TERRESTRIAL INVERTEBRATE INPUTS DETERMINE THE LOCAL ABUNDANCE OF STREAM FISHES IN A FORESTED HEADWATER STREAM.

Y. Kawaguchi¹, S. Nakano², and Y. Taniguchi³. ¹Aqua Restoration Research Center Government Land Reserve, Kasada, Kawashima, Gifu, 501-6021, Japan, ²Center for Ecological Research, Kyoto University, Hirano-cho, Kamitanakami, Otsu, Shiga, 520-2113, Japan, ³Department of Life Environmental Science, Yamaguchi Prefectural University, 3-2-1 Sakurabatake, Yamaguchi, Yamaguchi, 753-8502, Japan

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 explained by field experiment. We present experimental evidence that terrestrial invertebrate inputs directly influence on the distribution of stream fishes in a forested headwater stream. When terrestrial invertebrate input to the stream was experimentally reduced by using greenhouse-type covers, fish biomass also decreased dramatically. Despite the greater amounts of input in the control than in treatments, terrestrial invertebrates comprised approximately 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 evidence that the flow of such allochthonous resources in the donor-controlled system can be a key to elucidating the mechanisms of the distribution and dynamics of the consumer populations.