On the brink of extinction—Habitat selection of addax and dorcas gazelle across the Tin Toumma desert, Niger

Abstract

Aim: To assess the distribution and occurrence of addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location: Tin Toumma desert, Niger. Methods: Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of addax and dorcas gazelle. Results: Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions: Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.