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Fish Predation on Bosmina longirostris: Body-Size Selection Versus Visibility Selection

Thomas M. Zaret and W. Charles Kerfoot
Ecology
Vol. 56, No. 1 (Winter, 1975), pp. 232-237
Published by: Wiley
DOI: 10.2307/1935317
Stable URL: http://www.jstor.org/stable/1935317
Page Count: 6
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Fish Predation on Bosmina longirostris: Body-Size Selection Versus Visibility Selection
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Abstract

We examine the effects of fish predation on a population of Bosmina longirostris (O. F. Müller), a smaller, limnetic cladoceran, in Gatun Lake, Panama. We test the relative importance of two different modes of predator selection: body-size selection, in which fish choose the largest of otherwise identically appearing individuals, and visibility selection, in which fish choose individuals having the greatest amount of body pigmentation. In B. longirostris, this pigmentation is most heavily concentrated in the large, black, compound eye of these otherwise transparent animals. We find that these predators are feeding according to visibility selection and that body-size selection is of negligible importance under these circumstances. We then discuss the general applicability of these findings, and the evolutionary consequences for prey populations under this type of selective pressure.

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