Giraffes versus acacias

As animals have evolved to secure advantages in the constant battle for species survival, so have other animals and plants evolved to defend themselves and win their own battles. A good example of punch and counterpunch, in evolutionary terms, is that of the giraffe and the acacia.

Rounds one and two

As everyone knows, the giraffe is a species of antelope that has gone for tallness in a bid to reach food sources that are not available to other grazing animals. A particular favourite is the acacia tree, which is normally safe from other animals because of its thorny leaves. However, the giraffe’s long neck has a joint at the top that enables the head to point straight up, and its tongue is more than 20 inches long. This means that giraffes can get access to the very top of many acacias, and it is at the top that the fresh young leaves grow that have not yet developed their thorns.

If round one went to the acacias, by keeping the thornless leaves out of harm’s way, then round two seems to have been won by the giraffes. What about round three?

Round three

The fightback by the acacia has been the ability to make the young leaves taste bitter for a short time. They do this by releasing a chemical that only has this effect when the tree is “under attack”, and this chemical can be borne on the wind and carried to other acacia trees as a sort of warning to them to do the same. The giraffes might therefore find that their tasty meal is not so tasty after all.

Round four

And for round four? The giraffes have sussed out the acacias’ trick and always approach the trees upwind, so that the warning signals will be blown in the wrong direction from the trees’ point of view and the giraffes will therefore have a chance of munching a good few mouthfuls of leaves before the tree has a chance to turn its “yuck factory” on.

What will happen next?

If the balance is maintained such that giraffes and acacias can both thrive as things are, then there may be no need for a round five. However, should conditions change to their disadvantage, it looks as though it is up to the acacias to develop the next tactic!

© John Welford