Ontogenetic Niche Shifts and Evolutionary Branching in Size-Structured Populations

Claessen, D. & Dieckmann, U. ORCID: https://orcid.org/0000-0001-7089-0393 (2001). Ontogenetic Niche Shifts and Evolutionary Branching in Size-Structured Populations. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-01-056

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Abstract

There are numerous examples of size-structured populations where individuals sequentially exploit several niches in the course of their life history. Efficient exploitation of such ontogenetic niches generally requires specific morphological adaptations. In this article we study the evolutionary implications of the combination of an ontogenetic niche shift and environmental feedback. We present a mechanistic, size-structured model in which we assume that predators exploit one niche while they are small and a second niche when they are big. The niche shift is assumed to be irreversible and determined genetically. Environmental feedback arises from the impact that predation has on the density of the prey populations. Our results show that initially, the environmental feedback drives evolution towards a generalist strategy that exploit both niches equally. Subsequently, it depends on the size-scaling of the foraging rates on the two prey types whether the generalist is a continuously stable strategy or an evolutionary branching point. In the latter case, divergent selection results in a resource dimorphism, with two specialist subpopulations. We formulate the conditions for evolutionary branching in terms of parameters of the size-dependent functional response. We discuss our results in the context of observed resource polymorphisms and adaptive speciation in freshwater fish species.

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