In the previous article we looked at the proposal that the various babirusa taxa – long regarded as subspecies – deserve to be raised to species rank. The argument goes that the taxa concerned are (1) morphologically diagnosable, (2) ‘as distinct’ as are other taxa traditionally regarded as species (raising the taxa to species level therefore represents a sort of attempt at uniformitarianism), and (3) represent distinct phylogenetic lineages. Meijaard & Groves’s proposal therefore reflects their adherance to the phylogenetic species concept, or PSC (where distinct lineages on a cladogram have to be regarded as distinct taxa), and should not be regarded as mere subjective ‘splitting’. Predictably, any suggestion that a traditional ‘species’ – like Babyrousa babyrussa – should be split into several or many has resulting in some criticism (see the Tet Zoo comments here and here).
Are criticisms like this justifiable? We begin with the observation that the division of a traditional ‘species’ (like Babyrousa babyrussa) into several ‘phylogenetic species’ reverses the trend of the early 20th century: at this time, multiple large mammal species previously erected by Victorian (and earlier) naturalists were lumped together.
It now seems that at least some of this lumping was over-zealous and in fact rather lazy, and it’s for this reason that I refer to it as laissez-faire lumping. This opinion is not my own: I have been inspired by such mammalogists as Colin Groves, Peter Grubb, Jeheskel Shoshani and Esteban Sarmiento. In arguing that the two African elephant species Loxodonta africana and L. cyclotis should be separated as distinct species, Grubb et al. (2000) wrote…
‘Biodiversity of large mammals is severely underestimated. The existence of a narrow hybrid zone among large mammals can be detected in casual field surveys, which is not the case for small mammals and other animals that have to be trapped for close investigation. This simple fact has led to the downgrading of perfectly distinct, diagnosable species to a level where they become taxonomically ‘invisible’ and thus lost to biodiversity studies. There are many examples of large mammal genera in which single species are currently supposed to extend through forest and savannah zones (as in the elephant case treated here), and this series of case studies might be a place to start testing the proposition that their biodiversity has been underestimated’ (p. 3).
Besides African elephants, laissez-faire lumping has recently been asserted for giraffes (Brown et al. 2007), the Potamochoerus bushpigs and river hogs (Grubb 1993, Groves 2000), the wild pigs of the Philippines (Oliver 1995, Groves 1997), warthogs (Grubb 1993, Randi et al. 2002), the African buffaloes traditionally placed together in Syncerus caffer (Grubb 1972, Groves 2000), the bushbucks traditionally grouped together as Tragelaphus scriptus (Grubb 1985, Groves 2000), the red deer and wapiti traditionally grouped together as Cervus elaphus (Geist 1999), gorillas (Groves 1996, Sarmiento & Butynski 1996, Sarmiento & Oates 2000), orangutans (Xu & Arnason 1996), wolves (Grewal et al. 2004, Kyle et al. 2006, Aggarwal et al. 2007) and many others [images at left: how many species do you see?].
While biologists tend to be harshly critical of workers who erect new taxa based on only small apparent differences (such workers become known as ‘splitters’), there is far less criticism of those who indulge in laissez-faire lumping: it’s almost as if the lumpers are regarded as the ones with the most realistic handle on species-level biodiversity. But are they? Well, as African elephants and the various other examples cited above seem to indicate, perhaps they aren’t in all cases. Indeed, we should be as sceptical of lumping as we are of splitting. Such things as the several proposed babirusa species, the different warthogs, and the gorilla and African buffalo species are all morphologically distinct, and arguably ‘as distinct’, or ‘more distinct’, as are long-recognised species accepted without question in other groups (I’m looking at such passerines as Dendroica and Empidonax… shudder).
Kill subspecies, kill species… time to move on?
One reason that a lot of people dislike ‘phylogenetic species’ is that such entities often differ from the species recognised by tradition. But this is because ‘phylogenetic species’ and ‘traditional species’ are not really the same thing: ‘phylogenetic species’ are (so far as I understand from the writings of Joel Cracraft and others) meant to respond to irreducible clusters of individuals: that is, to the smallest distinct subdivision of a given taxon. The conventional idea of a species is actually something rather vaguer: it usually encapsulates some subjective notion of similarity (e.g., population A and B belong to the same species because they’re ‘similar enough’ and can probably interbreed).
Perhaps the tidiest solution is simply to do away with the notion of species and subspecies entirely and work with something else, such as the ‘least inclusive taxonomic units’ of Pleijel & Rouse (2000). Sluys & Hazevoet (1999) argued that we should be naming diagnosable phylogenetic entities, and that traditional concepts of ‘species’ and ‘subspecies’ were misleading and carried too much historical baggage to be reliable.
One problem with all of this is that – for some of the taxa concerned (I’m bringing it back to babirusas now) – all too little work has been done on phylogenetic structure and so on. The proposal that ‘Babyrousa babyrussa‘ of traditional includes several, morphologically distinct lineages that deserve to be recognised as ‘species’ is based on the morphological differences observed between these respective populations. The idea that these warrant recognition as distinct taxonomic entities may well be valid, but it’s a hypothesis and we need more information before we can be confident that we’re not being confused by something else, like the sort of ecomorphological plasticity present in some species (like Lions Panthera leo). However, remember that we discover more by assuming less: many of us make conclusions about megamammal taxonomy based on assumptions (e.g., that more than one living elephant species in Africa is too many*), not on the data that now bears on the issue.
* I never understand arguments like this, given that the modern world is horribly impoverished compared to the situation of just a few hundred thousand years ago.
