Geology of the National Parks

Textbook 12.2: Yellowstone


Island Biogeography, Yellowstone and the Next Mass Extinction?

Mother grizzly bear and two cubs crossing the highway near Glacier National Park, Montana.
A mother grizzly bear and two cubs crossing the highway near Glacier National Park, Montana.
Credit: R.B. Alley

Most of the national parks were established to preserve geological features. A few parks, such as Sequoia and Redwood, were established for biological reasons. Increasingly, however, the national parks are visited, used, preserved, and managed for biodiversity. We humans continue to spread. More and more land is brought under cultivation. More of the produce of the sea is netted and served to humans. Some estimates are that we and our immediate friends—cats and corn and cows—now use about half of everything that the world makes available for us and everything else. And, with about 7 billion of us here now, heading for 9 or 10 billion, and with a couple of billion of us not using much but hoping to use more, all humans taken together may double what we're using. Ultimately, this leads to extinctions and loss of biodiversity.

Map of the US with Yellowstone National Park highlighted, primarily in Wyoming but extending slightly into Montana, and Idaho.
Credit: R.B. Alley

This is a geology class, and biodiversity is a bit far-afield, but we have time for a quick detour. We saw that there have been mass extinctions in the past—times when many living types became extinct in a short interval. There is a real chance that a geologist far in the future would place our current time as the latest mass extinction, the end of the Cenozoic, and the start of the Anthropocene.

Early humans were surprisingly hard on biodiversity. Wherever humans arrived with their efficient tool kits—in Australia, New Zealand, other islands, the Americas—extinctions of large animals followed. Direct human hunting, or competition from the rats, pigs, dogs and others that arrived with the humans, likely contributed.

Some people don’t like the idea that early humans were hard on biodiversity. Many people, including good scientists, have argued that the extinctions of large animals in the Americas were caused by climate change, which happened to occur at about the same time as human arrivals in some places. Dr. Alley has listened to talks in which data he helped produce were used to argue that the climate changes were so large and rapid that they must have been responsible. But, the work by Dr. Alley and others showed that dozens of such abrupt climate changes occurred, and the extinctions did not occur until the humans arrived. It is hard to imagine that a couple of dozen abrupt climate changes happened without killing off many species, and that just when fluted-point spears showed up in the rib-cages of mammoths, the next abrupt climate change was solely responsible for killing the mammoths, and humans did not play a role.

But, the earlier extinctions were mostly of large creatures. Since the industrial revolution, “modern” humans have contributed to extinctions of various creatures. And, the rate of extinction may pick up soon as we increasingly occupy the planet. To see why, let’s take a little detour into island biogeography.

Island Biogeography

If you were to visit a lot of islands that are more-or-less the same distance from the mainland, and count the number of species on each island and measure its area, you would find that the bigger islands have more species. Roughly, an island with ten times the area as another will have twice as many species. If you visited islands of about the same size at different distances from the mainland, you would find that those closer to the mainland have more species.

At least some of what controls these observations is not too difficult to understand. If you have a small island, it can hold only a few individuals of a species. From year to year, populations go up and down depending on food supply, predators, and other things. With a small population, a small drop can hit the absorbing boundary of zero individuals and cause extinction, but a large population can survive a small drop. So extinction is more likely on a smaller island, and smaller islands have fewer species. The mainland is there to supply new individuals to islands to replace those that die, and repopulation is easier for islands closer to the mainland, so those islands closer to the mainland have more species.

These patterns of island biogeography are well-established. Studies of repopulation of islands sterilized by volcanic explosions, and even of very tiny islands that were deliberately depopulated and then allowed to come “back to life,” have shown that this is the way the world works naturally.

Now, think about Yellowstone. Originally, the boundaries drawn for the park separated wilderness inside from wilderness outside. Today, as shown in the satellite photo, some of the park boundaries are easy to see from space because loggers outside the park work right up to the boundaries. Yellowstone remains connected to other wilderness regions in other directions; it is not an island (yet).

Landsat-7 image of mature forest in Yellowstone (right) beside logged forest in Targhee National Forest (left)
Landsat-7 image of mature forest in Yellowstone (right) beside logged forest (clearcuts in pink; two are indicated by pink arrows) in Targhee National Forest (left), Montana. North is toward the top. The blue arrow at the top points along the park boundary. It is easy to see many national-park boundaries on satellite images such as this one, because the extensive human modification of the land surface outside the park is evident next to the unmodified conditions in the park.

But what if Yellowstone were an “island,” as some other parks are or soon will be? Suppose a park becomes surrounded by farmland, which is used to feed humans and keep us alive. Farmland does not support a lot of wild orchids or wolves. Farmland is impoverished in biodiversity, with just a few species, carefully selected to feed us. A park surrounded by farmland is an island, because many species have great difficulty crossing the farmland just as many species have difficulty crossing the ocean. And, from the well-established principles of island biogeography, isolation of a parkland from other wilderness will cause extinctions in the park. Perhaps more worrisome, if the only remaining wilderness is in parks, there is no longer a “mainland” to replace species lost to local extinction on the island—extinction in the park is then extinction from the world.

We know that as climate changed in the past, plants and animals migrated long distances to stay with their preferred climate. As the climate changes in the future, migration will be required, but may be impossible if the parks become isolated.

So, Who Cares?

Mountain Goat
Mountain goat, Glacier National Park, Montana.
Credit: R.B. Alley

One can ask whether biodiversity is worth preserving. This is proving to be a difficult topic, and one that will be discussed much in the future. Certainly, many of our medicines have come from plants, and if many plants become extinct before we can study them carefully, we are likely to lose many possible medicines. Engineers and designers are increasingly using “biomimetic” techniques—mimicking nature. Evolution has worked over vast times to select the most successful biological patterns, and we can learn from them, if they are here to be learned from.

More-diverse ecosystems seem to be more productive (if you have hot-loving and cold-loving and wet-loving and dry-loving types in a region, then something will grow well no matter what weather arrives; if you have only one type, and the weather is bad, so is the crop), so if producing more is good, biodiversity seems good. But, the difference is not huge.

Living things have frequently served as “canaries in coal mines”. Miners would take a canary along in the mine, not only for companionship, but because the birds were more sensitive to bad air than were people, and a sick or dead bird would warn miners to get out before the miners became sick or dead. Birds of prey served that function for us with DDT. This chemical was going to free us of pests, increase crops, wipe out diseases—until the falcons, hawks, eagles and other predatory birds started disappearing. A little DDT on a plant led to more DDT in an insect that ate lots of plants, and still more DDT in a bird that ate a lot of those insects, and became so concentrated in a falcon that ate the birds that the falcon’s eggs broke and young ones couldn’t be raised. It became clear that such “bioconcentration” threatened us with problems as well—the other living things gave us a warning. Loss of biodiversity means loss of warning sensors.

And, many people like diversity (look at the money spent on zoos, and the interest in charismatic macrofauna in parks). Further, some people see a moral issue—do we really have the right to terminate the existence of other living things?

Some planners today are trying to establish corridors connecting wilderness areas, so that the parks do not become islands and lose species. How successful this plan will be remains to be seen. The “simple” answer is that, to maintain many species on Earth, we have to maintain much wilderness. And that in turn has implications for how we humans choose to behave.