Damaliscus pygargus ssp. pygargus
|Scientific Name:||Damaliscus pygargus ssp. pygargus (Pallas, 1767)|
Damaliscus dorcas ssp. dorcas Pallas, 1766
|Taxonomic Notes:||Appeared in the 1996 IUCN Red List as Damaliscus dorcas dorcas, but it is generally agreed that D. pygargus pygargus is the correct name (see Grubb in Wilson and Reeder 1993).|
|Red List Category & Criteria:||Vulnerable B1ab(ii,iii)+2ab(ii,iii); D1 ver 3.1|
|Assessor(s):||Radloff, F., Birss, C., Cowell, C., Peinke, D., Dalton, D. & Kotze, A.|
|Reviewer(s):||Kerley, G., Child, M.F. & Mallon, D.|
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.
|Previously published Red List assessments:|
|Range Description:||Bontebok are endemic to the Western Cape, South Africa, although introductions have been made in most provinces. Historically, they were confined to the coastal plain (60–200 m) east of the Kogelberg in the Western Cape where they are believed to have concentrated on the renosterveld areas (Boshoff and Kerley 2001, Skead 2011). Early settlers may have confused Bontebok and Blesbok (D. pygargus phillipsi), which overestimated the historical distribution of Bontebok. In reality the subspecies were separated by at least 320 km at the time of European settlement (Skinner and Chimimba 2005, Boshoff et al. 2015). Here, overhunting reduced it from locally abundant to the verge of extinction. It was saved from extinction in the mid-19th century by a few Cape farming families who protected the small remnant subpopulations. From a low of 22 animals in the original Bontebok National Park (established near Bredasdorp in 1931), the Bontebok population has gradually recovered (Van Rensburg 1975). Translocated Bontebok from Bontebok National Park have formed the nucleus of reintroduced populations in other protected areas such as provincial and local authority nature reserves. The Bontebok National Park subpopulation is genetically pure (tested in April 2014[HDM1] ).|
Suitable natural habitat within the indigenous natural range (IDR) is limited to the remaining renosterveld patches and some grassy micro-habitat patches in the fynbos areas of the Overberg region. The extent of occurrence is estimated to be 8,779 km², of which 3,664 km² comprises of remaining natural habitat (GeoTerraImage 2015), which can be construed as the maximum potential area of occupancy (AOO). However, only 623 km² of the preferred renosterveld habitat remains within the natural range, which closely matches the current estimated AOO within the IDR of 602 km². The latter may be an overestimate because only approximately 12% of De Hoop Nature Reserve is actually used by Bontebok (Radloff 2008), and Agulhas National Park currently has very little renosterveld within it. Thus, the amount of utilisable or optimal habitat is both limited and fragmented within the natural range. The AOO estimate increases to 1,153–1,453 km² depending on whether only protected areas, or also private properties are included within the extended natural range.
Preliminary genetic analyses indicate a low genetic variation within the IDR population (van der Walt et al. 2001, 2013). Within the IDR, the subpopulation is fragmented into small subpopulations restricted by fences. Habitat loss within the IDR has been so extensive that the area is estimated to be able to, at best, support 38% of the pre-transformation population potential (Kerley et al. 2003). The poor quality and limited availability of remaining habitat within the IDR necessitated the regulatory extension of their range, which we label here the benign introduction range (BIR) based on the latest Red List guidelines (IUCN Standards and Petitions Subcommittee 2014). This range extension has been spatially modelled to include habitat aspects such as altitude, slope and major preferred vegetation types, within a range which had been demarcated for regulatory purposes, whereby translocations of the subspecies were permitted outside its indigenous range prior to 2012. The BIR has enabled additional utilisation of this subspecies by private land owners and the creation of a buffer population from which to augment subpopulations within the IDR. Both West Coast and Table Mountain National Parks are located within the BIR. To date, however, no reintroductions into IDR protected populations have occurred. For example, Agulhas National Park only has two Bontebok but the long term plan is to source animals for future translocations from Table Mountain and West Coast National Parks. All translocations in the Western Cape are subject to the CapeNature Bontebok Conservation, Translocation and Utilisation Policy (Birss et al. 2013), which requires all proposed Bontebok for translocation to be genetically tested and declared pure before release. Some Bontebok subpopulations in the BIR can be considered ex situ conservation or benign introduction as they are within an environment that is reasonably close to the indigenous range and variables such as winter rainfall, disease, and habitat are considered similar enough to create comparable selection pressures. Additionally, this is a region where spatial separation from Blesbok is feasible, which has specific value in controlling the issuing of permits for Blesbok in this area. Importantly, the population within the IDR is <1,000 mature individuals and thus the BIR concept is a mechanism to support a viable population. However, at present, there is no metapopulation plan to connect subpopulations within the BIR to the IDR and thus the two populations are effectively isolated. Similarly, until genetic testing has been completed for both formally protected and privately protected subpopulations, it is uncertain which subpopulations should form part of the metapopulation. Thus, a precautionary approached is employed in including subpopulations.
