In nature, the relationship between predators and their prey seems like it should be simple: The more prey that’s available to be eaten, the more predators there should be to eat them.
If a prey population doubles, for instance, we would logically expect its predators to double too. But a new study, published Thursday in the journal Science, turns this idea on its head with a strange discovery: There aren’t as many predators in the world as we expect there to be. And scientists aren’t sure why.
By conducting an analysis of more than a thousand studies worldwide, researchers found a common theme in just about every ecosystem across the globe: Predators don’t increase in numbers at the same rate as their prey. In fact, the faster you add prey to an ecosystem, the slower predators’ numbers grow.
“When you double your prey, you also increase your predators, but not to the same extent,” says Ian Hatton, a biologist and the study’s lead author. “Instead they grow at a much diminished rate in comparison to prey.” This was true for large carnivores on the African savanna all the way down to the tiniest microbe-munching fish in the ocean.
Even more intriguing, the researchers noticed that the ratio of predators to prey in all of these ecosystems could be predicted by the same mathematical function — in other words, the way predator and prey numbers relate to each other is the same for different species all over the world.