By Chris Doughty, University of Oxford
As recently as 12,000 years ago, much of the world looked like an African savanna. South America teemed with large animals which overlapped with stone age humans, including several species of elephant-like creatures, giant ground sloths, and armadillo-like creatures the size of a small car.
Skeleton of Megatherium, the giant tree sloth. Image: Ballista
In South America, most nutrients originate in the Andes mountain range and are washed into the forests through the river system. However, on dry land, these nutrients are in short supply unless they are transported by animals in their bodies and deposited in their dung. While small animals distribute nutrients over small distances, large animals have a much greater range. For instance, big animals have larger home ranges than small animals, they eat more, and they have longer guts. When these large animals became extinct, their habitat lost not only them but the nutrients they moved.
With colleagues, I developed a mathematical model, similar to one used by physicists to calculate the diffusion of heat, to estimate the ability of animals to distribute nutrients. The model is based on the body size of the animal, drawing on existing data of their fossilized remains. From this, we can estimate how much the animals ate, defecated, and the range and distance they travelled.
People add nutrients to the planet by using fertiliser in agriculture. However, while large animals tend to distribute nutrients, we tend to concentrate them. Large animals such as cattle are now fenced and unable to spread nutrients around the way free-ranging creatures once did. So today, certain areas have too many nutrients (areas near agriculture) and other areas too few (natural ecosystems).
This article was originally published at The Conversation. Read the original article.
