“When predators help prey adapt and persist in a changing environment”

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Matthew M. Osmond, Sarah P. Otto, and Christopher A. Klausmeier

Predators can help prey persist in a changing world by increasing selection or decreasing generation times

Two ways predators can help their prey adapt, and thereby persist, in an ever-changing environment: the selective push and the evolutionary hydra effect

Phantom midge larva (Chaoborus americanus) are voracious predators of freshwater herbivores worldwide. In this issue, Osmond et al. show two ways in which predators can help their prey adapt and persist in a changing environment.
(Credit: Michelle Tseng)

According to the Oxford English Dictionary, a predator is “a ruthlessly exploitative or rapacious individual”. One would thus expect predators to hasten the demise of prey at risk of extinction. Indeed, many studies show that predators reduce prey numbers and it has also been shown that this can translate into prey extinction.

But are predators always bad for prey? To address this question, researchers from the University of British Columbia and Michigan State University built and analyzed mathematical models describing prey population dynamics and trait evolution in the face of a changing environment, with and without an interacting predator. The authors find two circumstances under which predators actually help prey adapt and persist.

The first mechanism occurs when predators kill more prey of a particular type, for example the sick and weak or the large and tasty, and this drives the prey to evolve in ways that are favoured in the new environment. That is, predators impose a “selective push” that helps the prey keep up with the environmental change.

This makes sense, but the authors find another circumstance where predators help, which occurs even when predators do not directly induce selection on their prey but simply eat them. By eating prey, predators free-up resources that allow prey to give birth sooner, reducing generation times and hastening evolution. Metaphorically, the predator acts like Heracles beheading the Hydra, except the multitude of heads growing back tend to be better adapted to the current conditions.

Matt Osmond, the lead author, points out that these findings “raise concerns for the conservation practice of removing predators for threatened populations, like Canada’s woodland caribou. While this practice may help prey survive in the short run, its unclear what effect this will have on their ability to adapt and persist in a changing world.” Read the Article