Balance of nature: wolves influence elk adaptations (Introduction)

by David Turell , Wednesday, September 05, 2018, 21:17 (2270 days ago) @ David Turell

It turns out Yellowstone wolves prefer to attack elks who have shed their horns, and that timing has shifted:

https://www.sciencedaily.com/releases/2018/09/180905113232.htm

"They discovered that wolves in Yellowstone National Park preferentially hunted bulls who already had shed their antlers over those who still had them during late winter. The finding suggests that antlers are used for more than just competing for cows -- that they help deter predators, too -- which could help explain why bulls shed their antlers long after the rut.

"'Because wolves often prefer elk in these systems, male elk uniquely keep their antlers for much of the winter," Metz said. "Other species, say moose in our study system, shed their antlers beginning in December. We believe elk evolved to keep their antlers longer than any other North American deer because they use their antlers as an effective deterrent against wolf predation."

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"Bulls shed their antlers beginning at the end of each winter and immediately start growing another set. Getting rid of antlers as soon as possible removes a cumbersome burden and gives individual bulls a jumpstart at growing antlers for next year's rut.

"But as a whole, elk shed their antlers months later compared to other North American deer species, and shedding is staggered over a two month period beginning in March, suggesting there might be other reasons to keep antlers around a little longer.

"'Antlers are the product of sexual selection, where males are competing over breeding opportunities in a short time window in the fall," Metz said. "Here we show that the evolution of antlers was also influenced by other things in an elk's environment, like wolf predation, and that a secondary function also helped to shape the characteristics of this structure, such as when antlers are shed."

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"Wolves in Yellowstone often kill bull elk during the winter months, but Metz and his co-authors found that wolves strongly preferred to kill individuals who had already shed their antlers -- even though they were often in better condition than bulls who still had their rack. The results showed that antlers are indeed an important predatory deterrent for elk -- a secondary function that could help explain variation in antler retention time across species in temperate climates.

"'These males that shed their antlers first are more vulnerable to being killed by wolves despite being in better nutritional condition," Metz said. "The individuals who are in the best condition are the first to drop their antlers to get a leg up on growing larger antlers for the next season and therefore gain the greatest reproductive success. Wolves mostly target individuals who are very young, old or in poor nutritional condition, which are characteristics that make them vulnerable. Here we identified a new, unexpected vulnerability -- shedding antlers early."

"The study highlights an evolutionary Catch-22: Weapons come with both benefits and costs. Bulls who drop their antlers early may grow relatively larger antlers in the upcoming year, winning more cows, but they're also at greater risk to become dinner first."

Comment: Another ways a top predator influences the homeostasis of natures balance.