EPOW - Ecology Picture of the Week

Skin Patterns

African Elephant (Loxodonta africana)
Giraffe (Giraffa camelopardalis)
Burchell's Zebra (Equus burchellii)
Nile Crocodile (Crocodylus niloticus)

African elephants, like their Asian elephant cousins, have nearly naked skin except for scattered bristles and sensory hairs.  The skin is thick and leathery, and able to withstand extreme conditions of water and dry hot sun.  The modern elephant, in fact, evolved in Africa, shifting from very wet marshlands to drier, open environments.  Their thick skin has only rudimentary pigmentation of melanin varying from dense black to pale gray, brown, or rarely sensitive unpigmented pink.

Giraffes vary in the patterns and colors of the patches on their hide, the exact pattern being unique in each animal like giant fingerprints.  Of the 8 races of giraffe, the reticulated race reticulata of north Kenya is the most distinctive, with thin lines separating the dark patches, and the Masai giraffe race tippelskirchi of East Africa has the most irregular pattern.  The patterns likely help to camouflage the animals from predators such as lions.  Despite their size, giraffes become surprisingly difficult to spot when they step behind Acacia and Combretum trees on which they feed.

Zebras have a background of white to buff, with dark stripes that vary geographically and individually (again like fingerprints), being most complete and bold in the equatorial boehmi race.  In southern Africa, the antiquorum and burchelli races lack stripes on the lower legs and belly, and have shadow stripes between the black torso stripes.  The stripes, which seem bilaterally symmetric (mirror images on each side),  help to hide the animals in woodland thickets with broken sunlight, or in thick tall grasses.   One theory why zebras are black and white instead of investing in the extra energy to produce colored stripes, is because its primary predator, the lion, is  color-blind.   Rudimentary striping camouflage can be found in other ungulate species.  

Nile crocodiles are armored with large scales, like all reptiles.  Their coloration helps them blend into murky river waters and pools, where only a snout or eyes may show, as they await their prey in ambush.  

These four species illustrate how skin patterns have evolved according to where an animal lives, what it eats, what eats it, and probably the need to be recognized individually.  These are  ecological relations that would be impossible to learn in captive or zoo populations ... one has to observe the animal in its selected, native habitat in the wild to understand why it appears as it does.

Source:  
     Estes, R. D. 1999. The safari companion: a guide to watching African mammals. Chelsea Green Publishing Co., White River Junction, VT. 459 pp.
     Kingdon, J. 1997. The Kingdon field guide to African mammals. Academic Press, San Diego. 464 pp.

New information:
     Caro, T. 2005. The adaptive significance of coloration in mammals. BioScience 55(2):125-136.