So here we have an example problem that says, in 1995, 15 Alberta gray wolves were introduced to Yellowstone National Park. Now their population has expanded to over 100 and they have brought about significant changes. They primarily prey on elk, so the elk population has remained stable since the wolves' introduction. The leftover elk carcasses provide food for ravens, eagles, and bears, and the reduction in elk numbers has allowed more vegetation growth, which provided habitats for birds and beavers, allowing their respective populations to grow. How would you describe Alberta gray wolves in Yellowstone National Park and why?
And we've got these 4 potential answer options down below. Now, clearly, these Alberta gray wolves are having a huge impact on their community as they are initiating all these different changes described here in this problem. Now these Alberta gray wolves are not physically changing their environment, so they're not going to be ecosystem engineers. So we can cross that off. Now, what we can see here is that, if we can eliminate answer option c, we can also eliminate answer option d, which says all of the above.
So now we're between either foundation species or keystone species. Now a foundation and keystone species are both going to have huge impacts on their communities. The difference is that a foundation species is going to have large biomass in the community, whereas keystone species are going to have relatively low biomass in the community. And so what we need to realize here is that only 15 Alberta gray wolves were initially introduced. That's not many at all in this Yellowstone National Park.
And their population only grew to over a 100, which still is not very many wolves. And so these wolves, despite having low biomass and low abundance in their communities, are having a huge impact on their community. And this is what makes these gray wolves a keystone species. So, option b is the correct answer, which says keystone species: they're not abundant, but their presence has a large impact on the community. And so b here is the correct answer to this example problem.
That concludes this example, and I'll see you all in our next video.