Extra-limital subpopulations have been established on private farms or ranches in at least the Eastern Cape, Northern Cape, Free State and North West provinces, and there is pressure to increase the extent of introduction (Power 2014). These extra-limital introductions could be detrimental to the subspecies because Bontebok are adapted to very unique habitat and climatic conditions: the East Coast Renosterveld bioregion receives some rain throughout the year but has a distinct peak during winter with about 65% of rain falling between April and October. These animals thus adapted over at least 20,000 years in isolation from the Highveld-bound Blesbok to a climate of wet and cold winters and warm and dry summers. This is opposite to the conditions experienced by Blesbok that experience warm and wet summers and very cold but dry winters.
Native:South Africa (Eastern Cape Province - Introduced, Free State - Introduced, Northern Cape Province - Introduced, North-West Province - Introduced, Western Cape)
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Due to its restricted range, habitat transformation for agriculture, competition with domestic grazers and over-hunting, the Bontebok population reached a critical low in 1931 when 22 animals were fenced into the newly proclaimed Bontebok National Park (Van Rensburg 1975). Bontebok National Park was proclaimed in the Bredasdorp district with the specific goal of protecting a subpopulation of the subspecies (Barnard and van der Walt 1961). Population numbers increased, but remained below 100 individuals. It was then discovered that the animals at this site suffered from copper deficiency and high parasite infestation, specifically lungworm (Protostrogylus spp.). The park was also very small (6.8 km²) and was extensively covered (80%) by the unpalatable renosterbos (Dicerothamnus rhinocerotis) (Barnard and van der Walt 1961). In 1960, the present site of Bontebok National Park was proclaimed close to Swellendam and 84 Bontebok were translocated there, of which 61 survived (Penzhorn 1971). In the new area, numbers increased to 320 in 1981 with the current subpopulation maintained at around 250 and is currently 190 individuals after an annual off-take in 2014. The combined subpopulation for De Hoop Nature Reserve and neighbouring Denel Overberg Test Range, which is managed as an ecological unit, is currently estimated at 492 individuals, with a maximum of 526 individuals ever recorded. However, this subpopulation is prone to crashes if not managed correctly (Scott 1993). The current subpopulation size for Aghulhas National Park and Salmondsdam Nature Reserve is only two individuals, emphasising the urgent need for a metapopulation plan to create viable subpopulations. |
Based on field surveys and censuses, we can determine the current number of Bontebok with reasonable accuracy. Within the natural distribution range, there are 686 individuals in four formally protected areas (we include the greater De Hoop Area that includes De Hoop Nature Reserve and the privately owned Denel Overberg Test Range here). Subpopulation demographics from Bontebok National Park suggest a mature population structure of 75%, where a 1974 survey tallied 360 animals of which 71 were under two years of age and not deemed sexually mature (De Graaff et al. 1976). Using the figure of 75% thus implies that there are 515 mature individuals within the natural range. If the subpopulations existing on formally protected areas within the benign introduction range are considered, the total mature population size may be considered to be 664. Additionally, there are an observed 219 individuals on 50 private properties within the natural range, which increases the mature population size to 828 individuals. However, some of these subpopulations are intensively managed, or contain hybrids (Birss et al. 2013), and are thus not eligible for inclusion (IUCN Standards and Petitions Subcommittee 2014). For the latter, while both Bontebok National Park and Greater De Hoop Areas subpopulations have been genetically certified as pure, most private properties have not been tested and, of those tested, hybrids have been found (CapeNature unpubl. data). Ongoing testing will determine the number of subpopulations on private properties that are pure and thus eligible for inclusion in the Red List. For the former problem of intensive management, a preliminary analysis to determine which private subpopulations can be considered wild, reveal that 33–39% of private