Diel changes in resource use and diet overlap in temperate stream fishes
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Interspecific variation in diel-scale temporal niches is common in natural communities. Such variation changes population dynamics via effects on the growth and reproduction of individuals. Also at the community level, theory predicts that animals can reduce competition for shared resources by changing diel activity in certain situations. However, the role of diel activity at the community-level has not been examined sufficiently. In this study, to examine whether the diel-scale temporal niche act as a competition-mitigating mechanism for stream fishes at the community level, we surveyed diel changes in microhabitat use and foraging, and the pattern of interspecific diet overlap in the middle reaches of a temperate stream where various fish species that seemed to be either nocturnal or diurnal coexisted. Our results suggest that the fishes forage during both daytime and night, but change their foraging mode at different times of the day, so that the foraging habits of these fish species cannot be divided simply into nocturnal and diurnal. Furthermore, fishes appeared to aggregate in the vicinity of common food resources during time zones with high availability of the resources, and therefore, inter-guild diet overlap was high during certain time zones. On the other hand, when inter-guild diet overlap was low, each fish species used foods or microhabitats that did not any have the potential to be used by species of another guild. Therefore, we conclude that variation in diel niche use is influenced by variation in the fundamental niche and food supply or availability rather than by competitive interaction between fishes in the stream fish community.
KeywordsTemporal niche Diel change Nocturnal and diurnal Stream fish Stream community
Katsutoshi Watanabe of Kyoto University provided valuable comments on the manuscript. We thank Michio Hori, Teiji Sota and other members of Kyoto University for many helpful comments. We thank the staff of Ashiu Forest Research Station, Field Science Education and Research Center of Kyoto University, Kyoto, Japan, the staff of Miyama Gyokyo (Fisheries Cooperative of Miyama, Yura River), Kyoto, Japan and the local people of Ashiu, Miyama-cho, Kyoto, Japan for providing facilities. This study was supported by the Kansai Organization for Nature Conservation (KONC) and Global COE Program A06 ‘Formation of a Strategic Base for Biodiversity and Evolutionary Research: from Genome to Ecosystem’ from the Ministry of Education, Culture, Sports and Technology, Japan.
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