Two identical terrariums, and in each of these terrariums, you have the rare and beautiful geosite daisy that is so endangered, and it's such a great thing to have. And all the people come from around to look at them. The difference is in the upper terrarium, it is divided into two by an unbreachable purple glass wall. Now, what's going to happen?
Well, as you might imagine, things are not perfect in terrarium land, and the blight comes. And the blight kills off one of your geosite daisies in each of the terrariums. But if you're down here, you're not worried, because you can grow this beautiful daisy, and it will grow back.
And it has its poesy, and it just gets grown back when, oh my goodness, the rust comes, and it wipes out one of the daisies in each of the terrariums. And if you're down below, you're still not worried, because it can grow back. And pretty soon, you have a beautiful display. But if you're up above, you're really worried, because now you're extinct.
Now, suppose that instead of this being worried geosite daisies in our terrariums that we were worried about Glacier National Park seen in a map and Yellowstone National Park seen in a map down here. And at the present time, Glacier and Yellowstone are connected by corridors that are essentially wilderness running down the Rocky Mountains.
What is going to happen if we lose those corridors of wilderness that connect the two and turn them into islands? And the simple answer is you don't lose everything, but you probably do lose some of the things that live in both of the parks, just as for the terrariums you get extinction.