Quantifying water requirements of African ungulates through a combination of functional traits

Climate and land use change modify surface water availability in African savannas. Surface water is a key resource for both wildlife and livestock and its spatial and temporal distribution is important for understanding the composition of large herbivore assemblages in savannas. Yet, the extent to which ungulate species differ in their water requirements remains poorly quantified. Here, we infer the water requirements of 48 African ungulates by combining six different functional traits related to physiological adaptations to reduce water loss, namely minimum dung moisture, relative dung pellet size, relative surface area of the distal colon, urine osmolality, relative medullary thickness, and evaporation rate. In addition, we investigated how these differences in water requirements relate to differences in dietary water intake. We observed strong correlations between traits related to water loss through dung, urine and evaporation, suggesting that ungulates minimize water loss through multiple pathways simultaneously, which suggests that each trait can thus be used independently to predict water requirements. Furthermore, we found that browsers and grazers had similar water requirements, but browsers are expected to be less dependent on surface water because they acquire more water through their diet. We conclude that these key functional traits are a useful way to determine differences in water requirements and an important tool for predicting changes in herbivore community assembly resulting from changes in surface water availability. Variability in temperature and rainfall patterns is increasing, with consequent effects on resource availability for herbivores across Africa. For arid and semiarid regions throughout Africa, a reduction in the amount of precipitation received during the dry season is expected, which will likely trigger more recurrent and severe droughts (Engelbrecht et al. 2015, Bartzke et al. 2018). Droughts will not only influence herbivores indirectly through changes in food availability, but also directly through decreased surface water availability (Gaylard et al. 2003). Most ungulates in drylands and savanna ecosystems require access to surface water to maintain body fluid homeostasis. However, we lack a general understanding of how ungulate species differ in their water requirements and whether and how changes in surface water availability will affect the community composition of savanna ungulates. During the dry season, water‐dependent herbivores are constrained by their minimum fundamental frequency of drinking (Cain et al.