Is the Intrasexual Competition in Male Red Deer Reflected in the Ratio of Stable Isotopes of Carbon and Nitrogen in Faeces?

Isotopic analysis of carbon and nitrogen in faeces is a reliable methodology for studying ecology in wildlife. Here, we tested this technique to detect variations in carbon and nitrogen isotopic ratios (δ 13 C and δ 15 N) in two different intrasexual competition scenarios of male Iberian red deer ( Cervus elaphus hispanicus ) using faeces of individuals collected during hunting actions in South-eastern Spain. The carbon isotopic ratio (δ 13 C) was not found to be significant, likely due to similar diet composition in all individuals. However, the nitrogen isotopic ratio (δ 15 N) was found to be lower in populations where sexual competition between males during the rut was higher compared to low-competition populations. Therefore, this study suggests a different use of proteins by an individual male red deer depending on the sexually competitive context in which he lives. Although further research is needed, these results show the potential of isotopic analysis as a tool for studying individual and populational variations in the level of intrasexual competition, with implications in evolutionary ecology and population management.