Stable isotopes uncover trophic ecology of the West African crocodile (Crocodylus suchus)

Abstract

Stable isotope analysis is a widespread tool in ecological studies of diet composition and habitat use. In deserts, freshwater environments constitute threatened local hotspots of biodiversity. In these environments, stable isotopes may help to describe trophic ecology of top-predators. We examined stable carbon (δ13C) and nitrogen (δ15N) isotopes from scute keratin samples of 33 Crocodylus suchus and muscle samples from 39 potential prey collected in Southern Mauritania. Isotope ratios were compared among crocodiles according to size (non-adult and adult), and habitat (rock pools and floodplains). There was a significant interaction effect of habitat and size on crocodile δ13C values. Whereas δ13C was similar for all crocodiles collected in rock pools, adults had lower signatures than non-adults in seasonal floodplains. δ15N indicated an ontogenetic dietary shift with adult crocodiles foraging on prey from higher trophic level. Standard ellipse areas showed wider isotopic niches for adult than non-adult crocodiles, and within adults, for those from floodplains than those from rock pools. These environments are small, seasonal, overexploited for livestock watering, and polluted. They support very small and isolated crocodile populations. This study is aimed to provide conservation authorities with baseline information to strictly protect water-bodies where these predators subsist in arid environments.