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; 124:608-614. 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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