When specialists compete: Increased competition as a cost of resource polymorphism.

摘要

Resource polymorphisms---the occurrence within a single population of alternative morphs showing differential resource use---are spectacular examples of diversity within species. Here, we empirically evaluate a potential constraint to resource polymorphism in spadefoot toad tadpoles. We characterize the dietary differences between alternative carnivore and omnivore morphs and assess the potential ecological consequence of any such differences. We found that, as a group, the ancestral omnivore morph is a trophic generalist, whereas the derived carnivore morph is a trophic specialist. Furthermore, we show that these specialist carnivores experience greater intramorph competition for their distinctive resources than do the generalist omnivores. In contrast to the situation in omnivores, functional limitations associated with the evolution of trophic specialization may preclude carnivores from switching to alternative resources when the resource for which they are adapted is depleted. Generally, such costs of resource specialization may often constrain the evolution of resource polymorphism.