Math helps grizzlies to multiply
PULLMAN – Wildlife biologists have employed a lot of tools to influence wildlife populations over the years, from radio tracking to selected hunts to habitat protection.
Robert Wielgus uses math.
Wielgus, a professor of wildlife ecology at Washington State University, is fresh off a sabbatical in Paris, where he spent a year working on algebraic matrices and probability theory, trying to save a tiny population of grizzly bears in the Pyrenees Mountains along the border between Spain and France.
What he discovered confounded the conventional wisdom – rather than suffering from human poaching, the bears were declining because there weren’t enough females, and young, competitive males were wreaking havoc on the cubs.
The problem was the bear equivalent of unruly teenage boys, blinded by hormones. And the relatively simple answer to the problem was to bring a few more females to the dance – something the French government is now doing.
“We used mathematics to save this population, and that’s pretty cool,” Wielgus said last week in his WSU office. “We’re quite confident we are going to see brown bear recovery in the Pyrenees.”
Wielgus has studied bears and other wildlife populations for more than two decades, beginning as a biologist in Canada in 1982. He’d been studying wildlife populations in Manitoba, but the bitter winters made fieldwork unpleasant.
When he had a chance to study bears in Alberta, he took it. Bears, after all, hibernate in the winter.
Wielgus had also incorporated math – statistics, algebra, probability theory – into the study of wildlife, starting with his years in college. He’d done post-doctoral work in France and had relationships with scientists there, and he took a sabbatical for the 2003-04 academic year to work on the math in Paris, while visiting the bears’ habitat.
The number of grizzlies – called brown bears in Europe – in the western Pyrenees had dropped below 10. It was widely assumed that poaching and other human-caused deaths were the problem, given the unpopularity of the bears among the region’s farmers, Wielgus said.
“If we transplanted bears in here, are we just putting more bears into the meat grinder?” he said. “That’s kind of the question. Can we recover these bears?”
Wielgus crunched the numbers for population, survival rates, cub production and a host of other factors, and compared them with a healthier population.
“In the other population, where the population (between males and females) was balanced, everything was fine,” he said.
When there are few females, the large, powerful males hoard them, creating a kind of extended family. But when that large male dies, “three younger guys come to the funeral, and they kill the cubs,” Wielgus said.
This behavior, known as sexually selected infanticide, is not uncommon in wildlife populations, but Wielgus and his French colleagues were surprised that it was the primary factor in the population decline.
“It was a real nice surprise, because this is a problem we can easily solve,” he said.
France is now planning to transplant five to seven Slovakian female grizzlies into the Pyrenees.
Wielgus said the lessons of his work in France could apply here. A struggling population of grizzlies is now living in the North Cascades – and it suffers the same imbalance of males to females.
“You get these males coming in from Canada, and now the population is skewed toward males and so cub production and survival goes to hell,” he said.
For Wielgus – a “math head” – the work on French bears is an exciting confirmation of something that he’s long known.
“The world behaves in a mathematical way,” he said. “There’s nothing magical about it.”