Department of Geography and Environmental Sciences

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Browsing Department of Geography and Environmental Sciences by Author "Baxter, R. M."

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    Investigating past, present and future distributions of cryptic species of vlei rats (otomys auratus, o. irroratus s.s and o. angoniensis) in South Africa, with a focus on Limpopo Province
    (2015-02-26) Nengovhela, Aluwani; Taylor, P. J.; Baxter, R. M.
    How the living world will respond to changes in climate is still a pressing issue to biologists today. This study investigated past, present and potential future di.stribution of three cryptic species of Afromontane rodents (Otomys auratus, 0. angoniensis and 0. irroratus s.s); as well as geographical and temporal trends of two species (0. auratus and 0. angoniensis). Investigation of past distributions included two species only (0. auratus and 0. angoniensis) in the northern escarpment (Limpopo, Gauteng, North West and Mpumalanga Provinces); current and potential future distribution considered the South African range of all the three species (Otomys auratus, 0. angoniensis and 0. irroratus s.s). We assessed the potential impact of changes in future climate on 0. auratus, 0. angoniensis and 0. irroratus s.s using predictive niche modelling. Distributional data were obtained from: field trapping, owl pellets analysis and Museum records [Ditsong National Museum of Natural History (formerly Transvaal, TM) and Durban Natural Science Museum (DM)]. Maximum Entropy (Maxent) was used to model the current distrib�tion of all three species. A general circulation model was used to predict the distribution of these species in 2070. Each of the three species is associated with a particular Biome i.e. 0. irroratus s.s is associated mostly with Fynbos and Thicket Biomes, 0. auratus with Grassland Biome and 0. angoniensis with Savannah Biome and we predict that their distribution will follow those predicted for their respective Biomes. Niche models were found to follow biome boundaries of each species. This scenario predicted a south east shift (auratus), a south west shift (angoniensis) and a shrink (irroratus s.s) in future distribution, according to each species preferred habitat. A concomitant 66% (auratus) and 36% (irroratus s.s) reduction in areas of high environmental suitability of these species is shown, with a I % gain in angoniensis. High rainfall and low temperatures modulated the distribution of both auratus and irroratus s.s while angoniensis was high rainfall and high temperatures. And this was consistent with the ecological requirements of each species. No historical distribution changes were documented in Rietvlei Nature Reserve and at the Waterberg Mountain Range for angoniensis and auratus when tested in Chi-square tests but changes were observed at the Soutpansberg Mountain Range. This study found that both multivariate and univariate morphometric approaches support the fact that cranial size (and presumable therefore body size) in 0. auratus but not in 0. angoniensis, is showing some response to climate variables, even within the restricted northern South African region (former Transvaal). Skull size of O. auratus decreased significantly in relation to the year of collection and was also significantly and positively related to latitude, thus conforming to Bergmann's rule.
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    Potential impacts of climate change on myosorex as a model for extinction risk of montane small mammals in South Africa
    (2015-02-26) Owino, Lilian Ogony; Taylor, P. J.; Baxter, R. M.; Ogola, J. S.
    The work focussed on the potential impacts of climate change on Myosorex species endemic to South Africa. The study investigated the potential impacts of climatic variables (temperature and rainfall) on the distribution of M. cafer, M. varius, M. sc/ateri, M. longicaudatus, southern and northern lineages of M. varius, and Myosorex cf. tenuis from Limpopo Province in space and time. The study also investigated the Myosorex species occurring in Limpopo Province by using morphological analysis. Ecological niche modelling using Maxent was applied to predict current and future distribution of these species. Eight bioclimatic variables for current and future projected scenarios together with occurrence data from South African Museums, new field collections from Soutpansberg Mountains and published data were used to build the models. Equal sensitivity and specificity threshold was used to map suitable habitat and the number of resolution were counted to get the present and future range including percentage decrease or increase in range. The current distributions and the future distributions for all the species were compared to determine the range shifts. The model results for range shifts revealed that the more temperate species such as M. cafer, M. /ongicaudatus and M. varius will suffer high profound contractions while those from the subtropical or coastal lowland ranges (Myosorex cf. tenuis, and M. sclateri) will even increase the range of suitable conditions, but given their poor dispersal capability and the absence of suitable habitat such as forest in the new ranges, these increases may not be realised. The northern and southern lineages of M. varius will suffer minimal range contraction. M. longicaudatus showed greatest contraction of suitable habitats, consequently, will experience the highest risk of extinction, at least in some parts of its range as a result of global warming associated with climate change by the year 2070. The results showed that global warming is an important factor that results in range shifts, thus affecting the distribution of Myosorex species in South Africa. Morphological results indicate that the Myosorex occurring in Limpopo Province is a distinct species that may be called Myosorex cf. tenuis.
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