subpopulations are eligible for inclusion in the assessment (based on a sample of N = 18 private subpopulations from across the country, Endangered Wildlife Trust unpubl. data). Depending on whether we extrapolate this proportion to the private farms within the natural and benign introduction range (N = 141 properties) with the most or least abundant subpopulations yields an additional 118–1,272 individuals respectively, and thus 89–954 mature individuals. This increases the mature population range, including all formally protected areas and private subpopulations within both the natural and benign introduction range, to 752–1,618 individuals. However, it is important to note that this estimate does not include the serious threat of hybridisation which might reduce the number of eligible private subpopulations dramatically. The crux of Bontebok conservation is determining genetic purity of its subpopulations and the consensus among the assessors is that population size must be conservatively based on only genetically tested subpopulations that have been shown to be pure.
Overall, the core population within the natural range on protected areas has not increased since the 2004 estimate (Friedmann and Daly 2004), where the total population tallied to 770 individuals compared to 686 individuals in 2014. Outside of the natural and benign introduction range, however, Bontebok subpopulations are increasing. There are an observed 4,857 individuals (existing in extra-limital areas, which are not included in this assessment (IUCN Standards and Petitions Subcommittee 2014). This is probably an underestimate as not all information from the private sector is available. Extra-limital subpopulations are not considered to possess conservation value for reintroduction or supplementation in the natural range. For example, although the Tsolwana Nature Reserve, Eastern Cape, subpopulation was registered as pure Bontebok based on the phenotypic but not genetic assessment (Fabricius et al. 1989), it is not considered an ideal source for reintroductions because the selection pressure outside the natural range may differ significantly. Here, the number of years/generations since departure from the natural range will be important: if it is only a couple of years or generations since departure it might still be an acceptable source for reintroduction providing that the subpopulation was not subjected to selective breeding (Champagnon et al. 2012). Initial indications are that 116 extra-limital subpopulations are from herds that have been registered as pure based on phenotypic traits and another 229 are from herds that have been genetically tested (D. Dalton unpubl. data). These data still need more analysis though as there are a number of owners listed where numbers are not given and it is suspected that a greater proportion may also have been tested and or registered. However, these subpopulations, even if pure, are still of limited conservation value due to the problems associated with re-stocking from extra-limital subpopulations and out-breeding depression (Champagnon et al. 2012). Thus, extra-limital subpopulations of Bontebok, especially if maintained over several generations are of little to no value to Bontebok conservation.
A metapopulation management plan is desperately needed to sustain Bontebok genetic purity and diversity. Within the natural range, there are many small properties containing small subpopulations which cannot increase in size because they are limited by space. In the natural areas, there is a space limitation due to extensive crop production. For example, the average subpopulation size on private properties in the Western Cape is 14 ± 20 individuals (N = 127 properties), compared to 38 ± 36 individuals in the Eastern Cape (N = 69 properties), 28 ± 31 individuals in the Free State (N = 22 properties), and 46 ± 49 individuals in the Northern Cape (N = 27 properties). Of 6,677 individuals estimated to have potentially occurred in the natural range before habitat transformation, only 2,544 individuals are estimated to be able to be supported now (Kerley et al. 2003). Thus, although there is still scope for the core population to increase (currently only 905 individuals in total within the natural range), protected areas and private conservation areas must significantly expand to create larger areas of natural habitat for the population and these should be connected to a wider metapopulation that includes the benign introduction range to become a resilient population.
