Recognition and management of ecological refugees: A case study of the Cape mountain zebra

Anthropogenic activities have led to long-term range contraction in many species, creating isolated populations in ecologically marginal and suboptimal habitats. ‘Refugee’ species have a current distribution completely restricted to suboptimal habitat. However, it is likely that many species are partial refugees, where one or more populations are managed in ecologically unsuitable habitat. Here, we develop a framework to assess potential refugee populations in marginal habitats using a model species: the Cape mountain zebra. We assessed habitat quality by the abundance and palatability of grass and diet quality using proximate nutrient and element analysis. High grass abundance was associated with higher population growth rates and zebra density and less skewed adult sex ratios. Furthermore, faecal nutrient and dietary element quality was also positively associated with grass abundance. Our results show that poorly performing populations were characterised by suboptimal habitat, supporting the hypothesis that the Cape mountain zebra has refugee populations. In addition, we found more variance in sex ratio and population growth rates in smaller populations suggesting they may be more at risk for random stochastic effects, such as a biased sex ratio, compounding poor performance. We show how the ‘refugee’ concept can be applied more generally when managing species with fragmented populations occurring across marginal habitats. More broadly, the results presented herein highlight the importance of recognizing the range of habitats historically occupied by a species when assessing ecological suitability. Identifying and mitigating against refugee, relict and gap populations is especially critical in the face of on-going environmental change.