University Life: Why we’re living in the shadows of lost giants

Lecturer in Ecosystem Ecology within the Environmental Change Institute (ECI) at the University of Oxford

We live in the shadows of lost giants. Until relatively recently almost every plot of land on this planet was teeming with huge animals, the sort we associate with African game parks today.

Researchers at Oxford University are looking at how the Earth’s ecological system and even the climate is affected by their disappearance. The numbers are astounding.

For instance, when people first arrived in South America, there were more than 60 species of animals larger than the current largest animal, the Tapir: all now extinct.

Just imagine a world of Giant sloths, car-sized glyptodonts in the Americas, rhino-sized marsupials in Australia, and gorilla-sized lemurs in Madagascar.

Over the last 50,000 years, a blink of an eye in geological and evolutionary time, these giants disappeared or were greatly reduced in number – and guess what, modern humans seem to be mainly to blame.

One theory is that as they spread through the planet, humans started to hunt these creatures, leading to mass extinctions in many cases.

Scientists around the world have written about the size and cause of this decline but only now are we beginning to realise their legacy in the health of our soil, plants and trees.

For instance, the big beasts were able to travel huge distances acting like great big muck spreaders. The smaller animals today just can’t get around the same way.

Their manure carried good soil nutrients like nitrogen and phosphorus, which is one of the main components in fertilizer in agriculture today.

When the animals died, their bodies released more nutrients into the soil.

The whales that fed in the depth of the ocean would surface to defecate and from there seabirds and fish that swam in both oceans and rivers would transport the phosphorous released by the whales inland.

This system is especially important because it goes against gravity and rescues nutrients that would otherwise have fallen to the bottom of the ocean.

This recycling system has been largely stopped.

Our research found that animals now only transport about six per cent of the nutrients on land and in the sea compared with before mass extinctions and population declines.

Phosphorus recycling will become increasingly important in the future as easily accessible mined phosphorus could run out in as little as 50 years.

Restoring the natural system of recycling that the Earth once had by increasing free ranging animal populations, especially in the oceans, river and air, could go a long way towards increasing phosphorus concentration on land.

Even the wildest landscapes in the corners of the Earth are missing these giants known as megafauna.

The consequences of the decline in the megafauna may be felt for centuries or millennia to come.

Our improved understanding of the many ways that they have influenced ecology and biogeochemistry may also help identify the underappreciated service they provided to our planet.

It shows us the important role played by elephants and whale species, as well as seabird and anadromous fish (that inhabit the sea and rivers).

It forces us to ask searching questions about how these species might be allowed to recover.

Global declines in whale populations alone are 66 per cent to 90 per cent of what they were just 300 years ago.

Last year in Oxford we had a major international workshop at St John’s College Oxford, supported by the Oxford Martin School, which gathered experts from paleoecology and anthropology through to conservation science and policy.

This was the first international meeting to ponder on the effects of these giants.

We examined the potential and consequences for bringing them back in particular landscapes and this important meeting has resulted in two special features published this week in top scientific journals, Proceedings of the National Academy of Sciences and Ecography.

Next time you are at Cotswold Wildlife Park, just imagine how larger versions of animals housed there today could have been roaming down what is now Burford High Street.

What a thought!