FOOD CHAINS

We’ve all been taught about food chains in high school biology and it’s always represented in a very simple diagram. Plants get food from the sun. Cows eat plants. People eat cows, that sort of thing. I think we really take for granted just how complex the food chain is and the importance of the interdependence of species. Zoologist Todd Palmer and his colleagues have been studying the interdependence of species in Africa focusing on the Acacia tree, ants and herbivores. The acacia tree is the most common shrub of the savanna and despite the long thorns provides sustenance to animals like elephants, giraffes and zebras. The acacia tree has struck up a sort of bargain with a certain species of ant who build their homes in the hollowed out thorns of the tree. In return for a place to live and some food the ants defend the tree from really intrusive herbivores.

This is where it gets complicated. If there are no elephants or giraffes nibbling on the tree, the acacia stops producing the little ant houses and excreting the sweet nectar that the ants eat. By spurring more growth, the acacia tree becomes a home to another type of ant. These new ants, Crematogaster sjostedti, are not nice ants. They don’t defend the tree at all. In fact they depend on bark-boring beetle larvae to build their homes. This causes the tree to die twice as often then when they are regularly being chewed on.

So, simply put, tree needs good ants for defense against herbivores which it also needs to keep bad ants away. This is why every organism on this planet is important.