Ecological shifts during larval development in two West African savanna frogs

Abstract

Abstract:During their ontogeny many organisms exhibit size and/or stage-specific variability in a variety of features related to morphology and ecology, leading to a shift in the ecological niche between size- or stage groups. We analysed such ecological shifts between four larval stage groups in each of two syntopic species of frogs (a total of 5870 individuals) in two West African savanna ponds in Côte d'Ivoire. We hypothesized and confirmed differences between stage groups in ecological variables related to microhabitat and feeding niche. Stage groups differed up to 1‰ in δ15N and 1.5‰ in δ13C isotopic signatures, up to 10 cm in selected water depth, up to 6 m in distance to the pond's edge, and in the coverage of submerged vegetation (range = 10–50%). However, the hypothesis that tadpoles with generalized mouthparts (Kassina spp.) exhibit more pronounced ontogenetic shifts in food-web position than a specialized filter-feeding species (Phrynomantis microps), and that differences between larval stages are more pronounced in a heterogeneous habitat (offering more choices of habitat and food niches) than in a homogeneous habitat (offering less choices) was only partly confirmed. This study underlines that potential niche shift during different ontogenetic stages is an important factor to be considered in ecological studies.