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

Abstract

Citation: Kihwele, E. S., V. Mchomvu, N. Owen-Smith, R. S. Hetem, M. C. Hutchinson, A. B. Potter, H. Olff, and M. P. Veldhuis. 2020. Quantifying water requirements of African ungulates through a combination of functional traits. Ecological Monographs 90(2):Abstract. 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.

Contrasting capabilities of two ungulate species to cope with extremes of aridity

“…Among the large ungulates inhabiting the Kalahari region, the arid-adapted gemsbok (or South African oryx; Oryx gazella gazella ) appears to possess a number of fixed functional traits allowing it to conserve body water and cope with the dry conditions 8 . For example, an increased relative medullary thickness may promote the production of concentrated urine, and a relatively large surface area to volume ratio of the spiral and distal colon may allow for more water to be absorbed, reducing moisture loss in dung 9 .…”

“…We further expected wildebeest to select cooler microclimates and spend a greater proportion of their time in these cooler shaded microclimates to reduce heat loads during the heat of the day, which may result in reduced daytime activity. 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.…”

Mapping and assessing the impact of small‐scale ephemeral water sources on wildlife in an African seasonal savannah

“…Our study considered impacts of ephemeral water only on buffalo and elephants. Previous research has shown that herbivores fall along a gradient of water dependence (Redfern et al 2003, Kihwele et al 2020). We would therefore hypothesize that browsers like kudu and giraffe, which are expected to be less water‐dependent than grazers (Redfern et al 2003), would show weaker relationships among ephemeral water and distribution/movements if subjected to similar analyses as performed here.…”

Functional traits of the world’s late Quaternary large-bodied avian and mammalian herbivores

“…We urge users to report errors or updates on newly published data for integration into HerbiTraits by filing an Issue on our GitHub ( https://github.com/MegaPast2Future/HerbiTraits ) repository page, or by emailing the corresponding authors. Furthermore, the GitHub ( https://github.com/MegaPast2Future/HerbiTraits ) page includes an incomplete trait file, which contains other ecologically relevant traits, such as adaptations for digging and free water dependence 60 . These traits remain unavailable for many taxa, but provide a starting point for further data collection and analysis.…”