A Spatiotemporal Assessment of Dietary Partitioning between Color Morphs of a Terrestrial Salamander

When color pattern variation is co-adapted with other biological features, distinct color morphs may be separated along divergent niche axes, and data on niche partitioning can provide insight into how distinct color morphs are maintained over spatiotemporal scales. The Eastern Red-backed Salamander, Plethodon cinereus, contains two common color morphs (striped and unstriped) that differ along several trait axes in addition to coloration. Previous studies from a single population have suggested that dietary composition represents an important axis of ecological differentiation between morphs of P. cinereus. To determine if morphs partition prey resources over space and time, we collected stomach contents from morphs across six populations that ranged in color morph frequency from 100% striped to >99% unstriped, and sampled each population in a spring and a fall season. From each population and season, we also sampled leaf litter invertebrates to quantify morph differences in prey selection. Based on previous studies, we predicted striped morph diet would consist of higher quality prey in polymorphic populations, whereas in monomorphic populations, we predicted both morphs would have a more variable diet due to ecological release from intermorph competition. In the two polymorphic populations we examined, one showed no evidence of diet differences and the other mirrored differences reported from previous studies. There was no change in dietary breadth between polymorphic and monomorphic populations, and thus no signature of dietary release. Our results show there is a high degree of overlap between dietary and leaf litter invertebrates, suggesting both morphs of P. cinereus are generalist predators. Finally, we found dietary composition varied across seasons and populations, which demonstrates the importance of examining morph traits over spatial and temporal scales.