Many people do not know why wolves should be reintroduced back into the ecosystems of the continental U.S. and what change it will actually cause. However there are many reasons as to why wolves are such a necessary part of the ecosystem. The main reason for their reintroduction is because they keep elk and deer populations in check, which in turn aids plants and other animals. Before wolves were reintroduced elk and deer herds had over browsed streams and several other areas of Yellowstone and the surrounding states. This in turn led such plants as aspen, willow, and cottonwood to be unable to grow properly and become part of the canopy of the forests. Likewise, just like a domino affect, other wildlife such as songbirds and beavers were affected. This domino-like affect is what is known as a tri-trophic cascade.
A tri-trophic cascade involves the three trophics or levels of an ecosystem. You have your predators, prey, and plants; three levels of an ecosystem that all affect each other.And this is where the term cascade comes in. To best explain this, think of a waterfall. As the water falls off the cliff it splits off into two streams of water. Then those two streams split yet again, and then those split. This continues until you have dozens of streams all flowing down from the one river that led to a waterfall. This is very similar to how a tri-trophic cascade works in an ecosystem. Everything is connected from the very top to the very bottom. Likewise those in this ecosystem can be affected if one is not present. So without wolves, an apex predator, every other species from elk to aspens are affected. To give a greater illustration of this let’s go back to our waterfall example. If there was an avalanche and rocks obstructed parts of the waterfall, it would have to change how it flowed. So if a couple of rocks landed near the bottom and a handful of small streams could no longer flow normally, they would drain off and flow down the sides, creating a more intense flow of water in a smaller area; this would be similar to what might happen if plant species were gone, all of the herbivors would be competing for what is left. Likewise if instead at the bottom the rocks blocked part of top of the waterfall, there would be a more concentrated stream of water that will in turn affect how the remaining streams operate. This is similar to what can happen when there is not an apex predator in the ecosystem. Now with this understanding, one can begin to see how wolves have affected the ecosystem upon their return.
A study was conducted over a period of 15 years after wolves were reintroduced. In this particular study the plant growth was the main focus, however other observations were made about the other wildlife. First off, contrary to popular belief, wolves have caused an increase in elk populations. This increase was caused by how wolves choose their prey. Wolves hunt the weakest members of a herd which are generally the young, sick, and old. It is reasoned that they do this because even with anywhere from 5-10+ individuals in a family group, going after the weakest conserves more energy and therefore allows them to gain the most out of the kill. Even then they do not always succeed every time they hunt. This hunting behavior is far different from human hunters who go for the largest and strongest, which is why their populations are able to improve.
Now even with evidence of wolves causing an increase in the health of elk and deer populations, hunters still say that they cause a decline in their numbers. However that is not so, what is really going on is that wolves have caused elk to change their behavior. This behavior change is documented in another study where they found that elk behaviors changed in order to avoid predation. This was documented by using radio-collars to track herd movement, and they found that there were significant changes. One such change was in their grouping. Before wolves were reintroduced, they tended to remain less clustered and remain mostly in open areas and by streams throughout most of the year. However after wolves had been reintroduced, their seasonal behavior shifted. So during the summer months when wolves would be denning and they would be rearing their young, elk herds remained at higher elevations and stayed clear of areas where wolves tended to den. Then in the winter months they would generally remain in more open areas, grouped close together. This way they avoided steeper snow and lessened the risk of falling prey to wolves. It is this change in behavior that causes the results of the first study mentioned in this section.
Back to the first study involving plant regrowth, due to elk having to change their behavior to avoid wolves, they leave heavily browsed areas for a time. This allows for those saplings to gain some footing and grow. While there is not an immediate growth surge, such saplings as the willow and aspen have been growing more steadily as well as other plant life. With this increase in plant growth, other animals are able to improve as well. For example in the northern ranges of Yellowstone with the increase in willows there is a greater diversity of songbirds in the area. Also beaver populations have increased from just one colony to over ten in a period of seven years after wolves were reintroduced. This was likely caused to the increase of willows. However even though the surge of plant life aided animals in that way, wolves have also aided the bear populations. In other parts of the world where there are bears and wolves, bears often scavenge or steal wolf kills. And in Yellowstone, since they are able to take advantage of wolf kills again, their populations have also improved.