The study examined differences in the hoarding behavior of red squirrels and gray squirrels in west-central Indiana. The researchers used that information to develop a model that predicts how these differences may influence germination, or sprouting, of black walnut trees, a major component of the central hardwoods forest and the food of choice for both species.
"This is the first study I'm aware of that's explicitly looked at how two different species and their behavioral characteristics could influence forest regeneration," said Rob Swihart, professor of wildlife ecology.
In the study, Swihart and his colleague Jake Goheen, a former Purdue student now at the University of New Mexico, predicted that seven times as many walnuts germinate when gathered by gray squirrels compared to those hoarded by red squirrels.
"If our results are widely applicable, the processes by which trees propagate will be significantly altered as more red squirrels move into the landscape," Goheen said.
Unlike gray squirrels, red squirrels are not native to Indiana and only began to spread throughout the state within about the past century. At the same time, the number of gray squirrels in forests began to decline as more forest habitat was converted for agriculture, he said.
The problem with this shift in species is that gray squirrels and red squirrels don't store nuts and seeds in the same way, and they play different roles in the forest community, Goheen said.
Gray squirrels use what ecologists call "scatter hoarding," in which they bury single nuts, such as acorns and walnuts, in numerous locations.