Influences of microhabitat use and foraging mode similarities on intra- and interspecific aggressive interactions in a size-structured stream fish assemblage |
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Authors: | Nisikawa Usio Shigeru Nakano |
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Institution: | (1) Biodiversity Group, Institute of Low Temperature Science, Hokkaido University, 060 Sapporo, Japan;(2) Present address: Department of Zoology, University of Otago, P. O. Box 56, Dunedin, New Zealand;(3) Tomakomai Research Station, Hokkaido University Forests, Aza-Takaoka, 053 Tomakomai, Japan |
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Abstract: | Aggressive interactions, foraging behaviour and microhabitat use were observed among four sympatric stream fishes inhabiting
the water column: ayu (Plecoglossus altivelis), white-spotted charr (Salvelinus leucomaenis), masu salmon (Oncorhynchus masou) and Japanese dace (Tribolodon hakonensis), each species being categorised into five body-size classes (species-size groups; SSG's). Aggressive interactions were observed
between most pairs of SSG's, an almost linear dominance order being apparent throughout the three-month study period. Ayu
were relatively subordinate in June, but became the second most dominant in July and the most dominant in August, as a consequence
of a reversal in dominance order with salmon. In contrast, smaller-sized dace, which continually suffered from intra- and
interspecific aggression, occupied the most subordinate ranks throughout the study period. Intensive aggression was observed
among various SSG's, exhibiting same microhabitat propensity throughout the three months. The direction and frequency of aggressive
interactions varied month by month due to a reversal in dominance order between ayu and masu salmon, and/or changes in density,
body size and resource use of the component members. Opponent selectivity was higher within SSG's, where resource use was
assumed to be highly overlapping, rather than among SSG's throughout the study period. Correlation analysis indicated that
opponent selectivity in aggressive interactions among SSG's was positively correlated with similarity in microhabitat selectivity
in June, but not in other months or with that in foraging habits, suggesting that intensive aggressive behaviour reflected
overlapping habitat use among assemblage members during a certain period. |
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Keywords: | Interference dominance hierarchy body size intra- and interspecific interactions |
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