I've always thought that the lack of contiguous habitat has adverse effects on the critters and plants that can live there, and this study is one of the more recent that verifies that intuitive thought:
The new study, led by Nick Haddad, a professor at North Carolina State University, and co-authored by Laurance and others, found that fragmented habitats lose an average of half of their plant and animal species within twenty years, and that some continue to lose species for thirty years or more. In all of the cases examined, the worst losses occurred in the smallest habitat patches and closest to a habitat edge. The study also demonstrates, using a high-resolution map of global tree cover, that more than seventy per cent of the world’s forest now lies within one kilometre of such an edge. “There are really only two big patches of intact forest left on Earth—the Amazon and the Congo—and they shine out like eyes from the center of the map,” Haddad said.
Think about that and treasure those times when your running habitat more closely resembles the primeval forest.