Large Animal Extinctions Sever Earth's 'Nutrient Arteries' in the Amazon

Large animals play a more important role in our ecosystems than we once thought. Scientists have discovered that these creatures have acted as carriers of key nutrients to plants and animals over thousands of years. Yet as these species become extinct, they could sever the Earth's "nutrient arteries."

Large animals play the role of predators, gobbling down vital nutrients in the form of smaller animals. They carry these nutrients around in their bodies, spreading them with their dung. In fact, they have a particularly important role in spreading nutrients to areas where the soil is otherwise infertile. Take, for example, whales that fall to the ocean floor. They provide this otherwise low-nutrient area with a vital resource.

In order to see exactly how important these large animals are, scientists examined a time about 12,000 years ago. Up until then, much of the world looked like an African savannah. South America teemed with large animals, including several species of elephant-like creatures, giant ground sloths and armadillo-like creatures the size of a small car. Yet an extinction event at that time wiped out many of these animals and, in consequence, a way to transport nutrients.

The scientists developed a mathematical model to calculate the effect of mass extinctions of big animals around 12,000 years ago. More specifically, they focused on a case study of the Amazon forest. They were able to estimate that extinctions back then reduced the dispersal of phosphorus in the Amazon by 98 percent. This had far-reaching environmental consequences that probably exist to this day.

"We have developed a model, based on the size of the animal, that enables us to calculate how extinctions affect the fertility of the landscape that species once inhabited," said Christopher Doughty, lead author of the new study, in a news release. "While 12,000 years may be a timescale that is beyond most people's understanding, through this model we show that extinctions back then still affect the health of the planet to this day. Put simply, the bigger the animal, the bigger its role in distributing nutrients that enrich the environment."

The findings reveal the importance of large animals-something that should be taken into account considering climate change today. As environmental conditions fluctuate, large animals such as polar bears, whales and other species are at risk of becoming extinct. If they do, it's likely that our world could drastically change, just as it did 12,000 years ago.

The findings are published in the journal Nature Geoscience.