Assessing the likelihood that burrowing gerbils in the central Namib are ecological engineers

Abstract

Like many other fossorial rodents, gerbils are known to modulate their environments by changing the soil characteristics and conditions via their activities such as ground bioturbation, foraging, defecating and urinating. They play an important ecological engineering role because they can affect water hydraulic conductivity and water holding capacity, mineralization rates, thus plant-available-nutrients and moisture stored in the soil profile. If the bioturbation activities of gerbils affect water availability in the hyper arid environment, gerbils may create patches of favourable micro-sites for vegetation establishment and growth, and thus also affect the structure and function of the vegetation community at the landscape scale. The main objective of this study was to test whether the gerbil species are significantly improving the growth of vegetation through their burrowing activities on the Husab gravel plains in central Namib. In this way I wanted to verify whether they play a functional ecological engineering role in the ecosystem. Firstly, the study mapped out the spatial distribution and density of vegetation patches with and without burrows on the Husab gravel plains of the central Namib and then selected specific areas for in-depth experimental study. The focus was on the effects of gerbils’ burrowing activities by comparing soil nutrients and moisture, and vegetation characteristics between contrasting sites (active burrow patches, inactive burrow patches, no-burrow vegetation patches and their control sites) on the Husab gravel plains. This study revealed that: (1) the spatial distribution and density of vegetation patches with and without burrows is not uniform and that the gerbils mostly prefer the grassy plain over other habitats. (2) The spatial distribution of density of their burrow patches can be explained by soil substrates such as surface cover and hardness. (3) Gerbils through their burrowing activities increase the hydraulic conductivity and soil’s fertility-related variables together with the vegetation cover, abundance and biomass. Thus, it can be concluded that gerbils significantly improve primary productivity through changing the conditions and characteristics of the soil on their burrow patches and this may have a knock-on effect on other organisms at the landscape level. Thus, gerbils may be considered to be essential ecological engineers in the central Namib.