|Assorted browsers and browse lines, Selous GR, June 2010|
|Giraffe (and shorter!) browse line, Arusha NP, June 2010|
|Greater Kudu, carefully nibbling around thorns, Kruger NP, May 2011.|
Of course there might also be heritable variation in the impala browsing technique or mouths - maybe for thicker skin, or a narrower nose that can squeeze between the thorns. Giraffe, of course, have evolved a huge long sticky tongue so they practically lick the leave out from between the thorns, rather than have to go to close. But both species certainly are aware of the thorns, even though they have no choice but to eat the prickly trees, of course - imagine what would happen to the poor thorn tree that, though some mutation, had no thorns. Ooops, poor thing! So clearly the thorns do have an impact - what's interesting to me to look for in places with very heavy browsing is evidence that the thorns do work, even though the plants get eaten.
|Heavily browsed yellow-barked Acacia, Arusha NP, June 2010|
To see this, you need to look at the shapes of trees and bushes. Here's a nice Vachellia xanthophloea (see, I'm trying to get you used to the new names!) that's been very hevily pruned - a favourite with the girafe. So how's it ever going to make the leap from heavily pruned bush to fully fledged tree? The secret is to grow wide, before growing tall. While the bush is still short and relatively narrow it doesn't stand a chance - any giraffe will bend down, and chew off the top bits. But if it can get wide enough the giraffe don't like the thorns on their skin, and they'll just nibble to top bits within easy reach - leaving a tuft in the centre to break away. And once that is done, those short, wide branches at the base of the tree are no longer important and soon die back, in favour of the taller tree. Not clear? She here's a little diagram showing how to escape giraffe broswing pressure...
|Bushes escaping browsing. Honest!|
|Nearly there! This bush behing the giraffe has started to escpe from the centre, Lake Manyara NP, April 2010|
|Made it! Just a few whisps of short left, West Kili, April 2010|
And that, for now, is that. Hope you're having as much fun as I will be having in Mwiba!