Finally, what’s with the photos used at the top?, I hear you cry. Both photos are of the Golden babirusa or Hairy babirusa B. babyrussa specimen on display at the Raffles Museum of Biodiversity Research (photos kindly provided by Ivan of The Lazy Lizard’s Tales). It was killed on Buru and donated to the museum in 1913 by G. P. Stubbs. Virtually all other photos out there are of the more naked-skinned B. celebensis, so I was very excited to see these pictures. The animal’s blonde pelt is particularly striking (though note that I’ve tinkered with the contrast a bit).
This is NOT ALL on babirusas! They will return!!
For previous babirusa articles see…
- The deer-pig, the Raksasa, the only living anthracothere… welcome to the world of babirusas
- Are anthracotheres alive and well and living on Sulawesi? No, but it was a nice idea. Babirusas, part II
- What’s with the bizarre curving tusks? Babirusas, part III
- When babirusas fight (babirusas, part IV)
- This little piggy went ploughing (babirusas, part V)
- The many babirusa species (babirusas, part VI)
For other Tet Zoo articles on artiodactyls see…
- McGowan’s mystery bovid
- The legend of Hogzilla
- Welcome…. to the world of sheep
- Return…. to the world of sheep
- Tet Zoo picture of the day # 23 [on entelodonts]
- Deer oh deer, this joke gets worse every time I use it
- Duiker, rhymes with biker
- Sable antelopes and the miseducation of youth
- Giant killer pigs from hell
- The plasticity of deer
- Over 400 new mammal species have been named since 1993
- Great Asian cattle
- Stuffed megamammal week, day 1: Khama
- Stuffed megamammal week, day 2: Eland
- Stuffed megamammal week, day 3: Okapi
- Death by lightning for giraffes, elephants, sheep and cows
- Dromomerycids: discuss
Refs – –
Aggarwal, R., Kivisild, T., Ramadevi, J., & Singh, L. (2007). Mitochondrial DNA coding region sequences support the phylogenetic distinction of two Indian wolf species Journal of Zoological Systematics and Evolutionary Research, 45 (2), 163-172 DOI: 10.1111/j.1439-0469.2006.00400.x.
Brown, D. M., Brenneman, R. A., Koepfli, K.-P., Pollinger, J. P., Milá, B., Georgiadis, N. J., Louis, E. E., Grether, G. F., Jacobs, D. K. & Wayne, R. K. 2007. Extensive population genetic structure in the giraffe. BMC Biology 2007, 5: 57 doi:10.1186/1741-7007-5-57
Geist, V. 1999. Deer of the World. Swan Hill Press, Shrewsbury.
Grewal, S. K., Wilson, P. J., Kung, T. K., Shami, K., Theberge, M. T., Theberge, J. B. & White, B. N. 2004. A genetic assessment of the Eastern wolf (Canis lycaon) in Algonquin Provincial Park. Journal of Mammalogy 85, 625-632.
Groves, C. P. 1996. Do we need to update the taxonomy of gorillas? Gorilla Journal 12, 3-4.
– . 1997. Taxonomy of wild pigs (Sus) of the Philippines. Zoological Journal of the Linnean Society 120, 163-191.
– . 2000. What are the elephants of west Africa? Elephant 2, 7-8.
Grubb, P. 1972. Variation and incipient speciation in the African buffalo. Zeitschrift für Säugetierkunde 37, 121-144.
– . 1985. Geographical variation in the bushbuck of eastern Africa (Tragelaphus scriptus; Bovidae). In Schuchmann, K.-L. (ed) Proceedings of the International Symposium on African Vertebrates: Systematics, Phylogeny and Evolutionary Ecology. Zoologisches Forchungsinstitut und Museum Alexander Koenig (Bonn), pp. 11027.
– . 1993. The Afrotropical suids: Potamochoerus, Hylochoerus and Phacochoerus. In Oliver, W. L. R. (ed) Pigs, Peccaries and Hippos Status Survey and Action Plan. IUCN/SSC Pigs and Peccaries Specialist Group & IUCN/SSC Hippos Specialist Group (Gland, Switzerland), pp. 66-75.
– ., Groves, C. P., Dudley, J. P. & Shoshani, J. 2000. Living African elephants belong to two species: Loxodonta africana (Blumencah, 1797) and Loxodonta cyclotis (Matschie, 1900). Elephant 2, 1-4.
Kyle, C. J., Johnson, A. R., Patterson, B. R., Wilson, P. J., Shami, K., Grewal, S. K. & White, B. N. 2006. Genetic nature of eastern wolves: past, present and future. Conservation Genetics 7, 273-287.
Oliver, W. L. R. 1995. The taxonomy, distribution and status of Philippine wild pigs. Ibex J.M.E. 3, 26-32.
Pleijel, F. & Rouse, G. W. 2000. Least-inclusive taxonomic unit: a new taxonomic concept for biology. Proceedings of the Royal Society, London B 267, 627-630.
Randi, E., d’Huart, J. P., Lucchini, V. & Aman, R. 2002. Evidence of two genetically deeply divergent species of warthog Phacochoerus africanus and P. aethiopicus (Artiodactyla: Suiformes) in East Africa. Mammalian Biology 67, 91-96.
Sarmiento, E. & Butynski, T. 1996. Present problems in gorilla taxonomy. Gorilla Journal 12, 5-7.
– . & Oates, J. F. 2000. The Cross River gorillas: a distinct subspecies, Gorilla gorilla diehli Matschie 1904. American Museum Novitates 3304, 1-55.
Sluys, R. & Hazevoet, C. J. 1999. Pluralism in species concepts: dividing nature at its diverse joints. Species Diversity 4, 243-256.
Xu, X. & Arnason, U. 1996. The mitochondrial DNA molecule of Sumatran orangutan and a molecular proposal for two (Bornean and Sumatran) species of orangutan. Journal of Molecular Evolution 43, 431-437.