Wednesday, 2 March 2016

The Nature of Fear

The thing I hate about horror movies is the silent moment before something jumps out to scare you. The anticipation and the knowledge that there is nothing you can do to prevent yourself from jumping out of your skin is enough to make you want to hit fast-forward (or just skip ahead if you’re too cool to still own a VCR). The reason you can do nothing to avoid the jolt is because millions of years of evolution have shaped your brain to respond this way. It is a reflex that saved the lives of a good portion of your ancestors over the past 4 billion or so years, as they have been forced to flee from lions, bears, and slightly larger bacteria.

But it turns out that fear isn’t only good for individuals; it can benefit entire ecosystems. Recent research into the interactions between large predators and their prey has revealed that the knowledge that something may be lurking in the bushes, waiting to pounce on you, can change the way you behave just enough to have far reaching consequences. We owe this knowledge to a population of lazy, gluttonous, raccoons who live in British Columbia’s Gulf Islands.

The Gulf Islands are something of a northern paradise. They lie in the patch of sea between Vancouver Island and the North American Mainland. Paddle a canoe along the seemingly infinite coastlines of these islands and you’re likely to see everything from bald eagles, to harbor seals, to killer whales, to sea otters. A few things you likely won’t see, however, are bears, wolves, and cougars. That isn’t to say that these animals don’t belong there; they have just been chased away by decades of humans who value a good view and the safety of their pets over robust food chains.

As a result of the lack of land-based predators, the Gulf Islands are also home to raccoons… a lot of raccoons. Some people would say too many raccoons. The thing about raccoons is that they are smart. They quickly catch on when they have nothing to fear and the consequence is that they will spend literally all day scouring the island’s beaches for clams, crabs, and whatever else they can get their grubby little hands on. This is what science calls a trophic cascade. Remove one species and watch how it all goes south.

University of Victoria PhD candidate Justin Suraci noticed the effect this was having on the ecosystems of those beaches and decided to try an experiment. Suraci rigged up a series of speakers along beaches with particularly bad raccoon problems and began blasting the scavengers with sounds of dogs barking. The results were a 66% reduction in the time the raccoons spent foraging. Suraci also tried playing the sounds of sea lions through the speakers and found that the raccoons just ignored them. Clearly it was fear of a specific predator driving the leaner diet plan. The reduction in foraging time observed on the beaches of B.C. is more than enough for ecosystems within which to stage a recover.

But this isn’t the first known evidence of a trophic cascade caused by removing top predators from a region. Yellowstone and Zion National Parks in the United States have reported that rebuilding populations of wolves and cougars within park boundaries would actually reduce soil erosion and alter the course of their rivers.

In Yellowstone, the extinction of local wolves during the 20th century resulted in an explosion in elk numbers. Those elk graze on the vegetation along the park’s riverbanks and eventually eat all of it away. Plants along a river don’t just look nice, though; their roots actually hold the soil in place against the never ending flow of the river. With less vegetation, the rivers eroded their banks faster and generally started flowing more quickly, altering the environment for the fish and amphibians that depend on them. Since wolves were reintroduced, park officials have noted that the pattern has begun to reverse itself. In Zion, the lack of cougars is presently having the same effect on deer populations and local rivers, but cougars are slower to rebound than wolves.

In the end, it seems that if we want to enjoy the beauty of nature, we can’t pick and choose the animals we want to have around. Especially in the case of predators, removing a single species can have dramatic consequences to both, the food chain and the environment itself. The island-living raccoons in B.C. will soon wise-up to the speaker situation and resume their foraging unless their natural predators are reintroduced. God help us if they figure out how to make cups out of coconuts.