|Current Population Trend:||Stable|
|Habitat and Ecology:||The historic distribution range of Bontebok is very closely associated with the East Coast Renosterveld bioregion, which comprises four different vegetation types: Western Rȗens Shale Renosterveld (14% remaining), Central Rȗens Shale Renosterveld (13% remaining), Eastern Rȗens Shale Renosterveld (19% remaining) and Mossel Bay Shale Renosterveld (Mucina and Rutherford 2006).|
Bontebok are almost exclusively grazers (Beukes 1984), with a preference for short grass and recently burnt veld (Beukes 1987, Novellie 1987, Kraaij and Novellie 2010). Water is an essential habitat requirement and they stay within 1.5 km from surface water during the dry season (Van Zyl 1978, Luyt 2005, David and Lloyd 2013). Within their natural range on the coastal lowlands, grassy areas are predominantly found in the renosterveld areas but Bontebok also make use of small grassy microhabitats or recently burnt fynbos and strandveld habitats (Scott 1993, Radloff 2008). Suitable habitat for Bontebok is thus predominantly limited to the remaining renosterveld patches in the Overberg region. Fragmented subpopulations are currently found primarily in suboptimal habitat and old cultivated lands where they appear to do relatively well. Bontebok avoid tall woody vegetation with low visibility and areas with steep slopes, preferring open areas with low shrubs (Novellie 1987). Watson et al. (2011) showed that Bontebok are more closely associated with burnt veld than Mountain Zebra in Bontebok National Park. Four to five years post fire they no longer show interest in the burnt vegetation type and revert to grazing lawns of Cynodon dactylon.
A detailed 15-month study of Bontebok behaviour in Bontebok National Park during 1969 and 1970 revealed that the social structure comprises bachelor herds, nursery herds and territorial males (David 1973). Territories were found to be small in size and limited in number, leaving large areas where bachelor herds can roam with little or no harassment. Males defended their territories throughout the year through ritualised chasing and physical fighting was not observed. The average nursery herd size was three adult females with 1.5 lambs. De Graaff et al. (1976) found a similar figure of 3 ± 2.2 (N = 18 herds) females in a breeding herd. Bachelor herds consist of males of all ages older than one year, as well as yearling females (David 1973). Bachelor herd size was 8.5 ± 6.3 (N = 12 herds) in the study of De Graaff et al. (1976) and David (1973) reported as many as 75 animals together. Young males and females leave the nursery herd on their own accord and can remain solitary but usually join bachelor groups (David 1973). Males do not seem to establish territories before the age of five to six years of age and return to bachelor herds once displaced from their territories (David 1973). Bontebok were found to be strong seasonal breeders with the main calving season being September–October and the rutting season from January to mid-March (David 1973).
Ecosystem and cultural services: Bontebok are a flagship subspecies of the Cape Floristic Region, particularly renosterveld, and can be used in ecotourism ventures. Rarity may increase its trophy hunting value, especially that of pure Bontebok.
|Continuing decline in area, extent and/or quality of habitat:||Yes|
|Use and Trade:||
The horns and skins are traded as part of trophy hunts, and live animals are traded at game auctions. Individuals are utilised from captive breeding, ranched (extensive) and wild (formally protected) areas. Activities on private land are mainly for ecotourism, trophy hunting and breeding of trophy animals. As such, the subspecies is widely hunted and traded outside of its natural range where it has increased dramatically in numbers but unfortunately have limited to no conservation value. The translocation of Bontebok and Blesbok outside their natural range is a significant threat to the continued existence of the two subspecies, as hybridisation takes place and becomes increasingly likely. Additionally, there is a concern that there is a net flow of individuals away from the natural range. Western Cape permit data for the last 10 years show that almost 600 animals have been translocated from the natural range and a further 200 from the benign introduction range. Since hunting is not regulated through direct permitting, the number of hunted Bontebok is unknown. Bontebok is a subspecies listed on Certificates of Adequate Enclosures (CoAEs), which means that harvest/hunt/export is not regulated but exempted from separate applications and consequently there is limited regulatory control of subpopulations on private properties (Birss et al. 2013).
