When megafauna disappear, so does their poop- disrupts Earth’s nutrient cycleLeave a Comment
This diagram shows an interlinked system of animals that carry nutrients from ocean depths to deep inland — through their poop, urine, and, upon death, decomposing bodies. A new study in the Proceedings of the National Academy of Sciences reports that — in the past–this chain of whales, seabirds, migratory fish and large land mammals transported far greater amounts of nutrients than they do today. Here, the red arrows show the estimated amounts of phosphorus and other nutrients that were moved or diffused historically — and how much these flows have been reduced today. Grey animals represent extinct or reduced densities of animal populations. Credit: Diagram from PNAS; designed by Renate Helmiss
Posted: 26 Oct 2015 02:20 PM PDT
In the past, whales, giant land mammals, and other animals played a vital role in keeping the planet fertile by transporting nutrients via their feces. However, massive declines and extinctions of many of these animals has deeply damaged this planetary nutrient recycling system, threatening fisheries and ecosystems on land, a team of scientists reports.
Giants once roamed the earth. Oceans teemed with ninety-foot-long whales. Huge land animals–like truck-sized sloths and ten-ton mammoths–ate vast quantities of food, and, yes, deposited vast quantities of poop.
A new study shows that these whales and outsized land mammals–as well as seabirds and migrating fish–played a vital role in keeping the planet fertile by transporting nutrients from ocean depths and spreading them across seas, up rivers, and deep inland, even to mountaintops.
However, massive declines and extinctions of many of these animals has deeply damaged this planetary nutrient recycling system, a team of scientists reported October 26 in the Proceedings of the National Academy of Sciences.
“This broken global cycle may weaken ecosystem health, fisheries, and agriculture,” says Joe Roman, a biologist at the University of Vermont and co-author on the new study.
On land, the capacity of animals to carry nutrients away from concentrated “hotspots,” the team writes, has plummeted to eight percent of what it was in the past–before the extinction of some 150 species of mammal “megafauna” at the end of the last ice age.
And, largely because of human hunting over the last few centuries, the capacity of whales, and other marine mammals, to move one vital nutrient–phosphorus–from deep ocean waters to the surface has been reduced by more than seventy-five percent, the new study shows….
The world of giants came to an end on land after the megafauna extinctions that began some 12,000 years ago–driven by a complex array of forces including climate change and Neolithic hunters. And it ended in the oceans in the wake of whale and other mammal hunting in the industrial era of humans.
“But recovery is possible and important,” says UVM’s Roman. He points to bison as an example. “That’s achievable. It might be a challenge policy-wise, but it’s certainly within our power to bring back herds of bison to North America. That’s one way we could restore an essential nutrient pathway.”
And many whale and marine mammal populations are also recovering, Roman notes. “We can imagine a world with relatively abundant whale populations again,” he says.
But have domestic animals, like cows, taken over the nutrient distribution role of now-extinct large land animals? No, the new study shows. Though there are many cows, fences constrain the movement of domestic animals and their nutrients. “Future pastures could be set up with fewer fences and with a wider range of species,” the team writes….
Christopher E. Doughty, Joe Roman, Søren Faurby, Adam Wolf, Alifa Haque, Elisabeth S. Bakker, Yadvinder Malhi, John B. Dunning Jr., and Jens-Christian Svenning. Global nutrient transport in a world of giants. PNAS, October 26, 2015 DOI: 10.1073/pnas.1502549112
Francois Gohler/Science Source
26 October 2015 5:45 pm Science Mag
Humans have been bad for blue whales. As many as 350,000 of the giant mammals (pictured) once plied the oceans; now, only a few thousand are left.
Although removing such creatures from ecosystems can have a host of effects, a new study draws attention to one in particular: There’s a lot less poop getting spread around the planet. In the research, published online today in the Proceedings of the National Academy of Sciences, the scientists describe how losing these animals and other “megafauna” has upset a global cycle that once passed large amounts of nutrients like phosphorus from the ocean depths where large marine mammals like blue whales often feed into the sunlit surface waters where seabirds or migrating fish like salmon browse.
As those fish swam back up the rivers where they were born or the birds returned to dry ground, the nutrients went with them, incorporated into their bodies or excreted, eventually feeding a host of terrestrial organisms. In turn, those animals’ own waste—and eventually decomposing bodies—helped spread the nutrients even further, fertilizing the interior of continents, the scientists say.
In all, the researchers used a set of mathematical models to reveal that today animals only have about 6% of their former capacity to move such nutrients away from “hot spots” and across the oceans and land.
Such a loss may continue to weaken ecosystem health, fisheries, and agriculture, leaving them less naturally productive than they might otherwise be. Protecting whales, migratory fish, and seabirds could make a difference in restoring, at least somewhat, the nutrient pathway, the scientists say.