Megaherbivore response to droughts under different management regimes: lessons from a large African savanna

Abstract

Droughts are predicted to increase in frequency and intensity for large parts of Africa. It is unclear how this may impact native grazers in protected areas, and how these outcomes may differ under contrasting management approaches. Reducing artificial water sources and increasing the size of protected areas have been proposed as management responses that could possibly increase system resilience and buffer herbivores against large-scale mortality during droughts. Long-term spatially explicit buffalo, elephant and hippo census data from the Kruger National Park and adjacent private protected areas during three droughts (1982/1983, 1991/1992 and 2015/2016) provided a unique opportunity to explore how a range of management actions influenced megaherbivore responses across six regions. Drought responses varied significantly at a regional scale for all three megaherbivores, supporting the notion that size, and the associated emergent property of spatio-temporal heterogeneity, provides a buffer during droughts. Furthermore, regional buffalo population declines (as a function of mortality, movement and birth rates) were highest in areas with high waterhole density and concomitant low levels of herbaceous biomass, compared with areas that experienced similar rainfall, but had lower waterhole density and higher herbaceous biomass. Elephant mortalities were negligible, but elephants displayed regional movement patterns, seemingly attracted to higher water provision densities during the drought. Our results highlight that drought interacts with spatio-temporal environmental gradients and management actions and illustrates how the Greater Kruger National Park is increasingly functioning as an integrated ecosystem for megaherbivores.