Ecosystem Scaling

Why aren't there more lions?

Until now, the assumption has been that when there is a lot more prey, you’d expect correspondingly more predators. But as we look at the numbers, we discover instead, that in the lushest ecosystems, no matter where they are in the world, the ratio of predators to their prey is greatly reduced. This is because with greater crowding, prey species have fewer offspring for every individual. In effect, the prey’s rates of reproduction are limited, which limits the abundance of predators.

Across many different ecosystems, from the Indian Ocean, the Canadian Arctic and the tropical rainforests, we find a surprising consistency in the relation of predators to prey, and confirmation that rather than the numbers of predators increasing to match the available prey, predator populations are limited by the rate at which prey reproduce.

The discovery of ecosystem-level scaling laws is particularly exciting. Their most intriguing aspect is that they recur across levels of organization, from individuals to ecosystems, and yet ecosystem-level scaling laws cannot be explained by their individual-level counterparts. It seems that some basic processes re-emerge across levels of organization, but we do not yet fully understand which ones and why.
(Photo credit: Amaury Laport)