Author's personal copy BIOLOGICAL CONSERVATION 141 (2008) 23– 34 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/biocon Environmental change hastens the demise of the critically endangered riverine rabbit (Bunolagus monticularis) Gregory O. Hughesa,d,*, Wilfried Thuillera,e, Guy F. Midgleya,c, Kai Collinsb aKirstenbosch Research Centre, South African National Biodiversity Institute, Private Bag X7, Claremont 7735, South Africa bMammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa cCenter for Applied Biodiversity Science, Conservation International, 1919 M Street, NW Suite 600, Washington DC 20036, USA dADAS UK Limited, Woodthorne, Wergs Road, Wolverhampton, WV6 8TQ, UK eLaboratoire d’Ecologie Alpine, UMR CNRS 5553, Universite´ J. Fourier, BP 53, 38041 Grenoble Cedex 9, France ARTICLE INFO ABSTRACT Article history: Declining population numbers coupled with the growing evidence of global change have Received 31 March 2005 focussed attention on the critically endangered riverine rabbit (Bunolagus monticularis) Received in revised form endemic to South Africa. The aim of this study is to develop a habitat model to aid in 14 August 2007 the identification of isolated populations, offer opportunities for re-introduction or intro- Accepted 14 August 2007 duction, and guide future conservation efforts by assessing the possible impacts of global Available online 7 November 2007 change. We attempt a novel approach where plant species which afford the riverine rabbit cover from predation and its primary food sources are modelled utilising the same tech- Keywords: nique and are included as a predictor variable in the habitat model for both current and Riverine rabbit future projections of potential habitat. Inclusion of this proximal variable as well as ripar- Habitat model ian areas yields a more parsimonious habitat model than using climatic variables alone. Global change Results suggest that unsurveyed suitable habitat east of Victoria West might harbour pre- Iand transformation viously overlooked isolated populations or offer new opportunities for re-introductions. Conservation Future climatic conditions under the most severe general circulation model for the region (HADCM3) suggest that, on average, in excess of 96% of the current habitat could become unsuitable, mitigated only slightly by a possible 7% increase in range in adjacent upper catchment areas. Consideration of existing land transformation increases this range reduc- tion by a further 1%. Given that ex situ captive breeding programmes have met with no suc- cess and that the bulk of future potential range lies well outside of the currently known and surveyed areas the current adaptation options of conservancy establishment and captive breeding need to be re-evaluated. Without positive human intervention the future of the critically endangered riverine rabbit under conditions of global change seems certain. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction breeding programmes (Dippenaar and Ferguson, 1994)have highlighted the urgent need for an evaluation of the in situ Rapidly declining numbers within known populations of the conservation of this South African endemic species. In situ critically endangered (Collins et al., 2003) riverine rabbit conservation, implies, inter alia, a detailed knowledge of the (Bunolagus monticularis) along with unsuccessful captive species’ current, potential and future range. In the case of * Corresponding author: Address: Kirstenbosch Research Centre, South African National Biodiversity Institute, Private Bag X7, Claremont 7735, South Africa. E-mail address: [email protected] (G.O. Hughes). 0006-3207/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2007.08.004 Author's personal copy 24 BIOLOGICAL CONSERVATION 141 (2008) 23– 34 the riverine rabbit this knowledge is incomplete with exhaus- 1903 (when the species was first described and was considered tive surveys of known and potential range underway yet to be wide spread) and the present, where the species is con- incomplete. While conservationists have acknowledged cli- sidered to be critically endangered (Collins et al., 2003) are mate and land-use change as a possible threat to Bunolagus attributed to a number of factors. Habitat transformation to monticularis (Ahlmann et al., 2000) these effects on remaining exploit the fertile alluvial floodplains adjacent to their riparian and future suitable habitat have not been explicitly analysed. habitat for winter wheat production heads this list, with in ex- Habitat-based models have been increasingly used as a cess of 60% of this riparian habitat having been transformed means to inform conservation (Engler et al., 2004; Lehmann (Ahlmann et al., 2000; Coetzee, 