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The Adaptive Significance of Interspecific Territoriality in the Reef Fish Eupomacentrus Leucostictus

John Paul Ebersole
Ecology
Vol. 58, No. 4 (Jul., 1977), pp. 914-920
Published by: Wiley
DOI: 10.2307/1936228
Stable URL: http://www.jstor.org/stable/1936228
Page Count: 7
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The Adaptive Significance of Interspecific Territoriality in the Reef Fish Eupomacentrus Leucostictus
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Abstract

Observations were made on the fishes trespassing in 50 territories of the reef pomacentrid Eupomacentrus leucostictus, and on the responses of the territory-holders to the trespassers. The extent to which each of the tresspasser species elicited agonistic responses from territorial E. leucostictus individuals was quantified: number agonistic acts/total trespass time. Using data on feeding habits, the diet overlap of each trespassing species on E. leucostictus was computed according to the formula @a = @Sp"i"hP"j"h/@SP"i"h^2. Following a log-log transformation to correct for heteroscedasticity, a Pearson product-moment correlation between number gonistic acts/total trespass time revealed a significant positive correlation between these 2 variables. An expression for Potential Competitive Impact that combines trespasser size with diet overlap, @a(V"B)^7^5, showed a highly significant correlation with number agonistic acts/total trespass time (again using a log-log transformation) and a higher correlation coefficient (r =.613, P<.01). When this correlation was recalculated with the exclusion of the 9 trespassing species known to eat eggs, the correlation coefficient improved to r =.744, P <.01. These 9 egg-eating species have a significantly greater tendency to elicit agonism beyond that expected on the basis of their Potential Competitive Impact than do the other tresspassing species. (t =2.940, P <.02). This pattern of agonism indicates that interspecific territoriality is an adaptive behaviorthat reduces the loss of food in the territory to competitors and protects the nest from egg predators.

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