Extinction of big animals sever Earth's 'nutrient arteries'

The mass extinction of big animals in the Amazon region 12,000 years ago is behind loss of soil nutrients today, Oxford scientists say, warning of further damage if gigantic creatures like elephants disappear.
Thousands of years after human hunters wiped out big land animals like giant ground sloths, the ecosystems they lived in are still feeling the effects, researchers said.
Researchers demonstrated that large animals have acted as carriers of key nutrients to plants and animals over thousands of years and on continental scales.
The study 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.
Researchers used 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 per cent, with far-reaching environmental consequences that remain to this day.
The model also enabled 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.
These megafauna, which overlapped with the earliest humans, included several species of elephant-like creatures, giant ground sloths, and armadillo-like creatures.
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, researchers said.

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.
The researchers have developed a mathematical model to estimate the ability of animals to distribute nutrients.
This model can estimate the effects of past extinctions, such as those in the Amazon. It can also forecast the effects of potential events thousands of years in the future, such as calculating how much the fertility levels of the soil would fall following elephant extinction in Africa.

The study finds that the effect of the mass extinction of megafauna 12,000 years ago was to switch off a nutrient pump - vital nutrients, such as phosphorus, were no longer spread around the region but became concentrated in those areas bordering the floodplains and other fertile areas.