You have to kind of look at the situation and try to pick the best method and one that you can go out and maybe validate on the ground by seeing if there are bears in those areas. In fact, there are Grizzly Bears living here in the Gravelly Mountains; a few bears here. There are a few here in the Tobacco Roots. Bears used to live up here in the Big Belt Mountains back in the sixties. Bears occasionally wander out of the Bob Marshall Wilderness and get about as far as Interstate 15. Since they began radio-tagging bears in these ecosystems, no bear has ever gone between any of these major ecosystems, even though it's within their dispersal distance. That doesn't mean that they won't, it just might mean that there are too many barriers at the moment. It also might mean that there's not enough population pressure, the habitat that they're in is not saturated and they don't need to leave.

We also looked at this using the same data with a different model.This was a Monte Carlo simulation model, developed by Douglas Williams from a basic algorithm of Michael Gilpinšs, which basically tried to simulate the way a bear might make choices from one pixel to another in a more random fashion. So, it's kind of difficult to see this but if a bear started down here in Yellowstone (and these bears were colored red) he'd wander back and forth through the mosaic of habitat, picking areas of good habitat. They would get about as far as this red area out here. If we started a bear in the green area, he might get out as far as this. A "blue" bear might get down this way. These purple areas are areas where "red" and "blue" bears would overlap.

This model may be a little bit more realistic in terms of the way an animal moves through the landscape. One thing it does do, though, is it kind of picks out some of the bottlenecks where there's very little habitat and it would be difficult for animals to cross. As you imagine these animals moving across the landscape, I'll just briefly talk a little bit about dispersal.

Narrative Index

Table of Contents

BioForum Index

AE Partners Collection Index

Activities Exchange Index