Loss of Poop From Giant Animals Disrupting Earth's Nutrient Cycle

Posted on October 27, 2015

Graphic showing reduction in poop from giant animals

Earth used to be home to millions of enormous animals. These large creatures like truck-sized sloths and ten-ton mammoths deposited enormous quantities of poop. The declines and extinction of large animals has led to a great reduction in the amount of waste which has harmed Earth's nutrient cycle say researchers from the University of Vermont and University of Oxford.

Joe Roman, a biologist at the University of Vermont and co-author on the new study, says in a statement, "This broken global cycle may weaken ecosystem health, fisheries, and agriculture."

The reduction in large animals on Earth has occurred not just on land but in the oceans as well. There are less huge whales than there once were. The scientists say whale densities are estimated to have declined by as much as 90% over the last three centuries due to commercial hunting. 350,000 blue whales - some weighing over 100 tons - used to inhabit our oceans and now there are just a few thousand. The researchers say the capacity of these marine mammals to move the vital nutrient phosphorous from deep ocean waters to the surface has dropped by 75%. The new study challenges theories that microbes are the only crucial part of the ecosystem.

Joe Roman, a whale expert in UVM's Rubenstein School of Environment and Natural Resources, says in a statement, "This study challenges the bottom-up bias that some scientists have - that microbes are running the show, and phytoplankton and plants are all that matter. This once was a world that had ten times more whales; twenty times more anadromous fish, like salmon; double the number of seabirds; and ten times more large herbivores - giant sloths and mastodons and mammoths."

The researchers say poop from big farm animals is not fixing the broken cycle primarily because they are fenced in which constrains their movements and the release of their nutrients. Ideas that could help restore the damaged nutrient pathway on Earth include allowing the whale population to flourish and bringing back herds of large roaming creatures like bison to North America.

A research paper on the study can be found here in the journal, Proceedings of the National Academy of Sciences..

Image: NAS; design by Renate Helmiss