Keystone predators run the ecology

kw: book reviews, nonfiction, ecology, predators, extinction

Prior to about 1965, when we visited California we would always spend one day at the tide pools near Newport Beach or Laguna. We typically collected some of the empty shells, and one time we took home a few starfish, killing and preserving them with salt. The common starfish Pisaster ochraceous is a big, strong sea star, up to a foot across. We learned not to bother the ones that were humped up over a mussel; such a one was busy pulling the shellfish open to eat it.

After 1967, when I moved to California, I found that most of the tide pools had been closed to collecting. A few years later, many of them were closed to all foot traffic. They were being "loved to death" by too many visitors. The amount of collecting had messed up the ecology, and later just the things killed by being walked on continued to mess it up.

Unbeknownst to me, Robert T. Paine had already established that the removal of starfish from tidal rocks and pools seriously damages the entire ecology. By removing all the stars from one pool and leaving the one next to it alone, he found that the mussels in the pool without starfish spread to take over the whole pool, driving out every other species. A healthy pool that includes starfish has dozens of species of animals and algae. While it may seem that Pisaster is a disaster for mussels, it is necessary for a balanced ecology in the intertidal zone.

Thirty years later in Yellowstone National Park, wolves were returned to the Park in 1995 after nearly seventy years of exile (the last Yellowstone wolves were trapped in 1926). During those seven decades the Park's population of elk increased by a factor of between ten and 100, and other changes occurred in synchrony: streams became muddy, aspen and willow stands shrank, and large areas took on a clipped aspect.

The return of wolf predation didn't do much to change elk numbers, not at first. But it sure changed elk behavior. Willow and aspen began to grow again at stream margins, particularly at the inside of bends, because these were places where an elk is less likely to be able to fight off or outrun a pack of wolves. The elk quickly learned to avoid such traps, even though their favorite foods began to grow there in abundance.

All this and more is described by William Stoltzenburg in Where the Wild Things Were: Life, Death, and Ecological Wreckage in a Land of Vanishing Predators. The premise of the book is simple: the keystone species of nearly every ecological habitat is a scarce predator, whether starfish, wolf, orca, eagle or lion. If too many of these predators are removed, the ecology rebalances, typically by some formerly intermediate species increasing and most others vanishing.

This is strongly expressed by the example in the chapter titled "Little Monsters' Ball". A typical American suburb is dominated by "mesopredators" such as raccoons, rats, foxes and "outdoor" cats and dogs. Just house cats are thought to destroy a billion small mammals (mice, voles, and moles, for example) and half a billion songbirds each year across the U.S. For every "trophy" your cat brings to your door, one or two might have been eaten and one or two others were left to rot or left dying when the cat got tired of playing with it. Multiply by fifty million cats.

By contrast, in areas patrolled by coyotes, the cats (and dogs and rats and raccoons) spend more of their time staying out of the way of the "song dogs". In one study, 20% of coyote scat samples contained house cat remains. As a result, not only are there more small mammals and songbirds—five times as many—but there are also more butterflies and a wider variety of plants.

At one time, the American continent had a full measure of larger predators: pumas (AKA panthers), wolves, lynxes, bears, eagles and falcons. There were plenty of mesopredators such as raccoons, and large herds of grazers such as deer, but fewer of either than we see today. And there were lots of the littlest animals. At an even earlier time, there were a few of the largest predators: a larger lion, cave bears twelve feet tall, and saber-tooth cats, preying on even larger prey such as mammoths and giant sloths.

All the largest denizens of North America disappeared in suspicious synchrony with the invasion of the continent by Siberians more than 13,000 years ago. The "primeval" America reported by the Spanish and others after 1492 was actually impoverished compared to the America seen by those Siberians, who went on to become Cherokees, Apaches, Arapahoes, Navajos and others we used to call "Indians".

There is a move afoot to "rewild" America, to re-introduce elephants into the wilderness, and to restore many more former populations of wolves, mountain lions (puma or panther) and grizzlies. This doesn't go down well with Homo suburbica. The vast majority of Americans get just about all the "nature" they can handle from the occasional bee sting and spreading deer repellent around their gardens. They are actively hostile to the idea that they might one day have to be on guard for large predators roaming the woods right next to their neighborhoods.

A few years ago, there was a puma loose in northern Delaware and southeastern Pennsylvania. A few people got a thrill out of the idea. I remember seeing the tracks in the snow around a building near the one I work at, a building that housed laboratory animals. The big cat could smell the lab rats, but couldn't find a way in to get at them. The cat resided for a few days at a YMCA camp near Wilmington, but it was winter so no events were scheduled. I wonder what people would have done if a mountain lion strolled through during the peak of swimming and soccer season! The cat eventually strolled over into Maryland, and I haven't heard whether it is still on the loose.

The author notes that it is probably too late to recover America's lost ecological glory. With care, a couple hundred wolves can be tolerated at Yellowstone, a few dozen pumas in park areas outside San Diego, but the first time somebody's kid is eaten, all kinds of crap will hit the fan, and I suspect that a number of policies of the EPA will wind up in tatters. I don't see much chance for rewilding.

But we must take responsibility for what we have wrought. The single biggest ecological problem in America now is the huge herds of deer, that have no lions or wolves to regulate their numbers. I propose that it is the patriotic duty of Americans to lobby for full-year deer season and for $1 maximum for a deer license, to get licensed, and, with borrowed artillery if you don't own any, take at least one deer home every month and put it in the freezer. Only sworn vegetarians would be exempted from this duty. Venison is quite a bit healthier eating than beef.