Where rates of predation by marbled salamanders were the highest, the spotted salamander larvae foraged more actively and showed faster growth.
Urban also collected salamander eggs from populations exposed to different degrees of predation risk and raised the larvae under uniform conditions.
Larvae that hatched from eggs taken from high-risk populations foraged more actively than those from low-risk populations, even when exposure to predators was held constant.
This showed that the risk-taking behavior is genetically controlled and has evolved independently in separate salamander populations, Urban said.
(Read related story: "Evolution's 'Driving Force' Shifts Based on Behavior, Study Says" [November 16, 2006].)
"Different feeding rates have evolved across a landscape of ponds separated by as little as 100 meters [328 feet]," Urban said.
The new findings make sense but also come as a surprise, said Andrew Hendry, a biologist at McGill University in Montreal.
"Here is one of those exciting moments in science when data overturn a seemingly inevitable and obvious generality," Hendry said.
"Prey that evolve with predators should evolve greater caution when foraging, right? Wrong—at least in Urban's system.
"The explanation for this inversion is itself obvious in retrospect," he continued.
"If predators can only eat smaller individuals, then prey should grow as quickly as possible."
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