Evol Ecol Res 2: 565-582 (2000)     Full PDF if your library subscribes.

Adaptive strategies in size-structured populations: Optimal patterns and perturbation analysis

Maria-Josefina Hernandez and Jesús Alberto León

Laboratorio de Biología Teórica, Instituto de Zoología Tropical, Facultad de Ciencias, Universidad Central de Venezuela, Apartado 47058, Caracas 1041-A, Venezuela

Author to whom all correspondence should be addressed.
e-mail: mjhernan@strix.ciens.ucv.ve


In some species of plants, fish and invertebrates, life histories are best classified according to size. The probability of surviving, and of growing or staying in the same stage, are size-dependent. So is fecundity for adult females. Trade-offs exist between these traits due to finite energy availability; these constrain the maximization of fitness. The optimization model developed here predicts the occurrence of life cycles of individuals with determinate and indeterminate growth, based on its actual pattern of size-specific reproductive values. A perturbation analysis is performed to evaluate the direction of change in optimal phenotypes when mortality factors, specific to a given size class, increase. The model predicts that natural selection favours an extra investment of energy in growth and fecundity during the affected stage if the mortality factor perturbed is unavoidable, or an extra investment in protection if it is avoidable. For all other stages, the response depends on patterns of energy allocation before perturbation. Strategies for sizes smaller than the one where perturbation occurs are opposite to strategies in the larger ones.

Keywords: avoidable and unavoidable mortality, constrained optimization, life-history evolution, perturbation analysis, reproductive values, size-structured populations.

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