Extinctions of Large Animals Sever the Earth's 'Nutrient Arteries'

A new study has demonstrated that large animals have acted as carriers of key nutrients to plants and animals over thousands of years and on continental scales.

The paper in the advance online publication of the journal Nature Geoscience explains that vital nutrients are contained in the dung and bodies of big animals. As they eat and move more than small animals, they have a particularly important role in transporting nutrients into areas where the soil is otherwise infertile.

In the study, the researchers use a new mathematical model to calculate the effect of mass extinctions of big animals around 12,000 years ago, focusing on a case study of the Amazon forest. They estimate that extinctions back then reduced the dispersal of phosphorus in the Amazon by 98%, with far-reaching environmental consequences that remain to this day. The model also enables them to forecast the likely environmental effects of the extinction of large animals currently under threat in Africa and Asian forests.

Up until 12,000 years ago, much of the world looked like an African savannah. For instance, South America was teeming with large animals, described by scientists as ‘megafauna’ — a term for animals with a body mass of more than 44kg (the size of a large dog). These megafauna in South America, which overlapped with the earliest humans, included several species of elephant-like creatures, giant ground sloths, and armadillo-like creatures the size of a small car. In South America, most nutrients originate in the Andes mountain range and are washed into the forests through the river system. However, on dry land, these nutrients are in short supply unless they are transported through animal dung and bodies. While small animals distribute nutrients over small distances, large animals have a much greater range. According to the study, the extinctions of large animals 12,000 years ago wiped out one of the main means of transporting nutrients far from the rivers creating a nutrient deficiency which continues to affect plant and animal life in parts of the region today.

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Extinctions of Large Animals Sever the Earth's 'Nutrient Arteries'