Kobus kob kob as the West and Central African counterpart for the common impala (Aepyceros melampus), part 1

INTRODUCTION

The distribution ranges of Kobus kob (the kob) and Aepyceros melampus (the common impala) are mutually exclusive.

Both species

• are medium-sized, evenly-proportioned, brown antelopes with moderate sexual dimorphism (horns restricted to males), and
• eat mainly grass, are gregarious and active mainly diurnally, and have a territorial sociosexual system.

Kobus kob occurs in the Guinea savannas of West and north-central Africa and South Sudan (https://upload.wikimedia.org/wikipedia/commons/8/81/Kobus_kob_distribution.svg). Aepyceros melampus occurs in the savannas of southern and East Africa, favoring thorn savanna over miombo woodland (https://upload.wikimedia.org/wikipedia/commons/e/e4/Impala.png).

This biogeographical and ecological separation suggests that the two taxa share a single niche in a loose sense, partitioning Africa so that one or the other occupies any given area.

The most important evidence of this is that A. melampus, although abundant in East and southern Africa, is absent across the vast savannas of the other half of the continent.

Given this scenario of approximate ecological equivalence, it is worth comparing Kobus kob (https://www.alamy.com/stock-photo-kob-standing-on-meadow-kobus-kob-35643086.html?imageid=5D86534C-0804-4455-AB6C-6B9B0A715441&p=89982&pn=7&searchId=998dfc7baffa23b9177357f935dc7ab5&searchtype=0) with A. melampus in various biological features.

More particularly, in this Post I focus on the most widespread subspecies, namely Kobus kob kob (https://www.alamy.com/stock-photo-kob-hind-kalakpa-resource-reserve-eastern-region-ghana-11380712.html?imageid=FF4E82D8-7D10-4CD4-876F-CC9B10B86B39&p=54834&pn=8&searchId=1cc4c968aae75dd56f77ec944b83ce3f&searchtype=0).

This, the nominate subspecies, occurs from Senegal (https://en.wikipedia.org/wiki/Senegal) in the west to Chad (https://en.wikipedia.org/wiki/Chad) in the east, a distance of nearly 5,000 kilometers - entirely devoid of any species of Aepyceros.

AIMS

So, the central question is:
To what degree is K. kob kob (https://www.inaturalist.org/observations/149939631) just a 'western/northern impala', under a different name?

For illustrations of Aepyceros melampus, see my many Posts (https://www.inaturalist.org/posts/89229-an-index-to-my-posts-about-impalas-aepyceros#).

PHYLOGENY

Kobus belongs to the tribe Reduncini, whereas Aepyceros belongs to the tribe Aepycerotini. This means that

• they have distinct evolutionary histories (https://www.sciencemagazinedigital.org/sciencemagazine/21_june_2019/MobilePagedArticle.action?articleId=1498484#articleId1498484), and
• any detailed resemblances reflect evolutionary convergence, rather than common ancestry.

BODY MASS AND PROPORTIONS

Kobus kob kob is similar in body mass to Aepyceros melampus.

Important for this comparison is the fact that K. k. kob is much smaller than K. k. thomasi, a better-known subspecies occurring in Uganda (pages 191-195 in 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).

The similarity in body size can be illustrated indirectly by using Bubulcus ibis for scale (https://www.alamy.com/stock-photo-kob-hind-with-fawnabout-to-drink-at-waterhole-kalakpa-resource-reserve-11380714.html?imageid=6CD38FB4-8588-4ED5-B0E2-E71CD5E6DCE9&p=54834&pn=7&searchId=b27cc7ee52bb614a82ca2293933ebfc9&searchtype=0 and https://www.gettyimages.com.au/detail/video/impala-male-and-baby-grazing-with-cattle-egrets-stock-video-footage/153421309?adppopup=true and https://www.alamy.com/male-impala-antelope-cattle-egret-moremi-np-africa-image360686597.html).

Kobus kob kob differs from A. melampus in

• being slightly stockier/more thickset (https://www.inaturalist.org/observations/72621322 and https://www.inaturalist.org/observations/116590720), and
• having the rump higher than the withers (https://www.inaturalist.org/observations/195594076), as opposed to the relatively level silhouette of A. melampus (https://www.shutterstock.com/image-photo/impala-grazing-green-1058317634 and https://www.shutterstock.com/image-photo/impala-antelope-ram-large-curved-horns-13608460).

