The spatial distribution of African savannah herbivores: species associations and habitat occupancy in a landscape context

Abstract

Herbivores play an important role in determining the structure and function of tropical savannahs. Here, we (i) outline a framework for how interactions among large mammalian herbivores, carnivores and environmental variation influence herbivore habitat occupancy in tropical savannahs. We then (ii) use a Bayesian hierarchical model to analyse camera trap data to quantify spatial patterns of habitat occupancy for lions and eight common ungulates of varying body size across an approximately 1100 km 2 landscape in the Serengeti ecosystem. Our results reveal strong positive associations among herbivores at the scale of the entire landscape. Lions were positively associated with migratory ungulates but negatively associated with residents. Herbivore habitat occupancy differed with body size and migratory strategy: large-bodied migrants, at less risk of predation and able to tolerate lower quality food, were associated with high NDVI, while smaller residents, constrained to higher quality forage, avoided these areas. Small herbivores were strongly associated with fires, likely due to the subsequent high-quality regrowth, while larger herbivores avoided burned areas. Body mass was strongly related to herbivore habitat use, with larger species more strongly associated with riverine and woodlands than smaller species. Large-bodied migrants displayed diffuse habitat occupancy, whereas smaller species demonstrated fine-scale occupancy reflecting use of smaller patches of high-quality habitat. Our results demonstrate the emergence of strong positive spatial associations among a diverse group of savannah herbivores, while highlighting species-specific habitat selection strongly determined by herbivore body size. This article is part of the themed issue 'Tropical grassy biomes: linking ecology, human use and conservation'.

Tropical grassy biomes: linking ecology, human use and conservation

“…Archibald & Hempson [16] explore trade-offs in fire and mammalian herbivory across the African continent where realms of influence can change through space and time. Complementing this research is that of Anderson et al [43], who examine spatial associations of African mammalian herbivores relative to body size and influences on ecosystem function relative to species composition. Both of these studies raise important questions about the function or dysfunction of TGBs in the context of changing disturbance regimes.…”

“…For the first time, analyses are presented on the biogeography and potential distributions of Asian savannahs [39]. Other significant steps forward in our understanding include: methods for characterizing ancient versus derived grassy biomes [40,41], comparative data on the species diversity of TGB regions across the globe [42], an improved understanding of the complex ecology of herbivory and fire [16,43] and the context-dependent response of vegetation to global change [44], and finally, tools to examine trade-offs in biodiversity, carbon and agriculture to aid land-use planning and policy [10].…”

“…The increasing extent of roads and fences act as fire breaks and also prohibit large-scale animal movements [6]. These changes to the major savannah processes of fire and herbivory, combined with the impacts and effects of the poaching crisis of Africa and Asia, are likely to have profound consequences for ecosystem function [16,43].…”

Natural and anthropogenic drivers of cub recruitment in a large carnivore

“…In the Maasai Mara, burning has been shown to increase both herbivore and carnivore abundance in areas postburn. However, burning can accelerate habitat conversion and increase habitat homogeneity, while attracting small ungulates (Anderson et al., 2016), the preferred prey species of female cheetahs with cubs (Broekhuis et al., 2018). Burning could therefore create an “ecological trap” by attracting female cheetahs to open areas where prey abundance is high, but cub recruitment is low (Schlaepfer, Runge, & Sherman, 2002).…”

The underestimated biodiversity of tropical grassy biomes

“…associated with open biomes-such as grasses, megaherbivores (both grazers and browsers), and the large carnivores that prey on them-their centres of diversity lie in regions dominated by non-forest, grassy biomes [33]. These systems represent some of the most iconic and spectacular examples of complex terrestrial foodwebs-such as the Serengeti in East Africa [34]-and will inevitably feature prominently in humanity's efforts to conserve the natural world. The recent availability of globally consistent maps of the species richness of key taxa has allowed significant advances in our understanding of the global distribution of biodiversity [5,35].…”