rattus norvegicus u trophic cascade u marine birds H airston et al. (1) laid the theoretical framework for the role of trophic interactions in structuring ecological communi- ties, whereby carnivores keep herbivores in check via predation that releases plants from heavy grazing pressure, thus resulting in a ‘‘green world.’’ As a result of their article and other seminal publications on the topic, much attention in community ecology has focused on the role of predators in structuring communities. Thus, the direct and indirect effects of top-level predators on community composition have repeatedly been demonstrated at the population or community level, but landscape-level illustra- tions of communities transformed by top predators via trophic cascades are still scarce (but see refs. 2–4). Vertebrate predators introduced to oceanic islands throughout an archipelago provide ecologists with opportunities to investigate the presence and extent of such cascades over larger spatial scales. Studies of
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This note was uploaded on 11/22/2011 for the course BIO 171 taught by Professor Josephinekurdziel during the Fall '08 term at University of Michigan.

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Kurle et al 2008 Rats(1) - Introduced rats indirectly...

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