The world relies on the nutrient transfer from animal feces to remain fertile, but new research suggest major species declines and extinctions have put this planetary nutrient recycling system in jeopardy.

The weakening of this vital system could have a negative impact on ecosystem health, fisheries, and agriculture, the University of Vermont reported. The researchers calculated the capacity for land animals to carry nutrients away from "hotspots" has fallen to eight percent of what it was at the end of the last ice age. The capacity of whales, and other marine mammals to carry nutrients such as phosphorous from the deep sea to more shallow waters has been reduced by about 75 percent.

In the past animals were not believed to be vital for nutrient transfer, but this new research demonstrates the animals are crucial for the "distribution pump" of fecal matter that fertilizes naturally barren areas. The loss of these fertilized ecosystems could in turn hurt humans. The researchers pointed out that restoring whale populations could increase the ocean's ability to absorb carbon dioxide and help reduce global warming.

"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," said Joe Roman, a whale expert in UVM's Rubenstein School of Environment and Natural Resources and the Gund Institute for Ecological Economics. "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."

Before modern humans existed animals such as elephant-like gomphotheres that could ingest and distribute large quantities of plant matter. Since this time, the planetary pump may have dropped to just six percent of its former capacity to spread nutrients across both the land and sea. The researchers believe despite their grim findings, recovery is possible. Especially if attention is turned towards animals crucial for nutrient transfer, such as bison.

"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," Roman said.

The findings were published in a recent edition of the journal Proceedings of the National Academy of Sciences.