It's their naturally small populations that also leave these predators vulnerable. Indeed, since prehistoric times, humans have had a hand in driving massive predators extinct, including saber-toothed cats and giant reptiles. More recently, habitat destruction and poaching have pushed many key predators, including the Siberian tiger, the great white shark and the Ethiopian wolf, to the brink of extinction. And when predators disappear, ecosystems start to unravel.
When an ecosystem loses a key species, it triggers what ecologists call a trophic cascade—a butterfly effect that spirals down the food chain. A well-documented case study for this phenomenon is the gray wolf, once among the world's most widely distributed mammals. Historically, gray wolves roamed the entire northern half of the Americas, but by the mid 20th century, aggressive hunting campaigns had all but eliminated wolves from the lower 48 U.S. states.
Prior to their extirpation, North American gray wolves were a key predator of deer, elk, moose, bison and caribou, as well as numerous smaller mammals. Following the wolves disappearance, the abundance of deer skyrocketed, with some populations climbing to six times their historical size. Unchecked, deer are like lawn mowers, stripping bark off of trees and decimating understory plants. This, in turn, can diminish the amount of carbon a forest stores, impact plant diversity, and weaken the forest's resilience to future disturbances. As reported last year inScience, the recent reintroduction of wolves to Yellowstone National Park has allowed some of the most deer-decimated stands of forest to heal, increasing their carbon sequestration potential.
Wolves provide other crucial services as well, such as quelling the spread of infectious disease. In recent decades, Lyme disease, a tickborne illness found across North America, has been on the upswing, with some areas seeing a 1000 percent rise in disease incidence. A 2012 studywhich appeared in the Proceedings of the National Academies of Sciences demonstrated how the spread of Lyme disease is the result of a complex trophic cascade beginning at the top of the food chain. Since the disappearance of gray wolves, coyotes have, in many places, been elevated to top-predator status. Coyotes prey on smaller carnivores including foxes, which in turn hunt small, herbivorous mammals—the primary carriers of disease-ridden ticks. More coyotes means fewer foxes, causing populations of Lyme disease-carrying rodents to boom.
It's clear from ecological studies that wolves do far more than just keep the deer in check—they're the lynchpin holding together the very fabric of their world. But when it comes to top predators, there are many other fascinating case studies, some hailing from parts of the planet we're much less familiar with.
Ocean PredatorsIn the remote Southern Ocean that encircles Antarctica, sperm whales reign supreme. The largest toothed predator on the planet, a sperm whale can reach lengths of up to 52 feet and plunge to depths of 2,250 meters to hunt giant squid. But more than just powerful hunters, sperm whales are a critical sources of fertilizer. Or, at least, their excrement is.
Of course, it'd be unfair to talk about critical ocean predators without mentioning sharks. To get the scoop on Earth's most iconic toothy fish, I spoke with University of Miami marine ecologist David Shiffman, a shark advocate who also writes at Southern Fried Science. Sharks, it turns out, can also wear many different hats in an ecosystem. For instance, in addition to being skilled hunters, some sharks are professional fear-mongers.
"The most common way people think of sharks influencing the food web is by eating other animals," Shiffman told me. "But a lot of research has shown that the bigger way sharks make an impact is by influencing the behavior of their prey." Basically, they convince creatures in the rest of the ocean to stay the hell away.
"The presence of tiger sharks can influence the behavior of dolphins, sea turtles, fish, even birds," Shiffman said. "And if the areas that herbivores forage are dictated by sharks, this can influence the whole food web." Indeed, ongoing studies at the Shark Bay Ecosystem Research Project are showing how shark avoidance can indirectly impact the structure of the marine seagrass beds, which form the physical architecture of the ecosystem.
An Uncertain Future
Of the 31 largest mammals in the order Carnivora—a list which includes wolves, giant cats, bears and hyenas—61 percent are listed as threatened by the International Union for the Conservation of Nature. Seventy seven percent are in decline. Writing in Science on how the disappearance of top carnivores may affect ecosystems worldwide, a group of environmental scientists state that "we should expect surprises, because we have only just begun to understand the influences of these animals on the fabric of nature."
Included among those surprise impacts is how the loss of Earth's top carnivores may affect us.Earth's largest predators have inspired our stories, mythologies and artwork since the dawn of culture. Losing them is more than a loss to the environment—it's a loss to humanity.
source: gizmodo.com by Maddie Stone