Species Evolution Throws a Wrench into Predator-Prey Population Cycles with Weird Reversal

It turns out that evolution may have some interesting effects on predator-prey population cycles. Co-evolutionary changes in species may create the appearance that the pretty are actually eating the predators.

Predator and prey populations usually follow predictable cycles. When a prey population grows, predator populations also grow due to an increase in food. Yet when the predator population becomes too large, the prey population can plummet; this causes the predator population to also crash. Yet these cycles change when evolution is thrown into the mix.

When both species are evolving, the traditional cycle may reverse and the predator populations may peak before the prey populations. Why is this? That's a good question.

The scientists took a look at co-evolutionary changes by examining three predator-prey pairs-mink-muskrat, gyrfalcon-rock ptarmigan and phage-Vibrio cholerae. The scientists simulated models in which the evolutionary process was sped up to show how co-evolution would affect the population cycles.

"With predator and prey co-evolution, you can see oscillations in which there are lots of prey around even when there are many predators, or lots of predators around even when there are very few prey," said Michael Cortez, one of the researchers, in a news release. "When prey is abundant and there are few predators, it may be because there are lots of defended prey-prey that the predators can't eat. When there are lots of predators around and few prey, it's because the prey are very good food sources and the predators are doing quite well."

The findings reveal that evolution can throw a wrench into usual predator-prey cycles. This, in turn, could inform scientists' understanding of these interactions, which could be applicable to conservation efforts in the future.

"This study identifies how adaptation between two species and interactions between their numbers can result in something different from what you would get if you just had the interaction between the numbers," said Cortez in a news release. "This is something that will show up across many ecological systems. We can now explain broad trends that occur in vastly different systems using a theoretical approach, and the fact that we can identify the mechanism responsible for it is unique to our study."

The findings are published in the journal Proceedings of the National Academy of Sciences.