Rationale (Changed due to New Information)
The Bontebok is a subspecies endemic to the East Coast Renosterveld bioregion within the Cape Floristic Region (CFR) of the Western Cape. It is an important South African conservation success story where a subspecies has been brought back from the brink of extinction in the 1830s by farmers in the Bredasdorp area. Currently (2014), the population estimate within the natural distribution range is 515 mature individuals (using a 75% mature population structure) on formally protected areas (including the Denel Overberg Test Range managed as an ecological unit within De Hoop Nature Reserve). Due to a lack of natural habitat availability within the natural range, the provincial conservation management authority, CapeNature, allows benign introductions of subpopulations outside of the historical range, in areas geographically adjacent to the natural range and possessing broadly similar habitat. Reintroductions into two such formally protected areas have been in place for at least five years with successful reproduction and these have increased the mature population to 664 individuals. Bontebok also exist on ranch lands and other private properties within the natural and benign introduction range. However, there are known incidences of intensive management and/or hybridisation with Blesbok (D. pygargus phillipsi) within these subpopulations. Preliminary estimates of privately owned subpopulations nationally, suggest that only 33–39% of these subpopulations can be considered sufficiently wild to be included in this assessment. This adds between 118 and 1,272 individuals (by extrapolating this proportion to the private properties with the most or least abundant subpopulations respectively), which potentially increases the mature population size to between 752 and 1,618 individuals. However, the overall numbers of pure Bontebok within this population range and the intensity of management of these subpopulations are currently unknown.Although Bontebok numbers within the benign introduction and extra-limital ranges are increasing, the core population within the natural range has not increased since 2004 (770 individuals in formally protected areas in 2004 compared to 686 individuals in 2014). Protected area expansion possibilities are limited within the natural range, thereby limiting core population growth. Currently, the extent of occurrence within the natural range is estimated at 8,779 km² and the current observed area of occupancy is 602 km². Including all known Bontebok-containing areas within both the natural and benign introduction ranges yields 1,453 km² of observed occupancy. We infer a continuing loss of suitable habitat from ongoing agricultural and urban expansion within the CFR (within the Western Cape, 107 km² land was converted to agriculture per year between 2006 and 2011, 31% occurred within Critical Biodiversity Areas; and there has been an 8.6% increase, from 1,029 km² to 1,118 km², in urban expansion between 2000 and 2013).
Given that the estimated mature population size (within the natural and benign introduction areas) ranges from 514 to 1,618 individuals, that numbers of hybrid animals are unknown, and that no long-term data from the private sector exist to prove that the population has passed the threshold for Near Threatened for five years, we take a precautionary purview and list Bontebok as Vulnerable D1. Additionally, because the upper estimate of the potential area of occupancy (AOO) is 1,453 km² and that there is continuing loss of suitable habitat that limits population expansion within both the natural and benign introduction range, as well as that all subpopulations are fragmented by fencing with no metapopulation plan in place, Bontebok also qualifies for Vulnerable under criterion B.
The major threats to Bontebok are the uncertainty around the number of hybrids within the existing population, lack of habitat availability within its natural range (thus limiting population expansion), and the lack of a metapopulation plan to sustain genetic diversity. High incidences of hybridisation might render the majority of Bontebok subpopulations unfit for Red List inclusion and low genetic diversity may ultimately reduce the resilience of the subspecies. These threats should be counteracted through (1) the identification of all pure Bontebok subpopulations (and thus more accurate assessment of true population size), (2) the development and implementation of an active metapopulation management plan for the pure Bontebok subpopulations to simulate gene flow, prevent inbreeding and to sustain a flourishing and resilient population; and (2) exclusion of Blesbok from core areas supporting Bontebok inside its natural range. Conservationists should thus incentivise landowners to become Bontebok stewards to expand the conservation estate for this subspecies within the natural and benign introduction range. Bontebok are able to use a variety of habitats, the key features being grassy landscapes and the availability of water. For example, they readily utilise short grass areas and transformed landscapes. This tolerance and hence relative ease of management, together with their iconic status, facilitates stewardship prospects. This assessment should be revised when such data become available.