Evol Ecol Res 4: 169-179 (2002)     Full PDF if your library subscribes.

Semelparity versus iteroparity and the number of age groups

Veijo Kaitala,1,2* David Tesar1 and Esa Ranta1

1Integrative Ecology Unit, Division of Population Biology, Department of Ecology and Systematics, University of Helsinki, PO Box 17, Arkadiankatu 7, FIN-00014 Helsinki and 2Department of Biological and Environmental Science, University of Jyväskylä, PO Box 35, FIN-40351 Jyväskylä, Finland

Address all correspondence to Veijo Kaitala, Division of Population Biology, University of Helsinki, PO Box 17, FIN-00014 Helsinki, Finland.
e-mail: vkaitala@cc.jyu.fi


The perennial question in life-history evolution is the difference in fitness to reproduce only once (semelparity, S) or more than once (iteroparity, I) per lifetime. It is frequently argued that semelparous individuals can achieve a higher reproductive output by trading off longevity for fecundity. Along the same lines, it could be stated that iteroparous breeders have lower reproductive output because they are allocating some of the resources to survival in the year(s) to come. To us, the classical life-history question is confounded by the number of age groups. In the evolutionary literature, semelparity is often equated with annual life history and iteroparity with perennial life history (in plants). Here, we disentangle the number of age groups from the life-history question by using a Leslie matrix approach. Invasion analyses show that, given equal numbers of age groups (kS = kI) and letting the geometric rates of increase λS and λI to range from 1 to 5, the parameter space is generous enough to allow either of the life histories to be an evolutionarily stable strategy, the two life histories can co-exist, or both may go extinct. Letting kS ≠ kI does not rescue the outcome.

Keywords: evolutionarily stable strategy, iteroparity, Leslie matrix, population dynamics, reproductive schedule, semelparity.

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