A comeback success story?

It's over 30 years since wolves were reintroduced to Yellowstone but the pay-off for the park is disputed

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THERE'S A LOVELY FILM ON YOUTUBE called How Wolves Change Rivers. Narrated by the British writer and environmental campaigner George Monbiot, and largely drawn from his book Feral, it describes how the reintroduction of wolves to Yellowstone National Park in the US state of Wyoming in 1995 has precipitated a series of ecological benefits. It wasn't just that wolves were hunting and killing herbivores such as elk (animals closely related to European red deer), but were radically changing their behaviour.

"Elk avoided valleys and gorges where they could be easily caught," Monbiot says. "Immediately those places started to regenerate." This is the so-called 'landscape of fear' hypothesis, whereby herbivores come to be afraid in certain areas, and the young trees they might have browsed on survive.

"Bare valley sides became forests of aspen, willow and cottonwood," continues Monbiot. "Then birds started moving in and beaver numbers increased because they like to eat the trees." The regenerating forests stabilised riverbanks, so they were less prone to collapse, and rivers became more fixed in their course. "Wolves transformed not just the ecosystem but its physical geography."

The impact wolves are said to have had in Yellowstone is known as a trophic cascade.

It's a beautiful and uplifting notion but, according to some scientists, total nonsense.

“It is the source of so much confusion,” says Dan MacNulty of Utah State University. “Not just for the general public but among scientists and students, too. I gave a talk at the University of Oxford two years ago, to the biology department, and I had PhD students telling me afterwards that they felt they’d been deceived – which, frankly, they were.”

Tom Hobbs, an ecologist at Colorado State University, agrees with MacNulty, describing the idea of a widespread trophic cascade stemming from the wolves as a great idea that doesn’t hold up.