Ontogenetic Dietary Shifts and Food Resource Partitioning in a Stream-Dwelling Urodela Community: Mechanisms to Allow Coexistence Across Seasons

Abstract

Trophic interactions are important factors structuring animal communities. Although food resource partitioning among salamanders living in syntopy has often been explored in freshwater systems, the potential influence of ontogenetic shifts and seasonal patterns on resource partitioning is little known. The aim of this study was to explore the seasonal patterns in food resource partitioning among developmental stages of two Urodela species ( Calotriton asper and Salamandra salamandra ) in a fishless stream. We tested the hypothesis that seasonal patterns in intra- and interspecific food resource partitioning may occur at two different levels: (i) diet composition and (ii) prey size. For the purpose of this study, food resource partitioning was approached at three scales: (i) ontogenetic (larva, immature and adult), (ii) seasonal (winter, spring, summer and autumn) and (iii) species. Inter- and intraspecific competition for food was measured as dietary overlap according to Schoener’s index. The overlap in diet among developmental stages and species was high. However, prey size and the contribution of terrestrial invertebrates to the diets changed among developmental stages of species. This suggests that competition for food may be alleviated by ontogenetic dietary shifts in prey size and terrestrial invertebrates use.