Science magazine had an article exploring a paradoxical observation: acacia trees fenced off and protected from herbivores seem to be less healthy. It turns out the acacia trees are usually in a symbiotic relationship with a species of ant that protects them. When nobody’s munching on the trees, they stop providing for the ants and the symbiotic relationship breaks down — in a way that’s actually worse, in the end, for the acacia.
Then I started wondering, tangentially, if giraffes and acacias coevolved tallness. So I googled around… what I actually found was some surprising controversy regarding the evolution of the giraffe’s neck.
Everyone pretty much assumed they evolved tall necks to reach more leaves, but in 1996 a couple of guys proposed that the neck was actually a product of sexual selection. Turns out that the males use their necks as weapons when fighting each other. Check out this crazy youtube video. (url: http://www.youtube.com/watch?v=C7HCIGFdBt8 )
The argument they had against the feeding hypothesis was that giraffes spend a lot of time browsing at or below shoulder level. In 2007 another group published a study which found that higher quality biomass was available to giraffes higher up, due to competition with other foragers at lower levels. In the end I think I’ll stick with the tall-to-reach-leaves-hypothesis, but I thought this video of fighting giraffes was too awesome not to share.