Bottom-up is Toppling Down

Apex Predators are Taking It to the Top

I wanted to do a post on the importance of apex predators after writing about shark conservation. The importance of apex predators is always stressed, but I wanted a more in-depth look at it. This article from the National Wildlife Federation explains their role very well and gives several examples of why ecosystem management needs to focus on the top-down approach just as much as the bottom-up theory. The more accepted view on ecosystem regulation is that vegetation and micro-organisms regulate and affect everything above them. However, without the apex predators, the “middle men” usually end up damaging and overrunning the vegetative base and wreaking havoc on the delicate ecosystem balance. Notable examples include:

Orca wal 2 (Photo credit: Wikipedia)

– — Alaskan sea otter populations are dwindling because of a disturbance of orca prey. Because industrial whaling was removing the large whales orcas typically prey on, the orcas were forced to hunt Steller sea lions. The sea lion populations collapsed and pushed the orcas to hunt sea otters. Without sea otters keeping sea urchin populations in check, coastal kelp fields were decimated, destroying vital habitat for fish and other animals.

– — By wiping out wolf packs in Yellowstone, biologists contributed to an elk boom. This elk boom “reduced new growth of aspens on some mountainsides and of willows along streams.” A wolf reintroduction has been underway for 17 years , and there has been positive changes in tree and shrub growth. The vegetation regrowth is crucial for cooling stream water, reducing bank erosion, and, of course, providing habitat for birds and other animals.

– — One of the craziest cases of ecosystem imbalance was when “a population of deer drove a population of black bears to extinction.” I didn’t think something like this would happen, but the deer wiped out the shrubs that the bears depended on for nuts and berries. Unable to consume a third of their body weight a day in berries, the black bears failed to make it through the winter. This was “the only documentation of a large herbivore extirpating a successful and abundant carnivore for a large ecosystem.”

The more obscure results that can be linked to apex predator regulation are carbon emissions and disease control. Because of industrial whaling killing plumpy plankton eaters, the plankton die and sink, rotting on the ocean floor and releasing an estimated 105 million tons of carbon into the atmosphere. The spread of Lyme disease from ticks is strongly linked with declining wolf populations. Wolves, as opposed to coyotes, do not kill mouse-eating foxes. Without mouse-eating foxes, deer mice populations rise, contributing to an increase in the disease. In Africa, the reduction in lions and leopards leads to an increase in olive baboons. Olive baboons frequent human areas and this leads to a rise in intestinal parasites for both the humans and baboons. I don’t want to add much more, but it’s obvious a balance in “the circle of life” is needed for a healthy ecosystem. From what I can tell, ecosystems have a way of balancing themselves pretty well when left alone. The common factor in all of these imbalances is the apex of apex predators: humans. We hunt the whales and sharks. We introduce deer and other unnatural species into areas. We eradicate other species because we see them as a nuisance. I think actually finding an ecosystem that became unbalanced for reasons other than humans would be quite a feat. If you know of any examples, please comment. I’d love to read about them!