Nocturnal Medium-Sized Bioturbators And Their Ecosystem Services In Differently Managed Rangelands In The Kalahari And Pro-Namib

Abstract

Bioturbating organisms are known for their benefits to landscapes and ecosystems. Studies have to date largely focussed on invertebrates with very little known about the role burrowing mammals play, especially nocturnally active species. They are thought to be vulnerable to land degradation - such as shrub encroachment and livestock overgrazing - leading to increased negative effects on land productivity through the loss of their associated ecosystem services. The abundance and diversity of burrowing medium-sized nocturnal mammals between neighbouring livestock and wildlife land use types were compared in this study in three biomes in Namibia: north Kalahari, south Kalahari, and the Pro-Namib Desert. It postulated that bioturbation by nocturnal mammals is an important feedback mechanism leading to improved soil conditions and therefore improved vegetation productivity. The study used nocturnal road strip counts during the growing (summer) and dry (winter) seasons of 2016, 2017 and 2018 to quantify differences in medium-sized mammal population dynamics. High resolution multispectral unmanned aerial vehicle imagery was used to determine macropore abundance on the northern Kalahari sites, as well as vegetation productivity was estimated for the three study areas and years using Sentinel-2 satellite images. Rangeland productivity was investigated in the field by measuring grass biomass and moisture infiltration around burrow clusters and control sites with no burrows. On the ground burrow dimension and temperature measurements were collected to investigate the ecosystem services from bioturbation. The study found higher diversity and abundances of nocturnal medium-sized mammals and their burrows on the Kalahari wildlife reserves. Furthermore, clear seasonal patterns were observed. The Kalahari sites had more sightings during the dry season, whereas the Pro-Namib had more during the growing season. Aardwolf (Proteles cristata) and springhare (Pedetes capensis) were mostly recorded on the wildlife reserves and during the dry season, while bat-eared fox (Otocyon megalotis) were mostly recorded during the growing season. Scrub hare (Lepus saxatilis) showed no difference between seasons and land uses, although it was the species most sighted on the Pro-Namib livestock farm. Springhare were the most prolific species recorded in the Kalahari. Importantly, benefits were indicated by areas around burrow clusters showing higher vegetative productivity (more grass and higher soil moisture). This study has revealed and supported evidence that these under-studied mammals play an important role in ecosystem functioning and environmental integrity, which leads to more stable and resilient ecosystems. Further research is needed in Namibia in general, but particularly in the Pro-Namib on bioturbators and their activities.

Keywords: bioturbation, ecosystem engineer, ecosystem services, nocturnal mammals, rangeland productivity, Namibia.