Infants of K. k. kob are far less 'leggy' than those of A. melampus. Please compare https://www.inaturalist.org/observations/81449293 with https://www.shutterstock.com/image-photo/young-impala-aepyceros-melampus-south-luangwa-2433231493, and also see https://www.inaturalist.org/observations/66469668 and https://www.inaturalist.org/observations/19289953.

Form of horns

The horns are similar in size and shape in the two taxa (https://www.inaturalist.org/observations/66512647).

https://www.alamy.com/stock-photo-western-kob-at-rivers-edge-in-senegal-78838761.html?imageid=1AE1F681-9AE9-4852-A3C2-7BA238A29E24&p=141448&pn=1&searchId=699e1dc9f674152eb01f429e99e5e52d&searchtype=0

Sexual dimorphism

The degree and nature of sexual dimorphism are similar in K. k. kob and A. melampus.

ANATOMICAL DETAILS

Hooves

The hooves of K, k. kob are larger than those of A. melampus. The difference is particularly great in the case of the false hooves/dewclaws, which are well-developed in the former, but absent in the latter.

Stifle-fold

In both K. k. kob and A. melampus, dark bare skin shows at the stifle-fold. However, this is far less extensive in the former (https://www.inaturalist.org/observations/153171326 and https://www.inaturalist.org/observations/194064714) than in the latter (https://es.123rf.com/photo_19382128_impala-ram-aepyceros-melampus--kruger-national-park-south-africa.html).

Rhinarium

In both K. k. kob and A. melampus, the rhinarium is small. However, the latter is extreme in this respect (https://www.shutterstock.com/image-photo/male-impala-lying-on-ground-his-1389971402)

Tail

In both K. k. kob and A. melampus, the tail

• is never fully erected in alarm, and
• tends to be tucked (https://www.inaturalist.org/observations/49107470).

Udder

In both K. k. kob and A. melampus, there are two pairs of teats (mammillae).

GLANDS

In both K. k. kob and A. melampus, external glands are poorly-developed relative to most other ruminants, and interdigital and caudal glands are absent.

However, the two taxa differ in that

• preorbital glands are present (small) in K. k. kob, as opposed to absent in A. melampus,
• K. k. kob possesses inguinal glands, instead of the metatarsal glands possessed by A. melampus.

COLOURATION

Both K. k. kob and A. melampus are whitish on the ventral surface of the torso, and the inner surface of the upper hindlegs (https://www.inaturalist.org/observations/87964267). In K. k. kob, the posterior surface of the upper foreleg is whitish (https://www.inaturalist.org/observations/45489988 and https://www.inaturalist.org/observations/174890117 https://www.flickr.com/photos/anymotion/6805172099). However, in the latter this is crisply-defined.

Overall

Both K.k. kob and A. melampus

• have fairly plain colouration (https://www.inaturalist.org/observations/75651690 and https://www.inaturalist.org/observations/75651656 and https://www.inaturalist.org/observations/6741507 and https://www.inaturalist.org/observations/557943)
• with the haunches and ventral part of the flanks relatively pale (https://www.inaturalist.org/observations/150389000).

However, the tone on the flanks is far less distinctly defined in K. k. kob (https://www.inaturalist.org/observations/7108295) than in A. melampus ().

Forelegs

In K. k. kob, dark pelage accentuates the anterior surface of the legs, particularly the forelegs (https://www.inaturalist.org/observations/149566968). In A. melampus, such accentuation is minimal, being restricted to the fetlocks, and absent from most individuals.

