Unexpected Discontinuities in Life-History Evolution under Size-dependent Mortality

Taborsky, B., Dieckmann, U. ORCID: https://orcid.org/0000-0001-7089-0393, & Heino, M. ORCID: https://orcid.org/0000-0003-2928-3940 (2003). Unexpected Discontinuities in Life-History Evolution under Size-dependent Mortality. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-03-004

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Abstract

In many organisms survival depends on body size. We investigate the implications of such size-selective mortality on life-history evolution by introducing and analyzing a new and particularly flexible life-history model with the following key features: the lengths of growth and reproductive periods in successive reproductive cycles can vary evolutionarily, the model does not constrain evolution to patterns of either determinate or indeterminate growth, and lifetime number and sizes of broods are the outcome of evolutionarily optimal life-history decisions. We find that when size-dependent mortality is sufficiently strong, small changes in environmental conditions can lead to abrupt transitions in optimal life histories. Such discontinuous switching results from antagonistic selection pressures and occurs between strategies of early maturation with short reproductive periods and late maturation with long reproductive cycles. When mortality size-selective and the size-dependent component is not too high, selection favors prolonged juvenile growth, thus allowing individuals to reach a mortality refuge at large body size before the onset of reproduction. When either component of mortality is then increased, the mortality refuge first becomes unattractive and eventually closes up altogether, resulting in short juvenile growth and frequent reproduction. Our results offer a new mechanism for the evolution of life-history dimorphism.

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