Fear really can kill

By Beth Daley, Globe Staff

Fear has its roots in survival. Being afraid enough to avoid the path of say, a grizzly bear, saves a lot of lives – particular if you imagine what would happen if you went up to one, looked it in the eye and tried to shake its paw.

But a University of Rhode Island ecologist says being afraid can have the unintended consequence of killing too.

Grasshoppers fear the wolf spider (Globe photo)

Assistant Professor Evan Preisser said that fear of being eaten can reduce populations as much or even more than the numbers of individuals being killed by predators. That’s because to avoid being eaten, many species will spend a lot more time hiding and less time eating. This can lead to a lower body mass, reduced reproduction rates, fewer offspring, and a lower rate of survival.

For example, fire ants – those swarming nasty-biting insects - are “totally freaked out” by a species of parasitoid fly that lays its eggs inside the ants, ultimately killing them.

“If one of these flies comes along, all the ants will hide and remain hidden for a really long time,” Preisser said. “Research by Donald Feener at the University of Utah has shown that the flies actually have a very low success rate at killing the ants because the ants are so good at hiding. They spend so much time in hiding, however, that the whole ant population becomes weaker.”

And fire ants fear a fly (Globe photo)

Other research conducted by Oswald Schmitz at Yale University shows that grasshoppers can be so afraid of wolf spiders that they will starve to death rather than come out of hiding and feed in the presence of the spider.

In a research paper published in the journal PLoS ONE in June, Preisser and Daniel Bolnick of the University of Texas-Austin found that the presence of a predator reduces some species' feeding and overall activity rates 57 percent and 45 percent among some species living in aquatic environments and by 45 percent and 34 percent among species on land.

“Just the simple presence of a predator can increase the mortality of prey species by as much as five percent,” Preisser said.

The URI ecologist is the guest editor of an upcoming special, three-article feature on “nonconsumptive predator effects on prey dynamics” in the September issue of Ecology, the journal of the Ecological Society of America.