Stable isotope niche segregation between rare topi antelope (Damaliscus lunatus korrigum) and other sympatric bulk grazers in Pendjari Biosphere Reserve (Northern Benin): Implication for topi conservation

Abstract

Understanding factors limiting rare species is a major concern in conservation ecology. Little is known about how large mammalian bovid species from West Africa partition diet resources, and to what extent the rare topi antelope and other sympatric bulk grazers can cope with this co-existing system. Using tooth collagen stable isotope data, we studied an assemblage of three sympatric grazers (topi, hartebeest and roan) with different population density. Our findings showed numerous patterns in resource partitioning amongst the three sympatric species studied, suggesting that the species used dietary resources in contrasting ways. There were significant differences in both δ13C and δ15N signatures among topi, hartebeest and roan. A very narrow range could be noticed for the rare topi antelope (−6.05‰ to −7.63‰) for δ13C values and no significant differences at individual scale. The more abundant species such as hartebeest and roan were found to use a high proportion of the isotopic niche space of topi (more than 70%), while topi used only a narrow range of hartebeest and roan niche space (less than 10%). Our study provides the first evidence for the resource partitioning amongst high and low density ungulates in West African savanna. Expansion of the niche noted in the roan and hartebeest is much more related to the strong variation of the niche at the individual level. Topi, as subordinate species narrow their niche instead of expanding the dietary niche as expected. Our findings regarding the absence of dietary niche flexibility observed in the topi despite it being considered as subordinate species were discussed in being one of the factor limiting its population recovery in West African grazer assemblages.