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What happens when we mix a biologist who studies beetle horns with scientists who are exploring predator-prey dynamics? You understand better why elk lost their wood much later than males of all other North American species.
University of Montana researchers and their partners recently published a study on Ecology of nature and evolution telling an evolutionary link between wolves and the moment when bull elk lost their antlers.
The authors were Matt Metz, doctoral candidate at UM, as well as UM co-authors, Doug Emlen and Mark Hebblewhite, Dan Stahler and Doug Smith of the National Park Service, and Dan MacNulty of the Utah State University.
They found that the wolves in Yellowstone National Park preferentially hunt for bulls that had already shed their antlers over those that still possessed them at the end of the winter. The findings suggest that woods are not only used for competition with cows, but that they also help deter predators, which could explain why bulls lose their woods long after the rut.
"As wolves often prefer elk in these systems, male elk keep their woods uniquely during most of the winter," said Metz. "The other species, let's say the moose in our study system, are losing their antlers from December, and we think elk have kept their woods longer than any other northern deer." because they dissuade them effectively against wolf predation. "
The woods have evolved to improve breeding success. The bigger the woods, the more likely the bull is to produce cows in the fall. In many species, these types of weapons also serve secondary purposes, but these reasons are not always well understood, as is the case for elk.
The bulls lose their woods at the end of each winter and immediately begin to grow another set. Getting rid of the woods as soon as possible eliminates a heavy burden and gives a boost to the growth of wood for the animal next year.
Overall, elk lost wood months later than other deer species in North America, and the fall is spread over a two-month period beginning in March, suggesting
"The woods are the product of sexual selection, where males compete for breeding opportunities in a short time in the fall," Metz said. "We show here that the evolution of woods has also been influenced by other factors in the elk environment, such as predation by wolves, and that a secondary function has also helped to shape the characteristics of this structure, for example when the woods are poured. "
Metz, a longtime researcher of the Yellowstone Wolf, has analyzed more than a decade of data from the Yellowstone Wolf Project, a long-term study of the interactions between wolves and their prey.
Yellowstone wolves often kill bull elk during the winter months, but Metz and his co-founders found that wolves strongly preferred to kill individuals who had already lost their antlers – even though they were often in danger. better condition than bulls. The results showed that antlers constitute an important predatory deterrent to elk – a secondary function that could explain the variation in wood retention time in temperate climate species.
"Those males who lose their antlers first are more likely to be killed by wolves, although they are in better nutritional condition," Metz said. "People who are in the best condition are the first to drop their woods to grow larger woods for the next season and therefore have the greatest breeding success.The wolves primarily target the very young, old or poor nutritional status, which are characteristics that make them vulnerable.Here we identified a new, unexpected vulnerability – early wood loss. "
The study highlights an evolutionary takeover: weapons have both benefits and costs. Bulls that lay their wood early in the morning may have relatively large woods in the next year, gaining more cows, but they are also at increased risk of becoming the first to dine.
In any case, for young bulls that will probably not succeed in the future rut, the risk is too high. These males are among the last to throw their woods.
Metz has earned a B.S. in UM wildlife biology and has studied predator-prey dynamics in Yellowstone since 2002.
"The study started with observations I made when I was working as a seasonal field technician for the Yellowstone Wolf project in the early 2000s," he said. "We usually see deer antlers from the end of March, but the winter of 2004-05 was milder and the bulls lost their woods a little earlier."
One day, he and another researcher spotted a moose killed by the wolf.
"We came in, and it was a woodless male in early March," Metz said. "We had not seen any bull elk living in the landscape yet." We thought: "It's pretty interesting. "We just started to notice this relationship where we were seeing wolves meeting male elk, and they seemed to be focusing on those who had already lost their antlers.It took 13 years of data to test this idea."
Along the way, Metz recruited other co-authors, including professors UM Hebblewhite and Emlen.
"For me, one of the most interesting aspects of this project is its start-up," said Hebblewhite, professor of wildlife biology at WA Franke College of Forestry and Conservation at UM, which focuses on the predator-prey systems of large mammals. "It started with Matt just being attentive, noticing something in nature, then diving into more than a decade to find out why – it's the heart of the scientific process."
Hebblewhite has been studying wolves and their prey for a quarter of a century, but it's the first time that he's stopping to think about what makes woods. "Most of the time, the reasons we study nature are to control or manage it, to have it do what we want for us," he said. "It's a case of wonder at its best."
Emlen, an evolutionary biologist and professor in the Division of Biological Sciences, said the nature of the collaboration, which crossed departments and disciplines, was the most fun.
"Matt is a wolf biologist, and Hebblewhite is an elk biologist, but he does not focus on the woods," Emlen said. "I work on rhinoceros beetles and study animal weapons – beetle horns, I spend most of my time thinking about big arms, so it was great working on woods because are giant weapons A beetle biologist who studies guns can collaborate with elk and wolf biologists.
The study was funded in part by the National Science Foundation's long-term research program in environmental biology, which aims to support research projects lasting 10 years or more.
"It's a very sophisticated look at complicated behavior," said Kendra McLauchlan, director of the NSF program. "They have been able to make this discovery because of 13 years of careful observation.Sometimes it is really important to have this record of long-term observations."
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