Why we need predators

Predators have an image problem. It’s not that surprising since many of them, especially the largest species, are capable of causing havoc by killing the things we like to eat — or us. But it still surprises me whenever I run across people who advocate getting rid of predators, especially when these animals aren’t a problem in their daily lives.

Over the summer I got into an argument with my trainer about killing off sharks, after a spate of shark attacks made the news. Besides being a threat to people, sharks drive tourism away from some areas, he reasoned, and killing them would prevent that. At the time, my brain, focused on exercise, could come up with no more than “bad stuff happens when you kill off predators” as a response. But there’s evidence to back up my statement. For example, after the decline of big shark species in the coastal northwest Atlantic, most species they preyed upon increased. Sounds good, right? Well, not if you like scallops. The cownose ray was one of the species that benefitted from the lack of big sharks. But the ray feeds on bay scallops. More rays meant fewer scallops — enough so that a century-long scallop fishery collapsed, scientists reported in Science in 2007.

The sentiments of my trainer aren’t unusual. Last week, Quartz published a baffling article advocating the elimination of all wild predators “to truly end animal suffering.” (No, it’s not satire.) That would not, of course, end animal suffering because in the upended food webs that would result, animals would trade death by predator for death by disease or starvation — with plenty of suffering to go around.

What would that look like? Just consider the deer population in North America. Without predators, deer have proliferated, threatening gardens and, worse, spreading Lyme disease. Attempts to control the population with hunting are not popular, and sterilization is expensive and not always effective (wasting your tax dollars). Not doing anything, though, lets the deer get out of control. It’s more animals for hunters, but also more to be hit by cars and lost to lack of food.

Another example comes from Australia, where dingoes help to keep herbivores under control. Without them around, kangaroos (the “deer” of Australia) and introduced foxes increase in number, leading to declines, and even extinctions, in small native animals and grasses.

Large carnivores, the really scary animals that are easy to hate, are on the decline worldwide. That has led to numerous changes to ecosystems, William Ripple of Oregon State University in Corvallis and colleagues noted in Science last year. When carnivores are removed from an ecosystem (or returned to one), there are cascades of changes to the local food web.

“Unexpected effects of trophic cascades on various taxa and processes include changes to bird, mammal, invertebrate and [reptile and amphibian] abundance or richness,” they note. There can also be changes to disease dynamics, patterns of wildfire, carbon sequestration and other ecological processes. And that is just what scientists know about: “We should expect surprises, because we have only just begun to understand the influences of these animals in the fabric of nature,” the team writes.

We probably have only a fraction of appreciation for the benefits that predators have for their ecosystems and, thus, for us. But faced with millions of years of evolution that have trained us to be fearful of — and hate — these animals, it may take a long time for them to obtain a successful image overhaul. We can only hope that happens before they are all gone.