Feeding habits in a dimorphic metapopulation of the tiger salamander Ambystoma tigrinum nebulosum

Facultative paedomorphosis in salamanders refers to the presence of two ontogenetic pathways in natural populations – paedomorphosis, in which individuals retain gills at the adult stage, and metamorphosis, in which larvae metamorphose. The Mexican Cut Nature Preserve (Colorado, USA) is composed of numerous ponds which are inhabited by paedomorphic and metamorphic tiger salamanders. While paedomorphs usually stay in the same aquatic habitat all their life, metamorphs may leave water and colonize other ponds. The aim of this study was to determine the feeding habits of the two morphs from this metapopulation. To this end, adults were caught by dip-netting, stomach-flushed, measured and marked. Paedomorphs were only found in permanent waters. Metamorphs were present in all habitats, but particularly in the temporary ponds. Diet differed between ponds – reflecting their invertebrate composition – with a preponderance of either microcrustaceans, fairy shrimp or insect larvae. In ponds inhabited by the two morphs, paedomorphs consumed more prey items. Because dry mass and energy content varied between invertebrates, feeding on some of them, such as fairy shrimp in the temporary ponds where they are abundant, gave high energy intake to the predators. Because such resources are only available to the dispersive morph, metamorphs are at the advantage in being able to avoid competition with paedomorphs in permanent ponds and in using transient resources from the productive temporary waters.