new article about wolves and their impact on elk in YNP

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new article about wolves and their impact on elk in YNP

Post by CLBaileyi » Thu Sep 02, 2010 8:30 pm

Some new research on wolves, elk and aspen in YNP.
Previous research has claimed that the reintroduction of wolves to Yellowstone National Park in 1995 is helping restore quaking aspen in risky areas where wolves prowl. But apparently elk hungry for winter food had a different idea. They did not know they were supposed to be responding to a 'landscape of fear.'

According to a study set to be published this week in Ecology, a journal of the Ecological Society of America, the fear of wolf predation may not be discouraging elk from eating aspen trees after all.

Previous thinking went like this: Aspen are not regenerating well in Yellowstone National Park. Elk eat young aspen. But wolves eat elk. Elk will learn to avoid high-risk areas that wolves frequent. Plants in those areas - such as aspen - will then get a chance to grow big enough so that elk cannot kill them. Eventually, an entire habitat is restored because of a landscape of fear.

Over the last 15 years, the reintroduction of wolves in Yellowstone was heralded as a great success, not only because it reestablished the species, but also because wolves were expected to help restore a healthier ecosystem through such cascading indirect effects on other species.

But this recent study led by Matthew Kauffman, a U.S. Geological Survey scientist, suggests that aspen are not benefiting from the landscape of fear created by wolves, and that claims of an ecosystem-wide recovery of aspen are premature.

'This study not only confirms that elk are responsible for the decline of aspen in Yellowstone beginning in the 1890s, but also that none of the aspen groves studied after wolf restoration appear to be regenerating, even in areas risky to elk,' said Kauffman.

Because the fear of wolves does not appear to be benefiting aspen, the authors conclude that if the Northern Range elk population does not continue to decline - their numbers are 40 percent of what they were before wolves - many of Yellowstone's aspen stands are unlikely to recover. 'A landscape-level aspen recovery is likely only to occur if wolves, in combination with other predators and climate factors, further reduce the elk population,' Kauffman said.

Predators play an important role in ecosystems, said Kauffman, and can influence plants by altering how many herbivores there are (by eating the herbivores) or by changing the behaviour of herbivores (deterring them from areas where predators lurk). He adds, however, that considerable scientific debate exists regarding the importance of these two ways in which predators influence their prey. And this is especially true for large carnivores.

To complicate matters, predators use different hunting strategies - there is the sit-and-wait strategy (as with a spider in a web, or a rattlesnake waiting for a mouse to leave its burrow) and the more active, go get 'em strategy (think cheetahs and wolves). 'So, given that it takes a lot of energy to avoid a predator - energy that could be used to stave off winter starvation - we wanted to find out whether the prey of active-hunting predators such as wolves demonstrated risk-induced changes in areas where they foraged for food,' Kauffman said.

To do this, the authors analysed tree rings to discern when, in the last century, aspen stands stopped regenerating, examined whether aspen stands have begun to regenerate now that wolves have been reintroduced to the park and tested whether any differences in aspen regeneration were occurring in areas considered safe or risky for foraging elk. They used a landscape-wide risk map of elk killed by wolves over the first 10 years of wolf recovery. Finally, the authors experimentally fenced in young aspen suckers to compare the protection afforded to them by wolves versus that of a physical barrier that prevented elk browsing.

'The results were surprising and have led us to refute several previous claims regarding interactions among wolves, elk and aspen in Yellowstone,' Kauffman said.

The tree rings showed that the period when aspen failed to regenerate (1892 to 1956) lasted more than 60 years, spanning periods with and without wolves by several decades. 'We concluded from this that the failure of aspen to regenerate was caused by an increase in the number of elk following the disappearance of wolves in the 1920s rather than by a rapid behavioural shift to more browsing on aspen once wolves were gone from the park,' said Kauffman.

Surveys of current conditions indicated that aspen in study stands exposed to elk browsing were not growing to heights necessary to make them invulnerable to elk. The only places where suckers survived to reach a height sufficient to avoid browsing were in the fenced-in areas. In addition, aspen stands identified as risky from the predation risk map were browsed just as often as aspen growing in less risky areas.

