The importance of grass cover for mammalian diversity and habitat associations in a bush encroached savanna

Abstract

In grasslands across the world, woody species are replacing grass cover. This bush encroachment can alter available food, cover, and space resources for most mammalian species; however, the specific responses of mammals to bush encroachment in African savannas remain largely unknown. We examined the fine-scale response of mammals across a gradient of bush encroachment using camera traps and a Bayesian hierarchical multi-species abundance model that estimates local relative abundance and species richness while accounting for imperfect detection. Additionally, we simulated species-specific relative abundances and species richness responses to differing bush encroachment management actions. Contrary to our expectations, the relative abundance of only one species showed a negative relationship to shrub cover and another to tree cover. However, the relative abundance of eight out of twenty-one species showed a positive association with grass cover. Mammal species richness increased with grass cover, decreased with shrub cover, and showed no clear pattern with increasing tree cover. Furthermore, our simulations suggest reducing and increasing shrub and grass cover respectively by 50% would increase species richness and local abundances for the mammal community of the area. Our results indicate grass cover exerts a strong influence on habitat use, relative abundances and species richness in bush encroached areas. Our study shows that mammal's positive response to grass cover is more important than potential negative impacts of increasing shrub cover. Consequently, recovering and maintaining adequate grass cover in savannas subject to bush encroachment is an indispensable condition to maximize mammalian diversity and abundances.