The same principles likely hold true for other predators, he said.
"All animals evolve ways to sense predation risk and avoid it, from the (single-cell) paramecium to elephants," he said.
Earlier studies documented sharp declines in two other daphnia species after the spiny water flea arrived in the Great Lakes in the 1980s, said David Bunnell, a fisheries biologist with the U.S. Geological Survey's Great Lakes Science Center.
But those studies presumed the only reason was that the water flea was eating daphnia, Bunnell said. The Michigan State team's findings offer an additional explanation: a slower growth rate.
"Certainly the hypothesis makes sense," he said.
Still, Bunnell said there had been no apparent reduction in the type of daphnia that Peacor's group observed. If that happened, it could affect the lakes' food web. The daphnia provides crucial nourishment for juvenile fish such as alewives and smelt that, in turn, are eaten by larger sport fish.
Todd Atwood, a research biologist with the Arizona Game and Fish Department, said the Peacor team's findings about damaging effects from avoiding predators offered insights for his studies of interactions between wolves, cougars and their prey in the West.
When wolves return to an area where they've long been absent, elk spend less time in open spaces — where they're easier targets — and more in places with heavier tree growth.
But that leaves the elk less time to forage. And it boosts their exposure to another predator: cougars.
