The Ripple Effect
You might ask yourself – how could the wolf population in Yellowstone National Park effect the cottonwood tree population? There is, in fact, a close tie between these seemingly opposite objects – in order for the cottonwoods to flourish, the wolves must be present.
In mid-January, 1995, fourteen captured wolves from Canada were brought to Yellowstone National Park. This was the first time in nearly 70 years that a wolf had stepped paw into the park. The reintroduction of the wolves was crucial to saving the cottonwood trees.
Before the reintroduction of the wolves, researchers began to notice that there was a significant decrease in the cottonwood tree population. For some reason, there were no new cottonwoods growing; there seemed to be only old cottonwoods left. Researchers were puzzled – they couldn’t understand how cottonwood trees weren’t growing in a place that had very little human interference. But then they figured it out – the problem was elk.
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Researchers continuously found tons of cottonwood seedlings. At first they were hopeful, but shortly after, they were puzzled. They expected to see many young cottonwood trees, but none were growing. Finally they figured it out – the elk were eating all of the seedlings causing no new cottonwoods grow.
This is what happens when there is a removal of a top predator, in this case the wolf. The wolf’s prey, which is the elk, is not threatened anymore when the wolf is removed. The elk are free to reproduce and grow in population without the fear of having to run for thier lives from the wolves. This causes an overpopulation of elk. Because there are more elks, the population needs more food. Before, when there were wolves, the elk would munch on cottonwood seedlings, but there were never enough elk to be able to eat almost all of the seedlings. After the last wolf died in Yellowstone, the elk population boomed, and there were enough elk alive to be able to wipe out almost all of the cottonwood seedlings.
With the reintroduction of the top predator, the elk population has gone down in size, and cottonwood trees are now beginning to grow again.
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So why should we care about the removal of a top predator? The fact is, this is a common issue in many communities. In Illinois, many people are experiencing the overpopulation of deer. Because Illinois has killed many of its top predators like bears and coyotes, there has been an overpopulation of deer. Many deer do not get enough to eat – some could end up in your backyard munching on your vegetation. Also, the places where deer can live are becoming smaller and smaller. This causes deer to stray from their natural habitats into backyards, parks, and roads. Many people ruin their cars from hitting deers.
Because the top predator has been removed – people have to create a human-made ecosystem service. Instead of letting bears and coyotes take care of the deer population, humans have wiped out these main predators and have had to replace it with a costly service – hunting. So instead of using a free service (top predator population control), people now have to spend money to take care of it themselves. By doing this, humans are also greatly reducing the bear and coyote populations.
So we should remember that the removal of one plant or animal can greatly effect the environment they are taken out of. Two totally unrelated things could actually be inadvertently related, and it is important that we really study this before removing things from our own communities.
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