Spatial ecology of male hippopotamus in a changing watershed

Keenan Stears,Benezeth M Mutayoba,Tristan A Nuñez,Epaphras A Muse,Douglas J Mccauley

doi:10.1038/s41598-019-51845-y

Abstract

The obligate dependency of the common hippopotamus, Hippopotamus amphibius, on water makes them particularly vulnerable to hydrological disturbances. Despite the threats facing this at-risk species, there is a lack of information regarding H. amphibius spatial ecology. We used high-resolution tracking data of male H. amphibius to assess home range size, movement mode (e.g. residency and migratory movements), and resource selection patterns. We compared these results across seasons to understand how hydrological variability influences H. amphibius movement. Our study watershed has been severely impacted by anthropogenic water abstraction causing the river to stop flowing for prolonged periods. We observed H. amphibius movements to be highly constrained to the river course with grassy floodplains being their preferred habitat. Dominant and small sub-adult males displayed year-round residency in/near river pools and had smaller home ranges compared to large sub-adults. During the dry season, large sub-adult males made significant (~15 km) upstream movements. The larger home range size of large sub-adults can be attributed to the elevated levels of migratory and exploratory activities to limit conspecific aggression as the river dries. Our observations provide insight into how future changes in water flow may influence male H. amphibius movements and populations through density-dependent effects.

Highlights

The obligate dependency of the common hippopotamus, Hippopotamus amphibius, on water makes them vulnerable to hydrological disturbances
Previous research on H. amphibius spatial ecology has been based upon directly observing H. amphibius as they move across landscapes and manually following H. amphibius foraging paths[42,43]
Our results provide a first view of how male H. amphibius use their environment

Summary

Introduction

The obligate dependency of the common hippopotamus, Hippopotamus amphibius, on water makes them vulnerable to hydrological disturbances. We used high-resolution tracking data of male H. amphibius to assess home range size, movement mode (e.g. residency and migratory movements), and resource selection patterns We compared these results across seasons to understand how hydrological variability influences H. amphibius movement. In African savannas, the common hippopotamus (Hippopotamus amphibius) is an important ecosystem engineer because it shapes the physical structure of ecosystems[1], vegetation communities[2,3], and biogeochemical cycling[4,5] These effects are detectable in both aquatic and terrestrial ecosystems. Seasonal drying events that reduce river flow can naturally limit the number of aquatic refugia (e.g. deep river pools) for H. amphibius and can cause large, densely packed aggregations of H. amphibius to form within remaining pools[5,11] This dry season crowding can become exacerbated under conditions where river discharge has been significantly reduced due to anthropogenic water abstraction. The mechanisms that drive H. amphibius movements can influence their fitness as well as regulate the aforementioned effects that H. amphibius have upon communities and ecosystems e.g.13,14

Objectives

Methods

Results

Discussion

Conclusion