Oh dear, I thought this morning upon reading “Is the Wolf a Real American Hero?,” an op-ed piece in the New York Times by Arthur Middleton, a post-doctoral student. This is going to make lots of people hopping mad, and for no good reason. It comes on the heels of another challenge to the trophic cascade theory in Nature, by writer Emma Marris. Her piece is “Rethinking Predators,” and like Middleton, most of her evidence actually supports the assertion that carnivores at the top of the food chain have a big effect on what comes below. Yet both Marris and Middleton frame their pieces as take-downs of science done by scores scientists over decades of peer-reviewed research.
I first learned about trophic cascades while working on my book, The Spine of the Continent. I hung out with a bunch of researchers on a “science hunt” at a ranch in Colorado. There is a sentiment among some ranchers that scientists are all against hunting, and this is not the case; so the annual science hunt is something of a public relations event to demonstrate that people with PhDs also shoot large animals. They don’t usually shoot top predators though – they go for ungulates like elk and deer, and largely profess to shooting only what they will eventually eat. We’re all part of the food web, after all.
One of the younger researchers on the science hunt told me he had reservations about the idea that the top predator in an ecosystem has such a big effect on all the interactions that go on in it. Bottom up forces, starting with the plants that photosynthesize sunlight, to him represent a bigger lever in nature. Fair enough, right? I for one, am completely able to hold in my mind the concept that both top down and bottom up are at work here.
Recently I interviewed Justin Brashares, a U.C. Berkeley professor who has studied trophic cascades very closely. Brashares’ most recent research concerns not the top or the bottom but the middle of the trophic connection (‘trophic’ by the way, means ‘food,’ and cascade, of course, means to fall). With other researchers he’s studying the effects of losing hippos in an ecosystem. Hippos are herbivores and in Brashares’ study site they forage at night and poop in their water in the day. The aquatic result is thronging with biodiversity that disappears when the hippos go away. Doesn’t it just make even more common sense that OF COURSE the middle of the food chain is important too?
It’s fine, of course, to look under the hood of received wisdom, to challenge ideas that have become convention. But why take this big fake pose against decades of science? In the case of Middleton’s piece, there are simply truckloads of research showing that the reintroduction of wolves to Yellowstone has restored ecological resilience there. Middleton says the wolves haven’t restored Yellowstone to what it was before predators were removed. Okay, but does that mean that they’re dispensable? His challenge implies as much. He glosses over the very fact he recounts, which is that yes, wolves have had a big effect on the Yellowstone ecosystem.
There are better windmills to be tilting at. The rest of us don’t need to have absolutes declared about nature. Is the predator absolutely the big force, or is the vegetation absolutely the big force? Wait a minute, maybe the hippos are the big force? The point is all of the players in the ecosystem are important. It’s a cycle. It’s an interaction. It’s a “tangled bank,” as Darwin put it. We are pulling some of the tangle out at a greater rate than we are pulling out others. Top predators are under siege. Usually they are most directly threatened by ignorant, disenfranchised, underemployed white men who have a lot of guns. Now it seems, journalists and academics are finding them an easy shot too.