Terrestrial invertebrate inputs determine the local abundance of stream fishes in a forested stream

Abstract

Transfer of energy from more productive donor habitats is frequently significant for the maintenance of consumers in the recipient habitats. Nevertheless, the connection between the distribution of consumers and allochthonous inputs has not been directly examined by field experiment. We present experimental evidence that terrestrial invertebrate inputs directly influence the distribution of stream fishes in a forested headwater stream. When terrestrial invertebrate input to the stream was experimentally reduced by using greenhouse covers, fish biomass also decreased dramatically. Despite the greater amounts of input in the control than in the reduced treatments, terrestrial invertebrates made up ∼90% of stomach contents in both treatments during the study period. Moreover, no difference in fish growth rates was evident between the treatments. These results provide experimental evidence that the flow of such allochthonous resources in the donor-controlled system can explain the distribution and dynamics of the consumer populations.