Impacts of altered rainfall predicted by climate-change models on the arthropod community, litter decomposition, and trophic cascades in a forest-floor food web.

摘要

Global climate-change models predict changes in the amount of precipitation. In the forest-floor food web, the arthropod community, litter decay, and trophic cascades, or indirect effects of predators on lower trophic levels, could all be impacted by altered rainfall. I conducted field experiments using plots located in two forest sites to examine the impacts of both an increase and decrease in rainfall on this system while also monitoring ambient plots.; In the first experiment, investigated the community-level response of leaf-litter arthropods to altered rainfall over three field seasons by periodically estimating arthropod densities. A multivariate technique demonstrated that altered rainfall led to shifts in arthropod community structure. The community responded in a complex manner with some taxa responding strongly to rainfall treatment, some showing no response, and some responding in only one of the two sites. The results suggest that bottom-up processes (i.e. control by the resource base) are important in this detrital system. However, top-down processes (i.e. predation) and competition among individuals within a trophic level also appear to influence this community.; In a second experiment, I investigated the impacts of altered rainfall on litter decay and on faunal impacts on decay using litterbags of different mesh sizes. Litter in the high-rainfall and ambient plots decayed 50% and 78% faster, respectively, than litter in the low-rainfall plots. Litter in the ambient plots disappeared 20% faster than litter in the high-rainfall plots. Thus, litter decay is strongly impacted by the amount, and possibly intensity, of rainfall. Surprisingly, arthropods had little impact on decay rate regardless of rainfall treatment.; In a third experiment,{09}tested the hypothesis that trophic cascades, specifically the indirect effect of spiders on leaf-litter decay, would be altered by rainfall regime. Within the experimental plots, I established small natural-spider density and low-spider density plots containing litterbags. Spiders accelerated litter disappearance under low rainfall (ca. 20% faster decay in natural-spider than in low-spider plots), but had little, or possibly a negative, effect under high rainfall.; Overall, this research demonstrates that altered rainfall of the magnitude predicted by climate-change models can impact the structure of the arthropod community, the process of litter decay, and trophic cascades in this detrital system.