'This work is consistent with much of what researchers have learned from studying wolves and elk in Yellowstone,' Kauffman said. 'Elk certainly respond behaviourally to the predation risk posed by wolves, but those small alterations to feeding and moving across the landscape don't seem to add up to long-term benefits for aspen growing in areas risky to elk.'


Source: Ecological Society of America
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Re: new article about wolves and their impact on elk in YNP

Post by Jayness » Thu Sep 02, 2010 8:52 pm

Great article CLBaileyi, it was very interesting, thank you. =)
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Re: new article about wolves and their impact on elk in YNP

Post by Canidae » Thu Sep 02, 2010 8:53 pm

Ah, good to know, good to know.

I see the March 2010 issue of National Geographic is outdated now; in the article about wolves, they discussed the "ecology of fear" and the trophic cascade. It seems that research has now led to different results.

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Re: new article about wolves and their impact on elk in YNP

Post by Alpha Female » Fri Sep 03, 2010 5:07 am

This is great to know. Thanks for sharing this interesting article with us Bailey!
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Elk numbers not affected by wolf population?

Post by Zethra » Fri Sep 03, 2010 9:24 am

Study shows wolves aren’t helping aspen as much as thought

Wolves have not helped the aspen trees in and around Yellowstone National Park as much as previously thought, a study to be published in the journal Ecology suggests.

The finding challenges the assertion that aspens in Yellowstone had rebounded thanks to wolves, a claim that has become symbolic of the far-reaching affects wolves have on their environment and, for some, a beneficial payoff of the controversial reintroduction.

Researchers with the U.S. Geological Survey, the University of Montana and Humboldt State University have found that elk continue to put pressure on aspen groves, regardless of whether wolves are near.

And, while the Northern Yellowstone elk herd is 60 percent smaller than it was before wolf reintroduction in 1995, "none of the aspen groves studied after wolf restoration appear to be regenerating," said Matt Kauffman, a USGS scientist and lead author of the study.

"Elk forage pretty heavily on aspen and it's really still unknown whether aspen are going to be able to recover," he said.

But while the findings refute what's become a common narrative in the wolf debate - that by eating elk, the predator has allowed aspens and other elk food to rebound from over-browsing -- Kauffman said it shouldn't affect the conversation about the overall worth of wolves.

"I don't think our study has any real bearing on the merits of wolf introduction," he said. "The reintroduction was an incredible wildlife-management success."

Instead, Kauffman said the results clarify the complex relationship between elk, wolves and aspen.

A theory amongst scientists - fleshed out in a widely circulated study published in 2007 in the journal Biological Conservation -- has been that aspen in Yellowstone were regenerating in areas of the park where wolves were common. Elk avoided those areas, the theory went, giving the young aspen a chance to grow to maturity. In other words, wolves acted as unwitting guard dogs for baby trees.

As Science Daily put it at the time, the 2007 results were "especially encouraging for the health of America's first national park, but may also have implications for other areas of the West and other important predators."

But Kauffman and other researchers have since mapped places in the northern elk herd's range where wolves posed a serious risk to elk, as determined by elk kills, and where they didn't. The researchers found aspen trees were browsed in both areas.

And, they found that the elk population in the area is still too large to allow a significant aspen rebound.

"A landscape-level aspen recovery is likely only to occur if wolves, in combination with other predators and climate factors, further reduce the elk population," Kauffman said.
Source - http://www.bozemandailychronicle.com/ne ... 002e0.html



Note from Canidae: This post was originally a separate topic, but I merged it with this one because the articles are very similar.
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Re: Elk numbers not affected by wolf population?

Post by Canidae » Fri Sep 03, 2010 1:11 pm

CLBaileyi posted a similar article here:

http://www.wolfquest.org/bb/viewtopic.php?f=4&t=40420


So I went ahead and merged the topics.
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Re: new article about wolves and their impact on elk in YNP

Post by Willowwolf510 » Sat Sep 11, 2010 4:45 pm

Hmmm..... I had no idea that the aspen were being destroid! I'm glad they're making an effort to restore that. Thank very much for sharing!
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Re: new article about wolves and their impact on elk in YNP

Post by Adalae » Sat Sep 11, 2010 5:54 pm

Thanks for posting this article, CLBaileyi. Very interesting. I hope those aspen trees are able to make a good recovery.
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