At present there has been no reported illegal offtake of Bontebok in any of the national parks or provincial parks where they occur. Given the limited genetic diversity of Bontebok, a strict control of live animal sales needs to be set in place to limit inbreeding in the long term. Additionally, exporting animals outside of the natural range can deplete the genetic pool of the core population and management plans should thus ensure that the translocation of animals, as part of a managed metapopulation, is kept between the natural and benign introduction range.
Farmers saved this subspecies from extinction but modern wildlife ranchers have ambiguous effects on Bontebok conservation. Wildlife ranching is not prominent in the natural range and it appears as if the largely extra-limital industry is impacting negatively on landowners within the natural range who want to contribute to the conservation of the subspecies but increasingly cannot afford to buy and stock Bontebok. The value of the subspecies has increased in the last five years and there is an increasing demand for extra-limital introductions such as in the North West Province (Power 2014). Genetic testing for purity has increased the price and the demand for pure animals. This might act as an incentive to not only conserve the subspecies itself, but also its preferred habitat, the renosterveld, although there is no evidence that this is currently happening in its native range. Prudent veld management is needed in the native range where Bontebok do occur, as improving grass cover within renosterveld might result in the loss of plant species diversity, including species classified as rare or threatened (Novellie and Kraaij 2010). On the negative side, there is evidence that some private landowners deliberately hybridise Bontebok and Blesbok for trophy hunting purposes (Schmidt 1999), and artificial selection for colour morphs and exceptional horn lengths is suspected. The hybrid and artificial selection threat must be curbed through a management plan taken up and enforced by all participating landowners.
The major threats for this subspecies are hybridisation with Blesbok, the lack of available habitat within its natural range (thus limiting population expansion), low genetic diversity, which was probably the result of two bottlenecks caused by overhunting and disease (van der Walt et al. 2001) and poor gene flow between subpopulations. Habitat loss is severe and in some cases irreversible. Although the population size of what we hope is pure Bontebok has increased, it has remained relatively low compared to other ruminants (for example, Broders et al. 1999). The ultimate threat is the indiscriminate and uncontrolled movement of Blesbok, Bontebok and Blesbok/Bontebok hybrids across the country. As such, the exact status of Bontebok and the long term security of the subspecies is still uncertain. Additionally, there is uncertainty over the impact climate change will have, especially in terms of the synergistic threat of habitat loss. The corresponding threats are:
Currently, key protected areas include Bontebok National Park (genetically certified pure subpopulation within the natural range); Table Mountain National Park (genetically certified pure subpopulation within the benign introduction range); De Hoop Nature Reserve and Denel Overberg Test Range (largest subpopulation within the natural range); and Agulhas National Park (potential for significant subpopulation growth within the natural range). Although subpopulations have exhibited positive growth rates, offtakes and translocations from within the natural range have suppressed overall population growth. Similarly, the lack of available habitat within the natural range has inhibited population expansion and an increase in area of occupancy. The net effect is that the core Bontebok population has not increased within the natural range since the 2004 assessment (Friedmann and Daly 2004). To redress this, the main interventions should be the development and implementation of a Biodiversity Management Plan and metapopulation strategy, as well as the acquisition and connection of additional natural habitat within the natural and benign introduction distribution range.
Recommendations for land managers and practitioners:
|Citation:||Radloff, F., Birss, C., Cowell, C., Peinke, D., Dalton, D. & Kotze, A. 2017. Damaliscus pygargus ssp. pygargus. The IUCN Red List of Threatened Species 2017: e.T6236A50185717.Downloaded on 23 July 2018.|
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