Predators are dark-spotted but their ungulate prey are pale-spotted. Why?

Spotting is a form of camouflage for both predators and their prey. However, what remains to be explained is why the the pattern is inverted in the two categories in mammals.

The spots of cats (Felidae, see https://en.wikipedia.org/wiki/Serval), hyenas (Hyaenidae, see https://www.torontozoo.com/animals/Spotted%20hyena), civets (Viverridae, see https://www.zootierliste.de/en/?klasse=1&ordnung=115&familie=11503&art=50901342) and other Carnivora are dark against a relatively pale ground-colour. By contrast, the spots of deer (Cervidae, see https://commons.wikimedia.org/wiki/File:Spotted_deer_(Axis_axis)_male.jpg), tragelaphin Bovidae (see https://sorryoutofoffice.files.wordpress.com/2013/10/p1150963.jpg) and certain relatively large Neotropical rodents (see https://en.wikipedia.org/wiki/Paca) are pale against a relatively dark background.

One way to approach this puzzle is to examine any exceptions, but this turns out not to be particularly enlightening.

In the case of Carnivora, I cannot think of any real exceptions. Broadening the search, an exception can be found in an Australian carnivorous marsupial. The spotted-tailed quoll (Dasyurus maculatus) certainly has pale spots on a relatively dark background (see https://wildlife.org.au/spotted-tailed-quoll/).

In the case of ungulates, an obvious exception is giraffes (Giraffa, see https://www.flickr.com/photos/isaacpacheco/14402047495). However, these are also by far the largest land-animals with camouflage colouration, complicating any comparisons. Why giraffes are spotted in the first place is a question unto itself.

One reason why the nearly categorical difference between predators and prey is surprising is that all of the spotted Carnivora are themselves vulnerable to their largest local relatives. The lion (Panthera leo), after all, readily kills all other Carnivora regardless of whether it finds them acceptable as food. This makes it hard to know whether the spotting of the cheetah (Acinonyx jubatus), for example, serves more to hide it from its prey, or from its own predators, namely the lion, the leopard (Panthera pardus) and the spotted hyena (Crocuta crocuta). Even in the case of the spotted hyena, second only to the lion in the African hierarchy, the spotting is puzzling because this species hunts by pursuit to the apparent exclusion of camouflage-dependent stalking.

Any naturalist who has spent time pondering adaptive colouration will know how enigmatic this field of biology can be. The patterns of colouration in animals seem to defy generalisation and prediction, discouraging further enquiry. However, in the riddle of the dark-spotted predators versus the pale-spotted prey we at least have an unusually clear-cut question. Are we up to the challenge of solving at least this major puzzle?

Publicado por milewski milewski, 29 de abril de 2021

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