Until recently, many ecologists didn’t study the effect of evolution on population dynamics because evolution is much slower than the predator-prey cycle. But a study suggests that adaptive evolution might actually play a role in the dynamics of the predator-prey relationship.
Cornell University biologists studied the population dynamics of green algae and rotifers, the microscopic aquatic animals that feed on them. They expected that the rotifers would eat the algae and multiply until the algae population crashed. This would then cause the rotifer population to crash, which would allow the algae population to recover, and the whole cycle to begin again.
What they observed, however, was that there was some lag between the time the algae population reached a certain density and the time the rotifer population began its recovery. Why? And how does evolution fit into all this?
Well, it turns that some algal cells are resistant to digestion, although this resistance comes at a cost: they reproduce more slowly. As the more dominant, non-resistant strains of algae crashed, the resistant algal cells began cloning themselves more rapidly, and this temporarily stabilized the algae population.
In the meantime, the rotifer population crashed because the rotifers had less to eat, allowing the non-resistant strains of algae to recover. Once the non-resistant algae became common again, the rotifer population increased, completing the cycle. So basically, adaptive evolution enabled the algae population to reestablish itself by delaying the time it took the predator population to recover.
Understanding the effects of adaptive evolution may help scientists to better understand the behavior of drug-resistant bacteria and outbreaks of disease.