Evol Ecol Res 4: 719-736 (2002)     Full PDF if your library subscribes.

Evolutionary dynamics of frequency-dependent growth strategy in cannibalistic amphibians

J.Y. Wakano,* Y. Kohmatsu and N. Yamamura

Centre for Ecological Research, Kyoto University, Kamitanakami Hiranocho, Otsu, Shiga 520-2113, Japan

Address all correspondence to Joe Yuichiro Wakano, Department of Chemical System Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.
e-mail: joe@chemsys.t.u.-tokyo.ac.jp


Cannibalistic amphibian larval morphs, which have greater head widths than typical morphs and therefore have larger mouths, provide the basis for the construction of a simple model of cannibalism that describes the growth dynamics of body shape. As the relative head sizes of interacting individuals determine the occurrence of cannibalism, the situation is frequency-dependent. Because natural enemies prey more often upon individuals with a more unbalanced body shape, an optimal growth schedule should exist. The necessary conditions for an evolutionarily stable strategy (ESS) are derived analytically; these conditions are checked by evolutionary simulation. When the probability of cannibalism is low, an ESS exists. In such cases, the body shape is more balanced (less adaptive to cannibalism) when predation pressure is higher and population density is lower. When the probability of cannibalism is high, there is no ESS. For such cases, a computer simulation of the evolutionary dynamics revealed that the dominant growth strategy changes cyclically. The development of a more detailed model of individual-based population dynamics showed that the qualitative results of the simple model held for the individual-based model. Accompanied by cyclic evolution, the number of surviving individuals at metamorphosis oscillated. The frequency-dependent models suggested that the evolutionary dynamics of cannibalism change dramatically depending upon environmental conditions.

Keywords: cannibalism, cannibalistic morph, evolutionary cycling, evolutionary dynamics, frequency dependence, polymorphism.

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