The majority of animal species on Earth have a complex life cycle, characterised by distinct shifts in ecological niche during ontogeny. These ontogenetic niche shifts involve changes in resource use, habitat as well as susceptibility to predators. Ontogenetic niche shifts are especially common among species that grow over a substantial range of body size between birth and maturation. Recent theory has shown that an ontogenetic niche shift in consumers, which exploit different resources during their juvenile and adult stage, may lead to alternative stable equilibria in a consumer-2 resources system. The consequences of ontogenetic niche shifts for the dynamics of communities involving multiple trophic levels are, however, as of yet unknown.
I will discuss the effects of an ontogenetic shift in resource use by consumers on the possible equilibria of a community of 2 resources, one or two consumer and up to two predator species as predicted by stage-structured biomass models. Bistability between an equilibrium with and without predators may occur over a range of resource productivities for generalist predators that forages on both consumer stages to an equal extent. On the other hand, specialist predators that specialise on either juvenile or adult consumer individuals are predicted to go extinct when alone if the productivity of the resource for their main prey is increased. When together, however, persistence of the two predator species in stable equilibrium with the consumer is guaranteed over the entire range of resource productivities for which they can not survive on their own. Finally, we will show that ontogenetic niche shift may also have surprising consequences for competition between consumer species, in particular in the presence of shared predators.
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