The relevance of the Greater Cederberg Biodiversity Corridor (GCBC) for reptile conservation

[摘要] ENGLISH ABSTRACT: The Greater Cederberg Biodiversity Corridor (GCBC) is a large-scale conservationcorridor situated in the south-western region of South Africa. Delineation of the GCBCwas largely based on by vegetation data. The relevance of the GCBC for theconservation of the reptilian fauna in the area south of 31°S and west of 21°E is assessedin the present study. This entailed determining the GCBC's coverage of regional reptilediversity patterns and assessing its potential conservation significance during possibleclimate induced changes in reptile distributions.Reptile species point distribution data from the preliminary (2007) SARCA (South AfricanReptile Conservation Assessment) database was used. Under-representation of theTankwa Karoo in the dataset required a field survey of this region. Additionally, thebiogeographical influence of the arid Tankwa Karoo Basin on the distribution of reptiles inthe south-western districts of South Africa was investigated. Turnover across the Basin ishigh, species richness is lower than in surrounding mountainous areas and there are nospecies endemic to the area. The Tankwa Karoo Basin acts as a dispersal barrier formany reptile species occurring in the surrounding more mesic areas. At the same time,the ranges of a number of typical northern, arid adapted species extend southward alongthe Tankwa Plains. A number of species range extensions in the region are reported.Patterns of endemism, species richness and turnover were plotted from the pointdistribution data at quarter and eighth degree square resolution. Extensive sampling biastowards reserves and populated areas is apparent from the reptile species richness plots.This pattern is more pronounced for snakes than lizards. Reptile richness is particularlyhigh along the north-south section of the Cape Fold Mountains and also relatively highalong the south-western coast, peaking in the Lambert's Bay area. The majority of the 20reptile species endemic to the study area are associated with one of two identified centres of endemism: the Greater Cederberg area, or the narrow coastal zone stretching from theLambert's Bay area to the Cape Peninsula. An additional third set of endemics comprisedof melanistic forms restricted to a number of different refugia, notably, Landroskop, theCape Peninsula, Sladanha-Langebaan region, Piketberg Mountains and a confined areaalong the western section of the Cape Fold Mountains. Species richness and endemismpatterns co-vary within the study area.Biotic regions were identified through hierarchical clustering of grid cells according toshared species occurrences. A Northern, Southern, Central and Western biotic regionwas identified. Classification tree methodology (CART) and Canonical CorrespondenceAnalysis (CCA) were used to characterise defined biotic regions in terms of selectedenvironmental variables. Four sets of species assemblages are described on the basis ofthese biotic regions – two major and two minor ones. Of the major assemblages theNorthern assemblage can be described as an arid zone one and the Southernassemblage as a mesic zone one. The minor Central assemblage, comprising mainlyrock-dwelling forms, represent evolutionary leftovers as a result of climate change inducescycles of contraction and expansion of arid and mesic faunas. The other minor one, theWest Coast assemblage could be considered a sub-assemblage of the Northern one, withparticular adaptation to the coastal climate. Environmental characterisation of the bioticregions reveals that these groupings are supported by an environmental signal. Thecontiguity of four distinct sets of reptiles, each with its own set of environmentalrequirements, in this relatively small geographic area clearly indicates that the southwesternregion of South Africa is biogeographically complex.The GCBC incorporates the largely coinciding centres of endemism and richness alongthe West Coast and the greater Cederberg area. Although the centre of endemism formelanistic reptile forms, in the Saldanha-Langebaan area, falls just south of the GCBCboundary, the Corridor fulfils the requirements for effective conservation of reptiles in the area to a large degree. The north-south dispersal pathways provided by the Corridoralong the Cape Fold Mountains is believed to be adequate to buffer climate changeeffects, however there is concern about its ability to contribute to the persistence of theassemblage associated with the narrow coastal zone in the west.

[发布机构] Stellenbosch University