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

M P Veldhuis,H Olff,E S Kihwele,J G C Hopcraft,J O Ogutu,J P G M Cromsigt,N Owen‐Smith,Richard Ostfeld

doi:10.1111/ele.13350

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.

Highlights

Predicting how climate change will affect ungulate communities is urgent (Speakman & Krol 2010; Fuller et al 2014; Shrestha et al 2014; Fuller et al 2016; Pigeon et al 2016) because increasing land temperatures, changing rainfall regimes (Niang et al 2014) and habitat fragmentation increase the risk of regional extinctions (Ripple et al 2015)
We propose to integrate these constraints for ungulates in grasslands and savannas through a limited set of key functional traits using the large herbivore assemblages in African savanna ecosystems as a generalisable example
Our new framework in addition predicts regional ungulate diversity to increase with landscape heterogeneity in distance to water by enabling water-dependent and water-independent species to coexist through spatial partitioning of food

Summary

Introduction

Predicting how climate change will affect ungulate communities is urgent (Speakman & Krol 2010; Fuller et al 2014; Shrestha et al 2014; Fuller et al 2016; Pigeon et al 2016) because increasing land temperatures, changing rainfall regimes (Niang et al 2014) and habitat fragmentation increase the risk of regional extinctions (Ripple et al 2015). Given the current rate of climate change, we need to understand if important interspecific differences in adaptations to drought and high temperatures can be explained by variation in body size, or whether other (independent) functional traits are required to predict species responses to landscape gradients and climate change scenarios. Body size is a key functional trait for understanding the food requirements and predation risk of savanna ungulates, and for understanding their thermoregulatory constraints.

Results

Conclusion