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https://hdl.handle.net/20.500.12143/6813

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Browsing Conference presentations by Author "Alexander, Graham J."

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    South African reptile species and their phylogenetic richness not sufficiently safe-guarded
    (2019-09-09) Maritz, Bryan; Verburgt, Luke; Bates, Michael F.; Conradie, Werner; Hofmeyr, Margaretha D.; Turner, Andrew A.; Alexander, Graham J.
    African reptiles are under threat primarily due to habitat loss as a result of agriculture, resource extraction, and urbanisation. Extinction risk of South African reptiles was assessed as of 2018 using IUCN criteria and we ‘backcast’ these assessments to infer extinction risk circa 1990. A Red List Index (RLI: a measure of the extinction risk for a group of species) for 1990 and 2018 was estimated, and the protection level afforded to South African reptiles was investigated by intersecting reptile distributions with the network of protected areas. Furthermore, phylogenetic diversity of South African reptiles was mapped and intersected with national land cover for 1990 and 2013 to identify areas of high phylogenetic richness that may be impacted by habitat transformation. Level of extinction risk for South African reptiles (ca. 5.4%) is lower than the global average, and most currently threatened species would have already been at risk by 1990. The RLI is slightly lower in 2018 than it was in 1990, and the decrease is more prominent for endemic reptiles than for all reptiles combined. Most South African reptiles fall into the Well Protected category, implying that the protected area network has substantial conservation impact. However, most threatened reptile species are Poorly Protected or Not Protected. The current extent of the protected area network therefore, does not adequately mitigate extinction risk for reptiles. Notably, two South African reptiles are Critically Endangered and in protected areas, two others are already classified as Extinct, and rough estimates of extinction rates are similar to values estimated for other vertebrates. Phylogenetic diversity mapping showed that the greatest historical impacts to phylogenetic richness for reptiles are in the northeast (Limpopo, Mpumalanga, and Gauteng provinces), southwest (Western Cape Province) and the coastal margin of KwaZulu-Natal. By considering additional metrics that are directly guided by our in-depth knowledge of the species, their distributions and the threats, we demonstrate that South African reptiles are under pressure, that risk of extinction is tangible for several species and that phylogenetic richness of reptiles in certain areas of South Africa is imperilled by loss of habitat.
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    A zone of geographic overlap between two morphologically similar African skinks
    (2019-09-09) Makhubo, Buyisile G.; Alexander, Graham J.
    Trachylepis is a morphologically conservative, species rich genus of African skinks. Recent genetic analyses within Trachylepis have identified several cryptic lineages as distinct species; however, phenotypic conservatism makes it difficult to rely only on morphology for distinguishing species, especially in the field. In the T. striata group, there are a number of species that are commonly misidentified in the field, for example T. punctatissima and T. spilogaster. Previous phylogenetic work reveals clear genetic divergence between the two species, yet their morphological similarity makes them difficult to distinguish particularly where they are in sympatry, such as in the North West Province, South Africa. Thus, the area of sympatry may either be genuine or the result of misidentification. We examined these alternatives by sequencing individuals from the potential overlap zone and evaluated them within a phylogenetic framework. A preliminary phylogeny using one mitochondrial marker (16S) was constructed using the Bayesian and maximum likelihood methods. There is evidence of a narrow zone of geographic overlap between the two species, although the area of sympatry appears to be smaller than previously thought. Given that the phylogeny showed a number of misidentified individuals in the presumed area of sympatry, the current species distributions are probably overestimated as a result of historical misidentifications. Furthermore, the phylogeny showed that misidentification is a common problem throughout the entire T. striata group with a number of other species being misidentified. For T. punctatissima and T. spilogaster, sympatry exacerbates the likelihood of misidentification and should be considered when the species is studied in the North West Province. Additionally, genetic identification should be used to confirm morphological identification when working on the T. striata group because many samples were found to be incorrectly identified.