Large herbivore assemblages in a changing climate: incorporating water dependence and thermoregulation

Abstract

The coexistence of different species of large herbivores (ungulates) in grasslands and savannas has fascinated ecologists for decades. However, changes in climate, land‐use and trophic structure of ecosystems increasingly jeopardise the persistence of such diverse assemblages. Body size has been used successfully to explain ungulate niche differentiation with regard to food requirements and predation sensitivity. But this single trait axis insufficiently captures interspecific differences in water requirements and thermoregulatory capacity and thus sensitivity to climate change. Here, we develop a two‐dimensional trait space of body size and minimum dung moisture content that characterises the combined food and water requirements of large herbivores. From this, we predict that increased spatial homogeneity in water availability in drylands reduces the number of ungulate species that will coexist. But we also predict that extreme droughts will cause the larger, water‐dependent grazers as wildebeest, zebra and buffalo–dominant species in savanna ecosystems – to be replaced by smaller, less water‐dependent species. Subsequently, we explore how other constraints such as predation risk and thermoregulation are connected to this two‐dimensional framework. Our novel framework integrates multiple simultaneous stressors for herbivores and yields an extensive set of testable hypotheses about the expected changes in large herbivore community composition following climate change.

Long‐term persistence of wildlife populations in a pastoral area

“…Our multi‐species and long‐term monitoring data suggest that most species aggregate in MR during the dry season (Appendix ). Especially the few man‐made dams probably enable the dry season usage of MR by water‐dependent wildlife species such as zebra, wildebeest, and waterbuck (Veldhuis, Kihwele, et al, 2019). However, during the dry season, surface water is heterogeneously distributed in the ranch (Beattie et al, 2020), which may facilitate the coexistence of both water‐dependent and less‐water‐dependent wildlife as well as livestock species in MR (Veldhuis, Kihwele, et al, 2019).…”

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 . Strong selective pressures likely facilitated these specialized adaptations, such that gemsbok have shown little change in abundance in response to past drought conditions 10 .…”

Mapping Shade Availability and Use in Zoo Environments: A Tool for Evaluating Thermal Comfort

“…It is possible these differences may reflect the difference in body size between the male and females, as the male was nearly twice the weight of the females. Given the allometric scaling of body size in surface area-to-volume, larger individuals may be more susceptible to heat stress through increased heat production and reduced evaporation [9,[45][46][47][48]. In a study on takin behavior in a managed environment, Powell et al noted that male takin were observed to rest more in summer than female takin, suggesting larger male takin may face a greater thermal load and potentially increased risk of heat stress compared to smaller female takin [49].…”

“…Previous studies have documented a range of environmental variables that can impact welfare, including noise, lighting, and human presence (e.g., [1][2][3][4][5][6][7]). The thermal environment is likely to play a key role in the behavior and welfare of individuals as well, particularly for megafauna that are commonly housed outdoors, given the metabolic consequences of a large body size and allometric scaling of surface area to volume [8,9]. With projected increases of global temperatures resulting from climate change, understanding the impact of the thermal environment on animals is now more important than ever [10].…”