The Managed World: A Tale of Two Trophic Troubles

Macquarie Island, before and after cat elimination. (From 80 Beats at Discovery Network)

There is no place on earth, no matter how remote, untouched by humans. We are mighty: we can trawl the deep, explore the South Pole, and fish every single island in the South Pacific. But as every young nerdling knows, with great power comes great responsibility. The Managed World is an occasional series in the Oyster’s Garter that explores the hard choices that come from a human-dominated world.

Most food webs look more like a tangled web than the Great Chain of Being – since predators eat each other and most animals eat more than one prey species, their relationships are complicated. But sometimes changing the population of a single predator can bring the entire ecosystem down like dominoes. It’s called a trophic cascade.

The New York Times has two examples of humans changing the populations of key species, and the consequences that result. The first took place on Macquarie Island, a small island between Australia and Antarctica. Like on many isolated islands, the native birds evolved without predators and live in burrows. Introduced cats were eating the birds and running amuck. So researchers embarked on an intensive cat-elimination program. Sounds good so far – kill the kittehs, save the birds.

Elk feeding. (NYT)

The only problem is that there are also introduced rabbits and introduced plants. With no more cats, the rabbits bred like rabbits and ate all the native plants. Introduced plants took over the bare slopes and prevented the native birds that this was all supposed to help in the first place from nesting in the best burrowing sites.

The second involves a lawsuit over feeding elk in Jackson, Wyoming. When elk were depleted and starving at the turn of the century, people started feeding them. Now Jackson has an elk overpopulation that eats all the native willows and breeds disease (that can then be passed on to cattle). But if the lawsuit wins, stopping the elk feeding would cause a kind of economic cascade – there’s an entire tourism economy built around the easy-to-find elks. And while unnaturally large populations of elk breed disease amongst themselves, starving elks stealing cattle feed would pass disease, too. So nobody knows what to do. (I don’t suppose anyone wants to introduce more wolves? They’re proven to control elk and I bet they’re good for tourism!)

The conclusion: it is  very, very hard to predict (as Donald Rumsfeld would say) the unknown unknowns. There’s a million stories like these – even Lyme disease in the Northeast is thought to be connected to a trophic cascade with wolves, deer, mice, and ticks. To end with a slight non sequiter, this is why I’m leery of geoengineering. If we can’t even properly manage the ecosystem of 21-mile-long Macquarie Island, I worry that the cure for global warming could be even worse than the disease.


7 Responses to The Managed World: A Tale of Two Trophic Troubles

  1. whysharksmatter says:

    Have you seen the research about how the loss of sharks, through trophic cascades, results in algal takeover of coral reefs? Similar stuff. Predators are important.

  2. J.P. says:

    Time to introduce the Elk Burger.

  3. […] a followup on my post on human intervention in the food web, our Dutch correspondent JP reports that the harsh winter has killed a third of the animals in the […]

  4. Peggy says:

    Way way back when I was in elementary school, we put on a play about a cascade of unintended environmental consequences based on this book, which starts with spraying DDT to eradicate malaria-spreading mosquitoes and ends with dropping cats (with parachutes) onto remote villages in Borneo. I don’t know how all of that eventually panned out – hopefully, the cats didn’t destroy all of the non-disease carrying local fauna.

    Stories like the ones you link to are a clear reminder of how difficult it is to predict what the consequences of environmental interaction will be.

  5. Peggy, “parapussycats” made my day! That is an amazing story. Sadly, feral and domestic outdoor cats are usually very ecologically destructive – they’re listed in the top 100 of the world’s worst invasive species. Cats are just as happy to kill native lizards and birds as pesky rats and mice and can really damage local environments. That’s why my beloved kitties are strictly indoor-only. (Well, that and the cat-eating coyotes in the nearby canyon.)

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