The world’s monsters are in danger, and that’s a truly scary thing. Researcher have made a strong case over the last few decades that large carnivores are essential ecosystem managers whose influence is felt throughout the food web and affects their prey, their competition and plant life (a ripple effect known as a trophic cascade). They rein in herbivores by preying on them and changing they way they act by creating a “landscape of fear” and keep smaller mesopredators in check through competition and intimidation. With tooth and claw, they regulate some of an ecosystem’s many moving parts, almost always for the better.
Large predators are valuable in less obvious ways, too. By killing and controlling herbivore prey, they help reduce competition between wild and domestic herbivores for grazing, keep diseases from spilling over from one group to the other and give plants the chance to flourish, which helps keep CO2 out of the atmosphere. The carcasses they leave behind feed scavengers and cycle nutrients through the food web year-round, and help buffer the boom-and-bust cycle that climates change creates for these grisly resources. They’re also big business for humans, and help drive tourism revenue from Yellowstone to the Serengeti.
While predators’ place at the top of the food chain is important, it’s also precarious. “These are some of the world’s most revered and iconic species,” ecologist William Ripple and a team of researchers say in a new paper on the state of big carnivores. “Ironically, they are also some of the most threatened.”
Large meat-eating animals tend to mature slowly and reproduce infrequently, keeping their populations low and less dense. They also need a lot of food and have to roam widely to find it, which can bring them into conflict with humans. It’s a perfect storm of traits that makes them vulnerable to persecution, environmental changes and extinction.
In their new paper, Ripple, his frequent collaborator Robert Beschta and colleagues from the US, Europe and Australia take stock of the world’s large predators. They reviewed more than 100 studies to get a clear picture of the animals’ impacts and their conservation status, and the picture they got was not good.
Of the 31 largest carnivores, which are spread across five families – Canidae, Felidae, Mustelidae, Ursidae, and Hyaenidae – 77% are declining in numbers, 61% are listed as threatened by the International Union for the Conservation of Nature and 54% have had their ranges cut by half or more.
Seven of these species are tied to trophic cascades and exert well-documented ecological influences. The rest? We just don’t know. “Many of these species are gradually disappearing just as we are beginning to understand and appreciate their roles in ecosystems,” the researchers write. Any ecological effects they have, especially the species in the tropics and subtropics, are still largely a mystery.
Not that having shown some value to ecosystems has done the “big seven” much good. Leopards are near-threatened and living in less than two thirds of their historical range. Lions are living on less than 20%, and the genetically-unique West African lion has only 250 breeding adults left. The dingo is the sole mammalian apex predator left in Australia, and is excluded from a large swath of the continent by a 3,488 mile-long fence. Wolves were driven out of much of Western Europe, Mexico and the US through the 19th and 20th centuries, and have only started making a (controversial) comeback in the last two decades.
So how did we get to this point? A lot of the blame lies on an apex predator’s only competition: humans. As our populations have grown and spread, there’s less space to go around. We’ve been reluctant to share that space, choosing instead to shoot, poison and trap animals we think of as dangerous, scary and straying a little too close to what’s ours.
If things keep going in this direction, Ripple and his colleagues see two things happening. First, as apex predators disappear, there will be plant species diversity, biomass and productivity will change, influencing “virtually all other species” and ecological processes like disease dynamics, wildfires and carbon sequestration.
Second, they write, “we should expect surprises, because we have only just begun to understand the influences of these animals in the fabric of nature.”
To pull these beasts back from the brink, the researchers suggest global conservation plans that cross taxonomic boundaries and address the traits and challenges that all large carnivores face – like low densities, slow life histories, conflict with humans and need for large habitats. The IUCN has already done something like this with the Large Carnivore Initiative for Europe, and the researchers would like to see this idea expanded with a Global Large Carnivore Initiative. A program like this, the researchers say, would develop and coordinate conservation efforts for large carnivores, educate people about their ecological value and promote human/carnivore coexistence.
These last two goals are especially important and especially challenging. Along with climate change, the researchers say, the slow elimination of large carnivores is one of humans’ most significant impacts on nature, but hasn’t become the same focus of global concern. Carnivores haven’t had their An Inconvenient Truth moment yet. To confront that problem, they suggest a two-pronged approach. First, make people recognize that top predators have vital ecological roles that can benefit humans. Second, frame large carnivore conservation as a moral obligation – there’s an intrinsic value to all species, no matter how sharp and scary their teeth are.
Reference: Ripple W.J., Estes J.A., Beschta R.L., Wilmers C.C., Ritchie E.G., Hebblewhite M., Berger J., Elmhagen B., Letnic M. & Nelson M.P. & (2014). Status and Ecological Effects of the World’s Largest Carnivores, Science, 343 (6167) 1241484-1241484. DOI: 10.1126/science.1241484