Desert Warthog (Phacochoerus aethiopicus)
Fig 1. The somali warthog (Phacochoerus aethiopicus delamerei) is the only living subspecies of desert warthog.
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Taxonomy
The desert warthog (Phacochoerus aethiopicus), is one of two living species of warthog (Phacochoerus spp.), the other being the more well-known common warthog (Phacochoerus africanus). The species was thought extinct after being wiped out in the cape region (7). However, a population originally assigned to the common warthogs in East Africa was reclassified in the 1990s to this species (7), making it a lazarus taxon. This reclassification has since been verified by genetic analysis (7) and the two species of warthog appear to have diverged around 4.5 mya in the Pliocene (7). The second closest relative is the giant forest hog (Hylochoerus meinertzhageni), collectively these species form the Phacochoerini (9, 10). Two subspecies are named for the desert warthog, the first described was the now-extinct cape warthog (P. a. aethiopicus) and the other is the extant somali warthog (P. a. delamerei) (7). Various fossil species are considered junior synonyms of this species including Phacochoerus stenobunus, P. venteri and P. meiringi.
Distribution
The extant population of desert warthog is limited to East Africa with most of the range contained within Somalia and Kenya (1, 3, 6), though populations also occur in Eastern Ethiopia. The Cape warthog was limited to South Africa, particularly the cape region, though occurrences in the karoo are also reported (2). A few dubious historical reports from Southern Namibia would extend the range significantly, these are corroborated by a fossil occurrence too (2). The two desert warthog lineages were connected at some point in the past, but fossil evidence between the cape and horn of Africa is currently lacking, and given that no genetic analysis of the cape specimens is available, (probably due to DNA deterioration) a divergence age between the subspecies is impossible to estimate. It is entirely possible that the desert warthog was once a widespread species that has heavily declined, though that is largely conjecture.
Fig 2. IUCN Ranges of the desert warthog (Phacochoerus aethiopicus) in blue and the common warthog (Phacochoerus africanus) in red, with a purple overlap zone. As seen there are small areas of sympatry but the general range division may indicate a high degree of competition (4). Fossil locations of Phacochoerus are indicated, however in most cases remains are not distinguished between the two species. Cape fossils constituted desert warthog remains.
Ecology and Morphology
The species is slightly smaller than the common warthog (1), averaging around 71kg (8). The desert warthog can be most readily distinguished from its more common relative by the lack of incisors (7), though in some cases vestigial incisors can be found in the lower jaw (1). The proportions of the skull vary somewhat from the common warthog. Most easily identifiable are external differences: The ‘warts’ are hooked downwards in extant desert warthogs (1), the area immediately beneath the eyes is swollen and the ears tips are bent backward (2). The two species are very similar on the whole (1).
The ecology of the desert warthog is not well studied. The modern population is, despite the name, not a true desert specialist, occurring in areas with between 100 and 600mm of annual rainfall, it is absent from the very driest regions of the horn of Africa (1). Nevertheless, it is restricted to arid regions and doesn’t appear to be viable in the wetter regions, probably because it is outcompeted by the common warthog in these areas (1). Likewise, the species appears absent in highland areas, where the common warthog is present (1). This would indicate that the two species are somewhat competitively exclusive, but they do co-occur in a few areas (3). The cape warthog was present in relatively wet areas such as the Eastern Cape until the 19th century (2), so the arid specialization may be unique to the Somali subspecies. The preferred habitats of the Somali warthog appear to range from dry steppe to arid bushland and even open woodland, though it notably does not occur in forests (4). A study has been carried out inferring diet from carbon-13 concentrations in both cape and Somali desert warthog bones as well as the common warthog, which suggests that the desert warthog relies heavily on grazing, with no major differences in diet composition between Eastern and cape populations. This makes it somewhat different from the common warthog which is more generalistic and integrates browsing in its diet (5). the desert warthog has been observed supplementing its grazing with invertebrates, fruits, roots, and other vegetation (4).
The desert warthog shares its habitat in the horn of Africa with various other megafaunal herbivores including the African elephant (Loxodonta africana), giraffe (Giraffa camelopardalis) African wild ass (Equus africanus), both the grevy’s (Equus greyvi) and plains zebra (Equus quagga) and a number of antelope species, however, most of these range overlaps are restricted to a few areas in Kenya. During the Pleistocene, it may also have occurred alongside Elephas iolensis in the horn of Africa. In terms of potential predators, the lion (Panthera leo), leopard (Panthera pardus), cheetah (Acionyx jubatus) spotted hyena (Crocuta crocuta) and African wild dog (Lycaon pictus) all occur alongside the desert warthog and are likely predators. Though no literature specific to the species exists on the predators so far, lions and leopards, in particular, are key predators of the common warthog and may also be the case for desert warthogs (5). The faunal assemblage in the Holocene cape would have been similar, though most of the megafaunal species once present are now extinct.
Citations
1. D’Huart, J-P., Grubb, P.. (2001). Distribution of the common warthog (Phacochoerus africanus and the desert warthog (Phacochoerus aethiopicus) in the Horn of Africa. African journal of Ecology 39, 156-169.
2. Grubb, P., d’Huart, J-P.. (2010). Rediscovery of the Cape Warthog Phacochoerus aethiopicus: A review. Journal of East African Natural History 99(2), 77-102.
3. De Jong, Y.A., Butynski, T.M.. (2014). Distribution, abundance, ecology, and conservation status of the desert warthog (Phacochoerus aethiopicus) in northern Kenya. National Geographic Society , Washington D.C.
4. de Jong, Y.A., Butynski, T.M. & d'Huart, J.-P. (2016). Phacochoerus aethiopicus (errata version published in 2016). The IUCN Red List of Threatened Species 2016.
5. Nyafu, K.. (2009). Warthog as an introduced species in the Eastern Cape. Masters Thesis, Nelson Mandela Metropolitain University.
6. Obanda, V. O., Lekolool, I., Munyao, M., Chege, S. M., Manyibe, T., Gakuya, F.. (2011). New distribution records for the desert warthog (Phacochoerus aethiopicus delamerei – Pallas 1766)
7. Randi, E., D’Huart, J-P., Lucchini, V., Aman, R.. (2002). Evidence of two genetically deeply divergent species of warthog, Phacocheorus africanus and P. aethiopicus (Artiodactyla: Suiformes) in East Africa. Mammalian Biology 76, 91-96.
8. Faurby, S., Pedersen, R. Ø., Davis, M., Schowanek, S. D., Jarvie, S., Antonelli, A., & Svenning, J.C. (2020). PHYLACINE 1.2.1: An update to the Phylogenetic Atlas of Mammal Macroecology. doi:10.5281/zenodo.3690867
9. Frantz, L., Meijaard, E., Gongora, J., Haile, J., Groenen, M.A.M., Larson, G.. (2016). The Evolution of Suidae, Annual review of animal biosciences 4(1), 61-85.
10. Gongora, J., Cuddahee, R.E., Nascimento, F.F.d., Palgrave, C.J., Lowden, S., Ho, S.Y.W., Simond, D., Damayanti, C.S., White, D.J., Tay, W.T., Randi, E., Klingel, H., Rodrigues-Zarate, C.J., Allen, K., Moran, C., Larson, G. (2011). Rethinking the evolution of extant sub-Saharan African suids (Suidae, Artiodactyla). Zoologica scripta, 40, (4). 327-335.