Fear of predators, like the lynx pictured here, can have a serious impact on populations of prey animals. Photo credit: Remarkable Rabbits Inc
Removing predators from an environment altogether could be a better way of studying the impact that fear of predators has on prey populations, says a new study by UAlberta biologists.
In the last decade, biologists have discovered that the population effect of predators on prey animals is more than just the ones that are killed and eaten. Rather, cues in the environment alone, like predator calls or urine, are enough to affect prey populations.
"It can be that based on these environmental cues, prey avoid certain areas altogether, causing reduced foraging and higher stress," explained Michael Peers, PhD student in the Department of Biological Sciences. "All of these factors can have downstream effects on reproduction or even starvation. This effect could rival the effect of prey actually being killed by predators."
Despite a common acceptance of potentially large fear effects, a new study led by Peers suggests the way researchers currently measure predator fear likely exaggerates its effect on prey populations. In the paper, Peers outlines an alternative model for measuring the predator fear effect.
"Most studies are predator-cue experiments, where scientists distribute cues of a predator-like urine or playing animals calls-onto a landscape and then study the prey's response," said Peers whose research is supervised by Professor Stan Boutin. "The challenge is that researchers tend to use overblown cue intensity, using overwhelming cues that are not representative of actual predator activity, resulting in an exaggerated effect in prey animals."
New approach
The new paper offers an alternative approach, suggesting that instead of mimicking predators to increase predator fear, researchers remove predators altogether and mimic consumption by taking prey out of the system. In other words, researchers would remove all predators, and then then simulate the killing effect of the predators by trapping and removing some prey animals from the environment on a regular basis.
"If you remove predators and therefore the fear, the difference between the study population and the natural population is the fear effect," explained Peers. "So, if a prey animal's reproduction is limited by fear in the wild, removing fear should cause an improvement in reproduction."
The proposed method would eliminate the exaggerated effects simulated in cue-based studies, providing more accurate information for wildlife managers and giving scientists new, more accurate insight into the factors affecting prey demography.
The paper, "Quantifying fear effects on prey demography in nature," is published in Ecology (doi: 10.1002/ecy.2381).