1994; Duthie, 1989; Duthie et al., 2002; Li et al., 1999; Wu and Smeins, 2000) especially and Robinson, 1990; Duthie et al., 1989). Habitat degradation in the light of continued environmental change (Arau´jo through fuel-wood collecting and overgrazing has lead to an et al., 2004; Aspinall and Matthews, 1994; Box et al., 1999; increase in predation, while the reduction in streamflow ow- Midgley et al., 2002). Of interest to this study is their ability ing to the construction of dams upstream, as well as hunting to aid in the identification of locations that might hold un- with dogs, have all played a role (Ahlmann et al., 2000). known populations (Guisan et al., 2006; Raxworthy et al., 2004), guide the introduction (Debeljak et al., 2001) or re-intro- 2.2. Distribution data duction of species (Glenz et al., 2001; Zimmermann and Bre- itenmoser, 2002) and restoration of habitats (Lehmann et al., Point distributions of known populations were compiled from 2002; Midgley et al., 2003) as well as assess the extent of future a number of surveys undertaken by conservation agencies habitat (Hilbert et al., 2004; Teixeira and Arntzen, 2002). and researchers as well as field observation. The presence re- This study aims to investigate some of the factors driving cords of a recently discovered Touws River population in the the distribution of the riverine rabbit, to delineate current Fynbos biome were excluded from this study for two reasons. suitable habitat in the hope of identifying unsurveyed areas Firstly, research to date has centred on the Karoo populations which may harbour isolated populations or offer opportuni- and observations for these may not be valid for this southerly ties for re-introduction or introduction of the species, and population e.g. food species observed for the central Karoo guide future conservation efforts by assessing the possible population do not occur in the Fynbos biome, and secondly, impacts of global change and adaptation options through genetic research suggests that this southerly population is in- the development and validation of a habitat model. deed distinct from the Karoo population (Mathee, C., Pers. Paleo-climatological research has highlighted that rapid Comm., 2005). changes in vegetation cover (over as little as 100 years) Owing to the modelling technique requiring absence data may have led to a change in faunal composition (Post, 2003). and in order not to bias the modelling with the effects of prev- The identification and inclusion of resource predictor vari- alence (Manel et al., 2001), an equal number of pseudo- ables, measured, modelled or inferred, in landscape scale absence sites were inferred using the following technique. A habitat models is not uncommon, with examples including grid of points was generated across the whole of South Africa soil hardness for burrow excavation (Calvete et al., 2004), tree in order to ensure that a complete response curve is gener- cavity availability (Lawler and Edwards, 2002), prey density ated as truncated response curves may lead to spurious (Glenz et al., 2001; Palomares et al., 2001) and potential fruit results on projection (Thuiller et al., 2004). The presence production (Pearce et al., 2001). While the dependence of spe- observations were used to create a convex polygon, which cies future ranges on vegetation under scenarios of climate by definition is the smallest convex set of points to include change have been postulated (Huntley, 1995) models of faunal all of the points. Grid points within this convex polygon were responses to climate change typically do not include the ef- excluded if they occurred within 1 km of ephemeral streams fects of proximal resource variables. In this study we attempt or occurred on terrain with a slope of less than 30%. A random a novel approach where plant species which afford the river- sub sample of the remaining grid points was chosen such that ine rabbit cover from predation and its primary food sources an equal number of absence points were selected from within are modelled utilising the same technique and are included and without the convex polygon. The final distribution used as a predictor variable in the habitat model for both current in the modelling is illustrated in Fig. 1. and future projections of potential habitat. 2.3. Ecological data 2. Materials and methods A thorough search of available literature along with field 2.1. Study species observations yielded the possible food sources on which the riverine rabbit relies as well as the plant species that it uses The riverine rabbit is a lagomorph endemic to the semi-arid for cover from predation. Field observations identified Salsola central Karoo region of the western and northern