The Arabian gazelle as a peninsular counterpart for that obscure gazelle-relative, the dibatag of Africa

I have pointed out, in a previous post, that the large animals of the Arabian Peninsula are consistently smaller than their closest relatives (usually of the same species or genus) on the mainland of Africa and/or Asia. Since the largest animals of islands worldwide tend to be small relative to comparable animals on relevant mainland areas, the Arabian Peninsula seems to act biogeographically like an island -which is surprising in view of its vast area and its broad connection to Asia.

Here I focus on what is perhaps the most complicated example of this pattern: the Arabian gazelle (Gazella arabica). This species, the adult female of which weighs only 10-15 kg, is restricted to the Arabian Peninsula and was formerly widespread on stony slopes with scattered thorny shrubs.

The other two species of Gazella of the Arabian Peninsula are easy to compare with mainland counterparts. Gazella marica is a diminutive (adult female 15-20 kg) version of Asian Gazella subgutturosa, and extinct Gazella saudiya is a slightly diminutive (adult female probably about 13 kg, making it the smallest of all gazelles) version of African Gazella dorcas.

What is odd about the Arabian gazelle is that it seems to be the diminutive counterpart of an antilopin belonging to a a genus restricted to Somalia and Ethiopia and containing only one species: the dibatag (Ammodorcas clarkei). The dibatag (adult female about 25 kg, with proportionately longer neck and legs than in any gazelle) is so different from the Arabian gazelle that their biogeographical relationship may not previously have been noticed. However, both the seldom-photographed dibatag and the frequently-photographed Arabian gazelle have the neck and legs so elongated that - particularly when they stand bipedally - they can reach higher than competing gazelles to eat from the scattered trees of the semi-desert.

The Horn of Africa, home to the dibatag, is like Arabia in projecting into the Indian Ocean. However, it does not qualify as a peninsula. Hence - so the hypothesis goes - the dibatag can afford to be specialised in body-form, as well as relatively large.

In the conventional view, the Arabian gazelle is merely a gracile-looking southern replacement for the mountain gazelle (Gazella gazella) of the Levant, with which it continues to be taxonomically confused. But another, perhaps more mentally stimulating, view of the Arabian gazelle is as a peninsular ecological counterpart for the dibatag of Africa.
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Posted by milewski milewski, March 13, 2021 11:19

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