Pictures worth a thousand words, on the theme of adaptively conspicuous darkness in large mammals and birds

@matthewinabinett @zarek @paradoxornithidae @tonyrebelo @jeremygilmore @botswanabugs

The following photos inadvertently show various points about a certain theme in adaptive colouration, viz. conspicuous darkness in aid of society.

The FIRST PHOTO (https://www.gettyimages.ie/detail/photo/cheetah-is-checking-the-menu-royalty-free-image/576417193?adppopup=true) is in the open vegetation of the Serengeti ecosystem.

The species featured are the carnivore Acinonyx jubatus, the gazelle Eudorcas thomsoni nasalis, and the alcelaphin Connochaetes mearnsi.

both this gazelle and this alcelaphin have adaptively conspicuous colouration. In the case of E. t. nasalis, there is a bold pattern of banding on the torso; in the case of C. mearnsi, the whole figure is conspicuously dark, and seems to get darker with distance from the observer (https://www.gettyimages.ie/detail/photo/cheetah-hunting-wildebeest-in-masai-mara-royalty-free-image/136981303?adppopup=true).

The carnivore in this scene is, understandably, inconspicuous in its colouration (https://www.gettyimages.ie/detail/photo/young-african-cheetah-on-grass-royalty-free-image/1354142689?adppopup=true). However, it possesses several flags, which are relatively small-scale features that signal to other carnivores in certain circumstances and perspectives.

In this case, the flags in view are the auricular flag and the caudal flag of A. jubatus.

The SECOND photo (https://www.gettyimages.ie/detail/photo/lion-in-ngorongoro-crater-royalty-free-image/556269039?adppopup=true) extends the themes mentioned above.

The species featured are the carnivore Panthera leo, the bovin Syncerus caffer, the alcelaphin C. mearnsi, and the equid Equus quagga boehmi.

Syncerus caffer emulates C. mearnsi in having conspicuously dark colouration. Instead of hiding from predators, it is adapted for gregariousness.

Mature males of P. leo - the only gregarious species of felid on Earth - have partly abandoned the crypsis required for stalking prey. Instead, the mane is conspicuously dark, for social/sexual reasons.

What this means is that, in a way, here we have an example of evolutionary convergence between a carnivore and two of its main species of prey. All three species feature conspicuous darkness in adaptation to gregariousness.

The THIRD photo (https://www.gettyimages.ie/detail/photo/two-lionesses-stalking-wildebeest-hiding-in-long-royalty-free-image/200134408-001?adppopup=true) further elucidates the same themes.

The species featured are C. mearnsi and P. leo. (Incidentally, the lone tree in the distance is Balanites aegyptiaca, featuring a browse-line at about 6 m high, formed by mature males of Giraffa tippelskirchi tippelskirchi.)

Even females of P. leo feature conspicuous darkness in a limited way, by possessing an auricular flag similar to that of A. jubatus. This allows members of the group to keep track of each other in cooperative hunting.

The FOURTH photo (https://www.grida.no/resources/2523), still in the Serengeti ecosystem, extends the themes to the world's largest bird.

The species featured are C. mearnsi (in the distance), the gazelle Nanger granti granti, and Struthio camelus massaicus - which functions ecologically much like this gazelle (https://www.africabib.org/rec.php?RID=Q00023835 and https://www.projecttopics.com/journals/bibliography/is-the-diet-of-the-ostrich-similar-to-that-of-grants-gazelle/).

Nanger g. granti, like E. t. nasalis, is adaptively conspicuous by virtue of the dark/pale contrast of banding on the flanks (extended to the hindquarters).

In the case of S. c. massaicus, the group shown is of adolescents - the offspring of several parents. When at the infant and juvenile stages, S. camelus has inconspicuous colouration, comparable with that of A. jubatus. However, this turns to conspicuous darkness in adulthood, particularly in males

The FIFTH photo (https://www.dreamstime.com/beautiful-ostrich-hot-africa-nearby-antelopes-here-photo-see-large-near-image168526517) shifts the scene from the Serengeti ecosystem to Etosha National Park.

The species featured are Struthio camelus australis and the gazelle Antidorcas marsupialis hofmeyri.

In adults of S. camelus, the sexes are similar in body size (https://www.alamy.com/stock-photo-couple-of-ostriches-struthio-camelus-at-the-bontebok-national-park-38030262.html?imageid=690B1C13-38B8-499D-B4EF-C1D03840B264&p=60598&pn=4&searchId=dca6a568865628209af3d56514ac1f36&searchtype=0). However, males are so dark that they are conspicuous when viewed solitary in savanna or treeless vegetation.

As in P. leo, the benefits of masculine advertisement outweigh the benefits of hiding, for this bird.

The link to gregariousness is more subtle than in the case of the mammals shown above. This is because males of S. camelus show paternal care to an extent and degree unknown in ungulates: they help to lead and guard groups of infants and juveniles that often coalesce the offspring of other parental couples.

In the case of A. m. hofmeyri, the conspicuous pattern is basically similar to that in the gazelles shown above. As in N. g. granti, the flank-band is not black, but achieves dark/pale contrast by virtue of the white on the flanks and rump, which extends high enough to catch the sunlight.

Posted on 10 April, 2023 03:46 by milewski milewski

Comments

thanks for your interesting articles

Posted by botswanabugs 10 months ago

@botswanabugs

Again, you're most welcome...

Posted by milewski 10 months ago

Add a Comment

Sign In or Sign Up to add comments