Responses and feedbacks of burrowing mammals under differently managed rangelands

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 potentially 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. In the Kalahari Desert ecosystem of Namibia's Omaheke Region this study compared the abundance and diversity of burrowing medium-sized nocturnal mammals between neighbouring livestock and wildlife land use types. 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 and non-growing seasons of 2016 to quantify differences in medium-sized mammal population dynamics. Using high resolution multispectral unmanned aerial vehicle imagery, burrow size and abundance as well as vegetation productivity was estimated. The study found a higher diversity of nocturnal medium-sized mammals on the wildlife reserve. Furthermore, clear seasonal patterns were observed. Whereas total sighting number was similar in the growing season and winter on the wildlife reserve; on the livestock farm, there were significantly more mammals spotted in summer, and far fewer in winter. Notably, we revealed that some species of mammal have clear habitat preferences during the different seasons. Results showed that shrub encroachment had a negative relationship with burrow number on both sites, with the livestock farm particularly susceptible. Importantly some benefits were indicated by areas around larger burrows showing higher vegetative productivity. Overall, the study provided valuable insights into the movements, strategies and potential benefits of these mammals. Further research is needed to determine the precise mechanisms by which the burrowers may provide ecosystem functioning benefits to the land users.