In recent decades, Lyme disease, a tickborne illness found across North America, has been on the upswing, with some areas seeing a percent rise in disease incidence. A study which 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.
In 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, 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. After consuming prey at depth, sperm whales return to the surface to spew out iron-rich plumes of defecant.
These so-called "poo-namis" are like Miracle Grow for phytoplankton, the photosynthetic microbes that collectively account for 50 percent of the carbon drawn out of our atmosphere every year. A study published in the Proceedings of the Royal Society B found that these sperm whale shit-storms are responsible for roughly thousand tons of carbon sequestration in the deep ocean every year.
Two hundred thousand tons—all thanks to excrement. Before industrial whaling dramatically shrank sperm whale populations, that carbon sink could have been up to ten times greater. 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. Juvenile tiger shark in the Bahamas. That the mere presence of sharks can dictate where other organisms spend their time is a relatively new discovery, one whose implications ecologists are still grappling with.
The phenomena has been well documented in Shark Bay , Australia; that region is home to one of our planet's largest populations tiger sharks , an apex predator that can grow to be 16 feet long and weigh up to 1, pounds. The Siberian tiger is among the most threatened of Earth's large cats. There are plenty of other predators with well-documented ecological impacts, aside from the handful I've discussed here.
Both the science of ecology and our obligations to minimize harm to nature require that land use and conservation policies reflect this higher standard. For definitions of predator-related terms, see our Predator Glossary. NOTE: Additional information on ecosystem services, including economic benefits, is coming soon.
Perturbations to trophic interactions and the stability of complex food webs. PNAS , August 11, , vol. Large predators and trophic cascades in terrestrial ecosystems of the western United States. Biological Conservation Effects of predator functional diversity on grassland ecosystem function. Ecology , 90 9 , , pp. Does interference competition with wolves limit the distribution and abundance of coyotes?
Journal of Animal Ecology 76, — Gese, J. Ecology , 89 3 , , pp. Slater, C. The Condor — Caro, D. Brown, B. Clucas, J. Hunter, J. Ketchum, K. McHugh, F. Conservation Biology Vol. Linking a cougar decline, trophic cascade, and catastrophic regime shift in Zion National Park. Zavaleta, V. Eviner, R. Naylor, P. Vitousek, H. Extirpation of great sharks along the eastern seaboard caused an irruption of rays and the collapse of a century-old scallop fishery, a glimpse of the future as shark populations crash worldwide.
Overfishing of cod, a top predator of lobster and sea urchins, upended the coastal North Atlantic, producing hyper-abundant lobster and a market glut in the Gulf of Maine, as well as an urchin boom-and-bust cycle off Nova Scotia, where urchins have been periodically wiped out by disease. Where was that evidence? Designing experiments to reveal cascades on land, across large-scales and over long time periods, seemed nearly impossible.
Long-term trials teasing out wide-ranging interactions among predators and other species promised to be unwieldy and expensive. Nonetheless, startling revelations continued to crop up.
Top predators — jaguar, mountain lion, harpy eagle — fled rising waters. Multiplying out of control, howler monkeys went mad as their numbers soared and the plants they ate increased toxins in self-defense. Some islands were cloaked in thorns as leaf-cutter ants — undeterred by armadillos or other predators — starved the soil of nutrients by carrying every leaf down to their lairs. Yellowstone proved that damage to a terrestrial food web could be reversed and an ecosystem restored with the return of a single species.
It is a sobering lesson for the eastern U. Yet despite such developments, researchers of trophic cascades have despaired of securing the money and means to examine predator removal in large-scale, long-term trials on land.
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