Buttocks

Kobus kob kob and A. melampus differ categorically w.r.t. the pattern of colouration on the buttocks (compare https://www.inaturalist.org/observations/174890113 and https://www.inaturalist.org/observations/149939632 with https://www.hlasek.com/aepyceros_melampus_db2745.html and https://www.alamy.com/impala-aepyceros-melampus-male-ram-antelope-portrait-and-close-up-in-wild-of-madikwe-game-reserve-south-africa-image224844451.html).

https://www.inaturalist.org/observations/103751818

Tail
https://www.inaturalist.org/observations/137559365

The tail shows a dark/pale contrast when swished, in both K. k. kob and A. melampus. However, this accentuation is minimal in the former (compare https://www.inaturalist.org/observations/193968110 and https://www.inaturalist.org/observations/110734207 with https://www.shutterstock.com/image-photo/antelope-masai-mara-kenya-2269362071 and https://upload.wikimedia.org/wikipedia/commons/d/d3/ImpalaSerengetiNationalParkMar2011.jpg and https://www.alamy.com/herd-or-harem-of-female-impala-aepyceros-melampus-signal-by-wagging-their-tails-together-in-greater-marakenyaafrica-image178986280.html).

Ear pinnae

In both K. k. kob and A. melampus:

• The anterior surface of ear pinnae is densely covered by whitish hairs. However, a difference is that the dark hairs at the apex are minimal in the former (https://www.inaturalist.org/observations/174890093), as opposed to conspicuous in the latter.

• The apex of the posterior surface of the ear pinna tends to be dark (https://www.inaturalist.org/observations/121639160
  and https://www.inaturalist.org/observations/103751917). However, this pattern is less distinct in the former than in the latter, and tends to disappear in mature males of K.k. kob (https://www.inaturalist.org/observations/6572131).

https://www.inaturalist.org/observations/196323998

https://www.inaturalist.org/observations/152317862

https://www.inaturalist.org/observations/196137319

https://www.inaturalist.org/observations/191558533

https://www.inaturalist.org/observations/174890112

https://www.inaturalist.org/observations/174890101

https://www.alamy.com/herd-of-kob-crosses-a-dirt-road-in-mole-national-park-northern-ghana-image1833506.html?imageid=99F9467D-9044-45DF-B5B1-01E5AAA1A2B3&p=54834&pn=7&searchId=b27cc7ee52bb614a82ca2293933ebfc9&searchtype=0

https://www.alamy.com/kob-hind-and-fawn-disturbed-at-a-salt-lick-mole-national-park-northern-image1833508.html?imageid=5BE18701-13D7-491E-9BCB-4940D6D1E1B3&p=54834&pn=7&searchId=b27cc7ee52bb614a82ca2293933ebfc9&searchtype=0

https://www.inaturalist.org/observations/44762435 and https://www.inaturalist.org/observations/44762434

https://www.inaturalist.org/observations/75651701 and https://www.inaturalist.org/observations/75651699

https://www.alamy.com/kob-antelopes-kobus-kob-on-the-plains-of-simenti-with-a-group-of-baboons-papio-papio-niokolo-koba-national-park-unesco-world-heritage-site-image262934271.html?imageid=CFA08DD2-B646-4FA7-B3BA-66E16DEDBE0D&p=269369&pn=7&searchId=998dfc7baffa23b9177357f935dc7ab5&searchtype=0

Both K. k. kob and A. melampus possess a pedal flag, consisting of pale pasterns offset by dark (https://www.inaturalist.org/observations/129691858 and https://www.inaturalist.org/observations/103751848 and https://www.inaturalist.org/observations/103751810 and https://www.inaturalist.org/observations/103751802 and https://www.inaturalist.org/observations/75651674 and https://www.inaturalist.org/observations/75651671 and https://www.inaturalist.org/observations/36994608 and https://www.inaturalist.org/observations/6443432).

Crook-of-throat

In both K. k. kob and A. melampus, mature males possess a whitish patch on the anterior surface of the neck, adjacent to the lower jaw (https://www.alamy.com/ugandan-kobs-kobus-kob-thomasi-mating-behavior-sequence-queen-elizabeth-national-park-uganda-image376770532.html?imageid=0EC4CE3B-937F-4462-ABAE-3E9F321FD031&p=1132882&pn=1&searchId=8ba2a2cdf722c8a88018f6cc5e319bd5&searchtype=0).

This feature

• is moderately sexually dimorphic, emphasising the masculine brawniness of the neck, and
• is conspicuous enough to qualify as a gular semet/flag.

https://www.inaturalist.org/observations/34206853

to be continued in https://www.inaturalist.org/journal/milewski/90896-kobus-kob-kob-as-the-west-and-central-african-counterpart-for-the-common-impala-aepyceros-melampus-part-2#...

Posted on March 13, 2024 12:24 AM by milewski