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Abstract
The ability to move is essential for animals to find mates, escape predation, and meet energy and water demands. This is especially important across grazing systems where vegetation productivity can vary drastically between seasons or years. With grasslands undergoing significant changes due to climate change and anthropogenic development, there is an urgent need to determine the relative impacts of these pressures on the movement capacity of native herbivores. To measure these impacts, we fitted 36 white-bearded wildebeest (Connochaetes taurinus) with GPS collars across three study areas in southern Kenya (Amboseli Basin, Athi-Kaputiei Plains, and Mara) to test the relationship between movement (e.g., directional persistence, speed, home range crossing time) and gradients of vegetation productivity (i.e., NDVI) and anthropogenic disturbance. As expected, wildebeest moved the most (21.0 km day–1; CI: 18.7–23.3) across areas where movement was facilitated by low human footprint and necessitated by low vegetation productivity (Amboseli Basin). However, in areas with moderate vegetation productivity (Athi-Kaputiei Plains), wildebeest moved the least (13.3 km day–1; CI: 11.0–15.5). This deviation from expectations was largely explained by impediments to movement associated with a large human footprint. Notably, the movements of wildebeest in this area were also less directed than the other study populations, suggesting that anthropogenic disturbance (i.e., roads, fences, and the expansion of settlements) impacts the ability of wildebeest to move and access available resources. In areas with high vegetation productivity and moderate human footprint (Mara), we observed intermediate levels of daily movement (14.2 km day–1; CI: 12.3–16.1). Wildebeest across each of the study systems used grassland habitats outside of protected areas extensively, highlighting the importance of unprotected landscapes for conserving mobile species. These results provide unique insights into the interactive effects of climate and anthropogenic development on the movements of a dominant herbivore in East Africa and present a cautionary tale for the development of grazing ecosystems elsewhere.
Highlights
Seasonal patterns of vegetative greenness were similar across each study area, with the Athi-Kaputiei Plains exhibiting the greatest range in landscape seasonality and the Amboseli Basin the least (Figure 2A)
By linking the movements of wildebeest across three study areas with contrasting dynamics of landscape productivity and anthropogenic disturbance, we found that high levels of human activity drove unexpected relationships between the movement capacity of herbivores and productivity of the landscape
We found movements to be most restricted at moderate levels of vegetation productivity (Athi-Kaputiei Plains)
Summary
The ability to move and exploit resources at multiple spatiotemporal scales is key to maintaining biologically viable wildlife populations (Bolger et al, 2008; Holdo et al, 2011). In a global synthesis of tracking data from 57 mammal species, Tucker et al (2018) found that mammals residing in areas with high levels of anthropogenic modification exhibited movements that were one-half to onethird the extent of their movements in areas with lower modification. Such contractions in movement are expected to have important implications for the maintenance of key biological processes (e.g., predator-prey interactions, nutrient cycling, disease transmission) and have been directly linked to population declines in a number of species (Boone et al, 2005; Boone, 2007; Blackburn et al, 2011; Herbener et al, 2012; Kauffman et al, 2021)
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