This study details results of small mammal surveys at 24 sites in four biomes (Nama- and Succulent Karoo, Albany Thicket, Grassland) as part of the Karoo BioGaps project to augment baseline biodiversity information needed to guide proposed fracking activities in the Shale Gas Development Area (SGDA) (Holness et al. 2016). A strategic Environmental Assessment (SEA), commissioned by the South African Government, evaluated the potential to exploit the supposedly substantial reserves of shale gas using hydraulic fracturing (“fracking”) in the Great Karoo Basin of South Africa. Terrestrial micromammals (<500g) were captured using Sherman livetraps (September 2016 to March 2017). Sampling over 6580 trap-nights produced 339 captures of 271 individuals representing 14 taxa. Trapping success was low 5.14% (mean per site 0.37± 0.61%). Most captures (87%) and individuals (83%) were recorded in the Nama-Karoo (294 captures, 226 individuals, 15 sites), whereas only 5 captures were recorded in Albany Thicket (3 sites). Four xerophilous/generalist species (Micaelamys spp. (Rock rats), Gerbilluscus paeba (Hairyfooted Gerbil), Macroscelides proboscideus (Round-eared Sengi), and Elephantulus spp. were numerically dominant at most sites, and within most biomes/bioregions; while five rare species were only ever recorded once. Mean α diversity (observed species richness Sobs) per site (2.88 ±1.99) and Shannon-Wiener diversity (1.70 overall, 1.04 ±0.33 per site) were low, with only 5.47 effective species (mean = 3.04 ±1.08 per site) and low equitability (0.64 overall). Sobs was highest in Nama-Karoo (13 species), and lowest in the Grassland and Albany Thicket biomes (2-5 species). Species accumulation/rarefaction curves did not reach asymptotes, and Sobs values for most sites/biomes/bioregions were significantly lower than Chao1 predicted species richness, suggesting that sampling effort did not accurately estimate species richness. However, trapping efficiency was generally high (56-100%; mean 86.7%) which compares favourably with that of two recent published studies in South Africa. Multiplicative beta diversity (βMt) across the SGDA was 4.56 indicating high species turnover between sites/biomes/bioregions. Species turnover was high across biome boundaries, notably Albany Thicket-Grassland (15), Nama-Karoo-Albany Thicket (14), and Succulent Karoo-Grassland (12). Biomes and bioregions tended to plot apart in ordination analyses with relatively low (40-60%) Sorenson similarity, indicating that most regional small mammal communities were well-differentiated. Despite data limitations, 66 new distribution records for 21 sites are reported for the SGDA. Total species richness (including historical records) was highest in the Nama-Karoo (19), particularly the Upper Karoo bioregion (19, mean 6.45 ±2.16, 11 sites), followed by the Grassland (16), and Albany Thicket (5) biomes. Total species richness records for most sites/regions fell within the iChao2 CI bounds, thus integrating trapping and historical records provided a relatively robust data set for subsequent spatial diversity analyses. However, even the total species richness dataset is likely to underestimate true diversity owing to not sampling arboreal species or detecting some cryptic species. Generalized linear analyses indicated that small mammal diversity indices were significantly associated with certain environmental/climatic parameters (livestock, drought). Despite the west to east increase in precipitation, highest diversity was concentrated in the arid north-west Nama-Karoo where dwarf shrubs and succulents predominate. This suggests that environmental and niche filtering are significant proximate factors shaping small mammal assemblages. No significant effects of biotic interactions (particularly competition following Diamond's (1975) first two rules) or resource-mediated niche limitations were evident for SGDA species assemblages. However, results for the Nama-Karoo (i.e. for a natural phytogeographical rather than geoeconomically-defined area) were significant suggesting that biotic interactions may also be proximate factors shaping local assemblages. Site assemblages were significantly nested, indicating that species at species-poor sites were subsets of those at richer sites; and thus, that site communities may have been structured by either long-term (ultimate) regional biogeographic processes (e.g. immigration and extinction related to distances between sites) or habitat filtering operating at local scales. Data deficiencies notwithstanding, my results present the most comprehensive landscape-level analysis for small mammals, and the only baseline dataset (based on randomized sampling) for the Greater Karoo and SGDA. While my results must be treated with caution, I am confident that the recommendations I make on species, sites and regions potentially vulnerable will be a useful guide to possible impacts of fracking in the study area.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/33212 |
| Date | 01 April 2021 |
| Creators | Nadine, Aboul-Hassan |
| Contributors | Bronner, Gary, O'riain, Justin |
| Publisher | Faculty of Science, Department of Biological Sciences |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MSc |
| Format | application/pdf |
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