From Science Daily:
As wolf populations grow in parts of the West, most of the focus has been on their value in aiding broader ecosystem recovery — but a new study from Oregon State University also points out that they could play an important role in helping to save other threatened species.
In research published in Wildlife Society Bulletin, scientists suggest that a key factor in the Canada lynx being listed as threatened under the Endangered Species Act is the major decline of snowshoe hares. The loss of hares, the primary food of the lynx, in turn may be caused by coyote populations that have surged in the absence of wolves. Scientists call this a “trophic cascade” of impacts.
The increase in these secondary “mesopredators” has caused significant ecosystem disruption and, in this case, possibly contributed to the decline of a threatened species, the scientists say.
“The increase in mesopredators such as coyotes is a serious issue; their populations are now much higher than they used to be when wolves were common in most areas of the United States,” said William Ripple, a professor in the Department of Forest Ecosystems and Society at OSU.
“Before they were largely extirpated, wolves used to kill coyotes and also disrupt their behavior through what we call the ‘ecology of fear,'” Ripple said. “Coyotes have a flexible, wide-ranging diet, but they really prefer rabbits and hares, and they may also be killing lynx directly.”
Between the decline of their central food supply and a possible increase in attacks from coyotes, the Canada lynx has been in serious decline for decades and in 2000 was listed as a threatened species. It also faces pressure from habitat alteration, the scientists said, and perhaps climate change as lower snow packs further reduce the areas in which this mountain species can find refuge.
In numerous studies in recent years, researchers have documented how the presence of wolves and other large predators helps control populations of grazing ungulates including deer and elk, and also changes their behavior. Where wolves have become established, this is allowing the recovery of forest and stream ecosystems, to the benefit of multiple plant and animal species.
Lacking the presence of wolves or other main predators in both terrestrial and marine environments, populations of smaller predators have greatly increased. Other studies have documented mesopredator impacts on everything from birds to lizards, rodents, marsupials, rabbits, scallops and insects. This includes much higher levels of attacks by coyotes on some ranch animals such as sheep, and efforts attempting to control that problem have cost hundreds of millions of dollars.
Scientists have concluded that exploding mesopredator populations can be found in oceans, rivers, forests and grasslands around the world.
“In the absence of wolves, coyote densities and distributions generally expanded in the U.S., into the Midwest, to the northeast as far as Newfoundland, and as far northwest as Alaska,” the researchers wrote in their report.
Where wolves recovered, as in Yellowstone National Park, coyote populations were initially reduced by 50 percent, Ripple said. Although more sampling will be required, early evidence indicates that a snowshoe hare recovery may be taking place.
As these issues are factored into decisions about how to manage wolves, the researchers said, it’s also important to maintain what they call “ecologically effective” wolf populations, the researchers wrote in their study. The full value of these top predators, and the numbers of them it takes to achieve a wide range of ecological goals, should be more thoroughly researched and better understood, they said.
The issue of “mesopredator release” has been studied rather extensively in recent years.
My favorite study on mesopredator release happened in suburban Southern California. Michael Soule found that in areas where suburban coyotes frequented, there were more songbirds. Why? The coyotes in this environment where not the mesopredators. They were the apex predators, and they served the songbirds well. Domestic cats, both owned and feral, are known to be major predators of native birds, but in North America, their kryptonite is the coyote. Coyotes eat lots of cats in suburban environments. And the cats, not being fools, know to avoid areas where they might meet a coyote. It is in those areas of suburban Southern California where songbirds nest. Coyotes really don’t care about bird nests, especially if they are up in trees, but they do care about cats.
In addition to the possible assistance that wolves could provide Canada lynx, it also been established that wolves have helped pronghorns fully establish themselves in Yellowstone. When wolves were extirpated from the Yellowstone region, the coyote population shot up, and the coyotes began to take advantage of many different predation opportunities. When the female pronghorns dropped their fawns, the coyotes would swarm in and catch them. This predation prevented pronghorns from ever establishing the large numbers that had been expected for the species at Yellowstone.
When wolves were reintroduced, the coyote population was halved, and the coyotes tended to stay out of the open areas around the Lamar Valley, where the pronghorns gave birth to their offspring every year.
If wolves succeed in reducing the Canada lynx’s problems from coyotes, it will be a good thing for this species. It is not very common in the United States anymore, but it once ranged rather extensively through the northern tier and down the Rockies.
These lynx do exist in Canada at fairly large numbers, where there are also plenty of wolves. Wolves and Canada lynx really are not competitors. Canada lynx are almost entirely snowshoe hare specialists, and they tend to inhabit much more densely wooded places than wolves do.
However, coyotes do frequent these very densely wooded areas, and they are not above killing a lynx’s kittens. An adult Canada lynx could kill a coyote on its own, but if confronted with a family group of coyotes, my guess is the lynx wouldn’t stand and fight.
The real problem with Canada lynx and coyotes is the same that existed between dingoes and thylacines. Canada lynx are too specialized to one species of prey, while coyotes are generalists, taking not only the lynx’s specialist prey but also other species, which allows their numbers to exploded. In Australia, the thylacines were specialized in hunting small macropods and other smaller prey, but when the dingo or proto-dingo arrived in Australia, they were able to hunt both large and small prey. They were able to take most of the thylacine’s prey from it and augment their diet with large macropods.
Specialization has proven to be the death of so many species, and it would be a shame if the generalist coyote would push the Canada lynx over in this fashion.
So maybe if the wolves do keep the coyotes down, the great northern cat can once again be on the increase.
