Edge shape, animal dispersal and habitat fragmentation.

Habitat fragmentation is one of the most important threats to species extinction, making it perhaps the most important contemporary conservation issue. Human development fragments natural habitats into patches - animals now need to cross dangerous habitat to travel from one patch to another. The kind of edge around habitat patches affects how easily animals do this and the stability of their populations hinges on how easily they can travel.

Conservation biologists till now have thought that the most important aspect of edges that affects animal travel is edge length - for example, if an animal is moving around inside of a patch, then the more often it encounters an edge, the more likely it is to cross the edge. Thus, the more tortuous the edges the greater the animal travel.

But in preliminary work I have discovered that some animals also respond to the shape of the edge. This is important because there are many different shapes of edges, even for the same edge length. For example, one way that edges vary is in the spatial scale of their tortuousity. Thus animal travel may be much greater or less than we previously thought, depending on the shapes of habitat edges. And, animals' population stability might be much greater or less than we thought.

I propose to find out what mechanisms animals use respond to edges, and how does this response depend on various aspects of edge shape - by a) the spatial scale of edge tortuosity, b) edge hardness, or width and c) particular shapes of edge geometries.

First, I will use computer simulations to develop specific predictions. Then I will test those predictions using lab experiments with beetles, field experiments with meadow voles, and movement data of wild mule deer and elk. The importance of the lab experiments is not that the beetles are themselves important, but because I can control the system and test specific factors. The importance of the meadow voles is that fragmentation has a great effect on their populations - and, because it is easy to carry out experiments in the wild. The importance of the deer and elk is that they are freely-living animals that I can study without any manipulations - the ultimate test of ideas about edges. This part will be a collaboration with a long-term study of deer and elk in Oregon, where biologists have tracked many individuals for many years. Thus I will have I have access to detailed data from movement patterns of elk and deer as well as digitized habitat maps.

Edge shape effects are important because they are felt both up and down the food chain. Here are three examples. First, many small mammals respond to edges, thus affecting the many predators that eat them. Second, some pollinating bee species avoid edges while foraging, thus affecting the flowering plants they are pollinating. Finally, many birds respond to edges while dispersing plants. Results from my research will show how all of these processes are affected by the shape of edges.