Benefits of large animals spreading nutrients across the world are reduced by declining populations.
Once upon a time, large animals roamed the face of the Earth and, as one can imagine, deposited vast amounts of feces and waste wherever they happened to be at the time.
A newly-published report, cited on washingtonpost.com, is saying the loss of the large animals and their poop, is causing a reduction of the spread of vital nutrients around the globe.
The research looked at models of the distribution of phosphorus, which is a necessary nutrient for plant growth. Animals of all sizes spread these vital nutrients around by eating and then moving to a different area when the excrete waste materials. If not for the transportation of these nutrients by the creatures, the nutrients would simply fall to the ground and be washed away with the rain, winding up eventually on the floor of the ocean.
Take the whales for an example. They feed in the deep waters of the ocean, and when they come up to the surface to breathe, they poop as well, spreading nutrients near the surface for other organisms, thus doing a kind of re-cycle of the nutrients.
A dramatic loss in the whale population in the last few centuries has brought about a sharp drop in the amount of phosphorus that is being re-cycled. Researchers estimate that in prior centuries, the whales returned some 750 million pounds of phosphorus to the surface every year, but in today’s world, they are only returning about 165 million pounds, just 23 percent of the previous amount.
The researchers also estimated that birds and fish that eat in the oceans and return to land areas to poop, are only bring back about 4 percent of their previous amounts.
Chris Doughty of Oxford University and lead author on the study, said, “Large free-ranging animals are much less abundant than they once were. Today, if scientists were to study the role of animals they would find that it is important but small.”
He further explained, “However, in the past, we hypothesize that it would have been at least an order of magnitude larger than today. Essentially, we have replaced wild free-roaming animals with fenced domestic cattle that cannot move nutrients in the same way.”
The scientists warn that we could see easily accessible phosphorus disappear in as little as 50 years, if conditions remain the same. A push for conservation and recovery of whales and other large animals could make a change in the future.
The results of the study were published in the Proceedings of the National Academy of Sciences.