Effect of competitor abundance on feeding territoriality in a grazing fish,the ayuPlecoglossus altivelis |
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Authors: | Kei'ichiroh Iguchi Teruaki Hino |
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Institution: | (1) Ueda Station, National Research Institute of Fisheries Science, Komaki 1088, 316 Ueda, Nagano, Japan;(2) Forestry and Forestry Products Research Institute, Kansai Research Center, Momoyama, Fushimi, 612 Kyoto, Japan |
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Abstract: | The grazing fish, ayu,Plecoglossus altivelis Temminck & Schlegel, establishes feeding territorialiry during the young stage. The population density fluctuates from year
to year by more than a hundredfold, but the determinant of territory size is less well known. The feeding territoriality of
ayu was examined under simulated habitat conditions where fish density was manipulated and food resources were renewable.
Fish competed for algae attached to the substrata and were divided into residents with territories, and floaters without territories.
By experimental alteration of fish density the number of residents increased with density and rerritory size decreased with
density. Floaters intruded into territories in a school to feed on algae, which induced overt aggression of the resident and
reduced the productivity of algae growing there. Both the intruding frequency of floaters over territorial areas and their
feeding pressure on algae increased at higher floater density. Floaters functioned to shift cost-benefit relationships for
various territory sizes. They acted as food competitors to restrict territory size below a maximum through competitive interference.
Although the growth rate of residents was inversely related to fish density, residents grew faster than floaters in each group.
Under a given set of competitor abundances, economic defensibility determined territory size. |
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Keywords: | economic defensibility energy maximizer indeterminate growth resource renewability |
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