Abstract
AbstractSavanna ecosystems are vital for both economic and biodiversity values. In savannas worldwide, management decisions are based on the concept that wildlife and livestock compete for grassland resources[1-4], yet there are virtually no experimental data to support this assumption[1]. Specifically, the critical assessment of whether or not wild ungulates alter livestock performance (e.g., weight gain, reproduction or survival) has rarely been carried out, although diminished performance is an essential prerequisite for inferring competition[1]. Here we use a large-scale experiment in a semi-arid savanna in Kenya to show that wild ungulates do depress cattle performance (weight gain) during the dry season, indicating a competitive effect, but enhance cattle performance during the wet season, signifying facilitation. This is the first experimental demonstration of either competitive or facilitative effects of an assemblage of native ungulates on domestic livestock in a savanna ecosystem, and a unique demonstration of a rainfall-dependent shift in competition-facilitation balance within any herbivore guild. These results are critical for better understanding and management of wildlife-livestock coexistence in savanna ecosystems globally, and especially in the African savanna biome which crucially hosts the last remnants of an intact large herbivore fauna.
Highlights
Savanna ecosystems are vital for both economic and biodiversity values
We compared cattle weight gain, organic matter intake (OMI), diet selection, dietary digestible organic matter (DOM), crude protein (CP) and DOM/CP ratio, and herbage cover in treatment plots accessed exclusively by cattle and those they shared with medium-sized wild herbivores with or without megaherbivores
Competition is associated with depressed food intake by cattle in the shared treatments (Table 1), which corresponds with reductions in cover and selection by cattle of Pennisetum stramineum (Figs 2a-c), suggesting that this grass is a major source of competition between wild ungulates and cattle
Summary
We hypothesised that if native ungulates compete with cattle, cattle should experience decreased weight gain associated with decreased forage availability and quality, reduced selection of major herbage species, depressed food intake and reduced diet quality, when they share foraging areas with wildlife We predicted that these effects should be greater during the dry season when food is less abundant. In contrast to the net competition between wildlife and cattle demonstrated in the dry season, net facilitation was demonstrated during the wet season, overcoming what appear to be ongoing competitive effects This net facilitation was associated with differences in forage quality, including improved crude protein (CP) content and reduced DOM/CP ratio of cattle diet in plots shared with wild herbivores (Table 1). It would be worth exploring whether the seasonal competition/facilitation shifts we demonstrate here are paralleled along spatial gradients in rainfall and primary productivity
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