Building a search-image for three species of blue duiker

An approximate map of the distributions of the various subspecies of the blue duiker (Philantomba monticola) is in http://africatrophyhunting.com/plains-category/duiker-blue-zanzibar/. I see two main disjunctions, namely the gap between Zimbabwe and Malawi and the gap between the East African coast and the Ugandan region. Should the blue duiker be split into three species accordingly?

Groves and Grubb (2011 https://zmmu.msu.ru/files/%D0%91%D0%B8%D0%B1%D0%BB%D0%B8%D0%BE%D1%82%D0%B5%D0%BA%D0%B0%20%D0%9F%D0%B0%D0%B2%D0%BB%D0%B8%D0%BD%D0%BE%D0%B2%D0%B0/grubb-groves-2011_taxonomy_ungulates.pdf), despite splitting the blue duiker into ten species, regard the East African coastal form as a mere subspecies of aequatorialis of Congo-Uganda. This seems odd in terms of discontinuity of distribution and patterns of colouration.

Groves and Grubb focussed on chromatic distinctions between fawn and grey which may possibly be more distraction than taxonomically significant. Because the visual systems of neither duikers nor their predators are sensitive to hues, such variation can be thought of as 'genetic drift' rather than adaptation. It is the tonal (dark/pale), not the chromatic ('red'), aspects of colouration that are likely to be adaptively significant (i.e. produced by natural selection) and thus most indicative of speciation.

The taxa congicus, melanorheus and aequatorialis of equatorial Africa, from Cameroon to western Kenya, possess a horizontal dark/pale contrast (ineptly described as a 'stripe' by Groves and Grubb) on the hindquarters. See https://www.zoochat.com/community/media/blue-duiker-krefeld-7th-september-2014.272820/ and https://www.biolib.cz/en/image/id222738/ and https://www.zoochat.com/community/media/blue-duiker-colchester-13th-january-2018.384668/. In coastal East Africa there is hardly a trace of this feature (see https://www.mindenpictures.com/stock-photo-blue-duiker-philantomba-monticola-grazing-jozani-national-park-naturephotography-image00544058.html and https://www.larsfoto.se/en/gallery/bird-images-from-foreign-trips/zanzibar-and-pemba/9793-blue-duiker). The difference is one of kind rather than degree. So I suspect that sundevalli, far from being a mere variant of aequatorialis, is not even the same species.

Another example of too much variation to be plausible within a single species is in the colouration of the feet (which are not even mentioned by Groves and Grubb 2011). See https://www.agefotostock.com/age/en/details-photo/blue-duiker-on-meadow-cephalophus-monticola-philantomba-monticola/SSJ-114438/1 and https://www.agefotostock.com/age/en/details-photo/blue-duiker-cephalophus-monticola-philantomba-monticola/RDC-ad_75446/1 and https://www.agefotostock.com/age/en/details-photo/blue-duiker-on-meadow-cephalophus-monticola-philantomba-monticola/SSJ-114437/1 . The markings on the feet are faint but seem absent in most other forms of the blue duiker. Unfortunately I do not know where the animals in these photos come from.

My criticism of Groves and Grubb in the case of the blue duiker is not so much that they over-split but that they may not have made the right splits.

I offer the following search-image to naturalists. It may be possible to distinguish 1) a southern species, from South Africa to Zimbabwe, 2) an East African coastal species extending inland to Malawi, and 3) a widespread species of the central rainforest block and surrounding savanna/forest mosaics including Zambia.

For those keen to 'get their eye in', please practice on https://www.picuki.com/media/1885413740214371768 and https://www.agefotostock.com/age/en/details-photo/duikers-cephalophus-sp-bovidae/DAE-11169243/1 and the photos linked in my first comment below.

Publicado por milewski milewski, 07 de julio de 2021

Comentarios

Agregar un comentario

Acceder o Crear una cuenta para agregar comentarios.