An epochal study published Friday in the journal Science paints a truly frightening picture of a world without large carnivores, and a couple of Californian predators play a leading role.
The study, "Status and Ecological Effects of the World's Largest Carnivores," examined more than 100 recent surveys of the roles that the world's largest predators play in shaping the ecosystems that they live in. They found that removing predators from an ecosystem can cause that ecosystem to unravel, with effects ranging from increase in pest animals to rivers changing course.
The paper is a compelling confirmation of something wildlife biologists have long suspected, and the implications for California, where predators large and small have been systematically removed for more than 150 years, are troubling.
The study surveyed seven of the world's 31 largest predators. Two examples in particular are of immediate interest to fans of Californian wildlife: sea otters, which maintain the health of the state's kelp forests by eating the sea urchins that eat the kelp, and mountain lions, which help maintain the state's forests by eating mule deer and Columbian black-tailed deer, which devastate broadleaved trees and shrubs if left uncontrolled.
Appealingly, the researchers also found that protecting mountain lions help boost populations of butterflies, presumably by limiting browsing pressure on larval food plants. A healthy mountain lion population also helps maintain habitat for frogs, salamanders, lizards, and snakes.
The other carnivores examined in detail by the survey were lions, leopards, the Eurasian lynx, dingoes, and gray wolves. (Only the last was historically native to California.)
All of the carnivores studied are in trouble, with threats ranging from climate change to trophy hunting to loss of habitat. And all those threats have a common basis: competition from humans.
(As if to underscore the urgency of the topic, an unrelated paper published Wednesday in PLOSOne reveals that West African lions are critically endangered.)
Each of the threatened carnivores turns out to play a startlingly important role in maintaining ecosystem health. Take the previously-mentioned "rivers changing course" issue: when predators are removed from an ecosystem their prey multiply, causing increased damage to streamside vegetation and trampling riverbanks. Riverside vegetation controls erosion: without it, seasonal floods become more damaging and rivers can actually jump their banks.
And as in the case of the sea otter and sea urchins, losing a predator can mean that an entire ecosystem, which may support hundreds of unique species, can fall apart.
As the plight of the world's carnivores deepens, such consequences may become more severe. "Globally, the ranges of carnivores are collapsing and many of these species are at risk of either local or complete extinction," said William J. Ripple, Oregon State University professor and lead author of the paper. "It is ironic that large carnivores are disappearing just as we are learning about their important ecological and economic effects."
Until the 20th Century California was home to quite a few large carnivores, including what may have been the world's largest subspecies of grizzly bear. The state was home to both northern and Mexican gray wolves, wolverines, and much larger populations of the mountain lions and bobcats that wildlife advocates now struggle to protect.
Those two cat species have recently won increased protection in the legislature, with new regulations on puma encounters and limits to bobcat trapping both winning much-lauded signatures from the Governor in 2013. But the state's most common large predator, the coyote, enjoys almost no protection in the state of California. In fact, the state's Fish and Game Code classifies the coyote in the same category as invasive pest species such as the starling and European sparrow, which can be shot any time of year in any place where a firearm can be legally discharged, as long as the shooter has a hunting license.
That policy proceeds despite abundant scientific data showing that hunting coyotes actually serves to increase their population, by disrupting family units in which only the parents breed.
Though some people maintain that human hunters can replace large carnivores' ecological services, Ripple and his colleagues dispute that, pointing out that human hunting, with its seasons and its reliance on road access, cannot duplicate the 24/7, whole-landscape hunting patterns of wild predators:
In the end, it is not surprising that various human activities in Australia, North America, and Eurasia have been unsuccessful in substituting for large carnivores to control populations of native and nonnative herbivores and mesopredators. The huge importance of carnivores is exemplified by the fact that humans typically cannot replicate the effects of carnivores on ecosystems.
The authors call for a world-wide effort to protect large carnivores based on Europe's Large Carnivore Initiative, a project of the International Union for the Conservation of Nature (IUCN). The paper ends with a call to action that's fairly remarkable for a scientific paper in one of the world's top two peer-reviewed papers:
[L]arge-carnivore conservation might also be seen as a moral obligation -- the recognition of the intrinsic value of all species. A 40-year history of the field of environmental ethics has both rigorous and systematic rationales for valuing species and nature itself. Large carnivore conservation, therefore, might benefit greatly from a more formal relationship with practitioners of environmental ethics. It will probably take a change in both human attitudes and actions to avoid imminent large-carnivore extinctions. A future for these carnivore species and their continued effects on planet Earth's ecosystems may depend upon it.