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Nutrient Deficiencies in Amazon Caused by Mass Extinctions

By Frontiergap @FrontierGap

It is not news to scientists that there is a lack of phosphorous in parts of the Amazon Rainforest, which is essential for mineral and plant growth. Now, a new study in Nature Geoscience posits a reason for this lack: the mass and rapid extinction of large mammals.

Nutrient deficiencies in Amazon caused by mass extinctions

Picture courtesy of Nils Rinaldi

The Amazon was once the home of the sloth, the rhino like creatures called toxodons, and the fantastically armoured glyptodons. By 10,000 B.C however, these mega fauna were largely extinct, possibly due to overhunting by man or climatic changes. It is now considered that the extinction of these animals has caused this nutrient deficiency, particularly the lack of nitrogen, in parts of the Amazon. Mammals are primary dispensers of nutrients, in their feces, urine and through their decomposition at death. Field research shows that larger mammals (such as elephants) not only give off larger quantities of these vital nutrients, but also spread them over larger distances.

So, it makes sense that the removal of South America’s largest mammals from the environment could still be impacting on the nutrients within the Amazon today. 70 percent of the animals that faced extinction were over 10 kilograms, therefore the Amazon lost its vessel by which to disperse nutrients far and wide, and this has played a large role in the history of Amazonia. Slash-and-burn farming  practices are now used due to the lack of necessary nutrients for long term crop production, for example.

A team of researchers from the UK and US developed a mathematical model in order to calculate the impact of this sudden loss of megafauna (animals with a body mass greater than 44kg). The results showed that the extinctions were responsible for a staggering 98 percent reduction in the dispersal of phosphorus. "Large animals play a disproportionately important role in this translocation of nutrients because they travel farther and have longer food passage times than smaller animals," say the researchers. Today, however, the majority of nutrient dispersal in the Amazon is through abiotic factors, which means the rivers and air. Therefore, nutrients become concentrated in just a few places, rather than spread far and wide.
Human impact on the health of the Amazon stretches further back than originally considered. "To the extent humans contributed to the megafaunal extinctions, this suggests that major human impacts on global biogeochemical cycles stretch back to well before the dawn of agriculture," the researchers write. However, megafauna extinctions did not end twelve thousand years ago. Great numbers of the worlds large mammals are in decline and some are even on the edge of extinction, which could bring another bout of nutrient deficiency in parts of Africa and Asia. 

By Camilla James

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