Abstract
Southern Africa is expected to experience increased frequency and intensity of droughts through climate change, which will adversely affect mammalian herbivores. Using bio-loggers, we tested the expectation that wildebeest (Connochaetes taurinus), a grazer with high water-dependence, would be more sensitive to drought conditions than the arid-adapted gemsbok (Oryx gazella gazella). The study, conducted in the Kalahari, encompassed two hot-dry seasons with similar ambient temperatures but differing rainfall patterns during the preceding wet season. In the drier year both ungulates selected similar cooler microclimates, but wildebeest travelled larger distances than gemsbok, presumably in search of water. Body temperatures in both species reached lower daily minimums and higher daily maximums in the drier season but daily fluctuations were wider in wildebeest than in gemsbok. Lower daily minimum body temperatures displayed by wildebeest suggest that wildebeest were under greater nutritional stress than gemsbok. Moving large distances when water is scarce may have compromised the energy balance of the water dependent wildebeest, a trade-off likely to be exacerbated with future climate change.
Highlights
Favour the selection of highly efficient muscles to facilitate seasonal migration between regions with adequate forage and water[11], thereby increasing behavioural flexibility
With fewer fixed functional traits to conserve body water[8], we expected that wildebeest would spend more time travelling to diminishing surface water, thereby increasing total 24 h activity compared to gemsbok, especially during a drought season compared to a non-drought hot and dry season
The inclusion of species within the model did not significantly improve the model’s performance and was uninformative[27]. Both species doubled their cumulative cool microclimate use during the drought compared to the non-drought hot-dry season (Table 2, Fig. 2e)
Summary
Favour the selection of highly efficient muscles to facilitate seasonal migration between regions with adequate forage and water[11], thereby increasing behavioural flexibility. Despite these physiological and behavioural differences, our previous work showed that both wildebeest and gemsbok displayed similar body temperature profiles in a typical year[7]. With fewer fixed functional traits to conserve body water[8], we expected that wildebeest would spend more time travelling to diminishing surface water, thereby increasing total 24 h activity compared to gemsbok, especially during a drought season compared to a non-drought hot and dry season
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