UNIVERSITY PARK, Pa. — In the big woods of Pennsylvania's Northern Tier, the home range of the average white-tailed deer is more than twice as large as that of a deer in urban or agricultural areas of the state. Penn State researcher Duane Diefenbach documented that phenomenon early on in his work, but it did not occur to him it might be representative of many different mammal species around the globe.
The adjunct professor of wildlife ecology in the College of Agricultural Sciences, who focuses on management implications of his findings, never had an opportunity to ponder the bigger picture until German researchers invited him to contribute data to a worldwide study of mammal movement. Diefenbach has monitored the movement of dozens of deer fitted with global positioning system collars over the past five years as part of Penn State's Deer-Forest Study.
"In Pennsylvania, we can go from contiguous forests to highly fragmented landscapes that are dominated by agriculture with small wood lots, and I noticed that when we had highly fragmented landscapes, home ranges of deer were much smaller — and the deer we studied in contiguous forest and undisturbed areas had larger home ranges," said Diefenbach, director of the Pennsylvania Cooperative Fish and Wildlife Research Unit at the University.
"I attributed it to a couple of things. The fragmentation leads to many different types of plants available to deer so they do not have to travel as far in search of food. Also, people tend to live in areas with better-quality soil, because crops grow better, which also provides more food for deer."
Diefenbach's research has shown that in the big woods of Pennsylvania, the home range of male and female deer outside the breeding season is about a square mile. But in the agricultural areas, a deer's home range is more likely to be half of a square-mile or even a third of a square-mile. In the rut, males generally have twice the home-range size of females, he noted, but outside the breeding season they have essentially the same home-range size.
It turns out that Diefenbach's observations in Pennsylvania are identical to what wildlife researchers around the world have seen with other species. On average, mammals move distances two to three times shorter in human-modified landscapes than they do in the wild. These findings, produced by an international team of researchers, appear today (Jan. 26) in the journal Science.
This is the first time this topic has been examined at a global scale and for many different species at once. The authors suggest that these results may have far-reaching consequences for ecosystems and in turn, for society. Diefenbach is a co-author of the research.