A first theory on the adaptive colouration of giraffes, part 2

(writing in progress)

For the purposes of this theory I assume that there are three species of giraffes, namely a nothern/western one (Giraffa camelopardalis), a northeastern one (Giraffa reticulata), and an eastern/southern one (Giraffa tippelskirchi/giraffa).

I have chosen the following photos to show these at their most different:

camelopardalis

https://www.alamy.com/west-african-giraffe-niger-giraffe-nigerian-giraffe-giraffa-camelopardalis-image63628486.html

reticulata

https://www.dreamstime.com/reticulated-giraffe-samburu-national-reserve-feeding-kenya-image182437028

giraffa

https://www.dreamstime.com/giraffe-giraffa-camelopardalis-plains-etosha-national-park-namibia-giraffe-etosha-plains-namibia-image121771757

These species differ so much in colouration that one can generalise explanations to giraffes only in the case of certain minor features shared by them all, e.g. the tail and the ear pinnae.

It seems obvious that the spotting/blotching of giraffes reduces their conspicuousness to predators, by means of disrupting the outline of the figure. However, various caveats deserve explanation and some of them, in certain subspecies, are important enough to challenge this explanation categorically.

In approximate order of importance, the caveats include:

  • many individuals of Giraffa camelopardalis peralta are so pallid, owing to the predominance of the pale matrix over the spotting/blotching, that camouflage is an unconvincing explanation for this subspecies at any scale, distance, or illumination,
  • the form of the spotting/blotching varies so much among the species of giraffes that categorically different patterns occur in e.g. Giraffa reticulata vs e.g. Giraffa giraffa,
  • although giraffes do remain stationary at times when alarmed, they tend to give themselves away by peering over the tops of tall shrubs/short trees,
  • no comparably large-bodied mammals feature spotting/blotching,
  • the tail, when swished vs insects, is conspicuous enough to draw attention - at least by day - in situations where the animals might otherwise be overlooked,
  • all three species occur partly in vegetation so open that the whole notion of camouflage-colouration seems inappropriate.

In reticulata, the spotting/blotching is so modified that has become a different pattern, i.e. a network of pale superimposed on a darker 'matrix'. What is matrix in camelopardalis has become non-matrix in reticulata. These patterns cannot simply be equated.

Giraffa reticulata is ostensibly the simplest species to analyse, because:

  • it lacks subspecies,
  • its pattern is the most uniform of all the species/subspecies of giraffe, and
  • it lacks all conspicuous features other than the black tail-tassel and the pale posterior surface of the ear pinnae.

However, two basic problems remain in reticulata, making an overall function of camouflage unconvincing:

  • the network effect is too different from spotting/blotching to e assumed to function similarly, and
  • its habitat includes such low, open vegetation that it is difficult to portray it as being able to hide by means of camouflage.

to be continued...

(writing in progress)

Publicado por milewski milewski, 08 de diciembre de 2021

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