Understanding the role of fragmentation in informing small mammal diversity and abundance in Rûens Renosterveld

Widegger, Abigail

Understanding the role of fragmentation in informing small mammal diversity and abundance in Rûens Renosterveld

Master Thesis

2022

Abstract

This thesis engages with the theory of habitat fragmentation through the lens of small mammals within a highly fragmented landscape in the Overberg, South Africa. The study explores habitat features in fragments of Eastern Rûens Shale Renosterveld associated with small mammal diversity and abundance and explores the potential processes driving ecosystem functioning in this region, with the aim of strengthening the knowledge underpinning our understanding of ecological patterns and processes in this critically endangered vegetation type. In the first part of this study, the effect of habitat fragmentation on small mammal communities was investigated by comparing species richness, diversity, and abundance between small, medium, and large fragments of renosterveld within an agricultural matrix. The study shows that medium and large fragments support greater small mammal richness, diversity, and abundance, than small fragments, whilst also harbouring rare, and specialist species. Rhabdomys pumilio was abundant across the study area, and was the only species found in small fragments, albeit at low densities. There was no strong correlation observed between the size of fragments and small mammal species diversity and abundance, with habitat amount across the landscape potentially being a stronger determinant of small mammal diversity. The results suggest that other landscape and local features, such as cover by rocky outcrops and canopy diversity may play a greater role in determining small mammal diversity indices than area of fragment size alone. The second part of the study investigates dietary information of small mammal species in the region through the analysis of stable isotope ratios of carbon ( 13C/12C) and nitrogen ( 14N/15N) in faecal samples. The results are used to compare dietary differences between and within these species as part of understanding the biology of these species and their response to habitat fragmentation. The results do not indicate a clear response in the dietary partitioning in these species, but instead show that the diets of these small mammals appear to be variable, with no clear signal of niche or trophic separation, potentially indicating that the fragmentation in this region has led to these small mammals subsisting on a diet different to what would be expected, with omnivores displaying lower δ 13C than herbivores, and no clear trophic separation based on δ 15N between herbivores, omnivores and insectivores. This work is important for renosterveld conservation, which seeks to implement cost effective and ecologically appropriate restoration methods, through providing much needed information on the status of these ecosystem engineers in fragments where efforts may be prioritised. In addition, it points to the need for a habitat improvement across the region, where fragments are found mainly on private agricultural land, highlighting the need for landowner engagement in any conservation effort.

Keywords

Environmental and Geographical Science

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