The world’s largest carnivores are facing declines in both population and range, jeopardizing their long-term viability while hinting of a larger ecological disaster, according to a new study published Thursday in the journal Science.
Co-authored by researchers at the University of Montana, the study found that 17 of the planet’s 31 largest carnivores now occupy less than half of their traditional range, placing them at risk of eventual extinction.
The study also found that 77 percent of those species, which include the tiger, lion, dingo and puma, among others, are dwindling in number. Further declines could alter the diversity of plants and impact other animal species, including humans.
“If carnivores are important, what’s their conservation status?” said Mark Hebblewhite, an associate professor of ungulate habitat ecology at UM and one of the study’s authors. “To me, it’s the main message I’ve taken from our work.”
Hebblewhite is currently in Italy studying the effects of climate change on roe and red deer, and helping with efforts to drive the successful reintroduction of the brown bear to the Alps, one of Europe’s great mountain chains.
The conservation efforts taking place in other parts of the world – including Hebblewhite’s scientific sabbatical in Italy – resemble those that have unfolded across the Northern Rockies over the past three decades.
The Greater Yellowstone region has given birth to several conservation success stories, and when Hebblewhite looks to Montana, he sees the makings of an international how-to guide, one that includes programs to help humans coexist with carnivores, even when it may not be convenient to do so.
Wolves, he noted, have reclaimed their rightful place in the ecosystem, grizzly bears are near recovery and programs to compensate ranchers for livestock losses are in place. It’s those lessons that need to go global, Hebblewhite said.
“It’s hard to not feel successful when we look around Montana,” said Hebblewhite. “But when we look around the world, that success isn’t there. We’re in real trouble in some places. The large carnivores are disappearing extremely fast from different parts of the world.”
Hebblewhite cites tigers as an example. Once 100,000 strong at the turn of the 20th century, the species is down to an estimated 3,000 wild animals that occupy just 18 percent of their historic range.
To help the tiger’s recovery and teach a message of coexistence, Hebblewhite looks to UM and the university’s role aiding global wildlife conservation. He cites the work of Tshering Tempa, a UM wildlife biology student from Bhutan, who has returned to his country to help keep tigers on the landscape.
“When I put on my education hat, one of the things we do well at UM – and one thing I’m most proud of – is that we use the lessons we’ve learned in Montana from wolf and grizzly bears, and we transfer them to other parts of the world,” Hebblewhite said. “Compared to the rest of the world, we’re doing pretty well. We have a lot to teach and we’ve also got a lot to learn.”
The learning curve may be growing shorter, and as science gleans answers by observing nature, it’s looking to apply cures on a global scale, and do it sooner than later.
The new study notes the urgency, saying the status of large carnivores will have wide-ranging consequences on other species, and will “influence numerous other ecological processes, including disease dynamics, wildfire, and carbon sequestration.”
To make their case, researchers reviewed the conservation status and ecological function of the planet’s 31 largest carnivore species – those with a body mass greater than 15 kilograms.
Overall, the order of carnivores includes 245 species that live in nearly every major habitat on the planet. They are naturally rare due to their position at the top of the food chain, and they are both prized and revered because of it.
Rare though they are, even large carnivores have positive impacts on the structure and function of a diverse ecosystem. Without them, the diversity of plant species is reduced, holding further implications to other animals.
“We’ve watched it happen,” said Hebblewhite. “Without large carnivores, we get an overabundance of primary prey, like ungulates in North America. We suggest that losing a population of large carnivores doesn’t just impact that species, but an entire landscape.”
The examples aren’t hard to find and the study cites many of them. In the absence of pumas in the eastern U.S., for example, the deer population has exploded. The result has altered the function of the larger ecosystem, including plant recruitment and survivability.
Yet in other regions of North America where pumas remain, they work to limit mule deer densities, helping free woody plants from grazing pressure. That affects other land and water species, including wildflowers, amphibians, lizards and butterflies.
Similar results were observed in other species, including non-carnivores. The pressures hunters place on moose has resulted in more willow production, encouraging an increase in the abundance of migrant birds. The overabundance of deer in Germany has prevented that country’s efforts to restore its forests.
The study also looked at the sea otter as one of the world’s large carnivores. When the species was present in its native habitat, all species thrived. When they were absent due to hunting pressures, the balance tipped in favor of sea urchins, holding consequences for other species, including the killer whale.
“Without the otter, it became a sea urchin desert,” Hebblewhite said. “There were no fish, no biodiversity and no kelp.”
Habitat fragmentation, the lack of connectivity, climate change and the global population of humans are also discussed in the study, the later cited as one of the greatest threats to carnivores due to resource consumption.
Hebblewhite said more work is needed to further understand the benefits of having large carnivores on the landscape, along with the leading conflicts between carnivores and humans, and what management practices will help sustain the balance into the future.
“We need to understand how carnivores, like wolves, interact with the entire ecosystem in ways that sometimes benefit us, or sometimes cause us temporary inconveniences,” said Hebblewhite.
“It really comes down to helping individual ranchers, whether they’re in Montana or Africa,” he added. “How do we help these people live with carnivores? That’s what we do at the university, helping fill that role of spreading the research.”
Hebblewhite co-authored the study with Joel Berger, a professor of wildlife conservation at UM and the John J. Craighead Chair. They were joined by researchers from the universities of California and Yale, Oregon State University, and scientists in Australia, Italy and Sweden.