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Effects of crayfish on leaf processing and invertebrate colonisation of leaves in a headwater stream: decoupling of a trophic cascade

Oecologia (Impact Factor: 3.25). 09/2000; 124(4):608-614. DOI: 10.1007/s004420000422

ABSTRACT I performed a field experiment to test the hypothesis that omnivorous crayfish both promote the breakdown of leaves (basal resources) and decouple any potential trophic cascade by similtaneously affecting intermediate consumers as well as there basal resource. Leaf packs were placed inside in situ artificial channels, which excluded or allowed access to crayfish.. During a 4 week period, crayfish greatly promoted leaf processing, with decomposition rates among the fastest ever recorded from temperate streams. Crayfish also affected invertebrate abundance in the leaf packs. As a result of resource consumption, predation and bioturbation, crayfish treatments contained significantly lower densities of invertebrates. In contrast, exclusion of crayfish did not promote leaf decay via increased colonisation by detritivores, primarily because of the conspicuous lack of shredder insects in New Zealnd streams. The results support the hypothesis that omnivorous top consumers decouple cascading chains through similtaneous direct and indirect effects on intermediate consumers and basal resources. Decapod consumers, which have largely been ignored in leaf decomposition studies, can be key leaf processorsin temperate streams where shredder insects are poorly represented.

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    • "If an introduced species can occupy a wider trophic niche than a native species it replaces, this may not only enable it to be successful but may mean its establishment alters food web structures in the ecosystem. Freshwater crayfish are often considered keystone species in freshwater ecosystems and hence in food webs (Momot 1995; Nyström et al. 1996, 1999; Usio 2000). Crayfish feed on benthic invertebrates, macrophytes , algae, detritus, and fish carcases and eggs (Whitledge and Rabeni 1996, 1997; Stenroth and Nyström 2003), and are themselves eaten by larger animals (Roel and Orth 1993; Barrientos et al. 2013). "
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    • "However, in case of scarcity or absence of specialist shredders, organic matter breakdown can be driven by other invertebrates such as decapods [10, 14– 17] and gastropods [18] [19]. Concerning crayfish species few studies have been conducted to assess their role on riparian leaf processing (but see [10] [15] [17] [20] [21]). The red swamp crayfish Procambarus clarkii, a native species from northeastern Mexico and south central USA, has been introduced worldwide for commercial and recreational purposes. "
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