A world of mammal diversity has been lost because of humans

On the Serengeti, vast herds of wildebeest, zebra and other herbivores migrate across long distances, trying to avoid being eaten along the way by lions or other species with big teeth and claws. This small section of Africa is one of the last places on Earth to see such a diversity of large mammals, but that isn’t because the region has the perfect climate or abnormally high levels of biodiversity. It’s simply one of the last places where humans haven’t wiped out the megafauna, a new study shows.

Soren Faurby and Jens-Christian Svenning of Aarhus University in Denmark mapped out the current patterns of mammal diversity across the Earth. They then mapped what those patterns would be if humans hadn’t been around for the last 130,000 years or so. The goal was to estimate the natural diversity of mammal species — a key piece of data for studying species diversity and for providing a baseline for conservation efforts. The study appears August 20 in Diversity and Distributions.

The researchers, not surprisingly, found large differences between the diversity of mammals now found across the planet and what it would be if humans had never taken over. But the biggest differences in the hypothetical world were among the megafauna. While there are a few of these large animals left here and there across the globe, there would be a lot more species if we weren’t around.

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In their simulations, when species disappeared differed by location. In some spots, such as Australia and the Americas, most of the mammal losses occurred in prehistoric times. In Africa, losses have mostly occurred during recorded history. And in Europe, it was a bit of both.

Areas of the world that have high plant productivity tended to be home to a lot of natural, though not current, mammal diversity. And today, there is more mammal diversity in mountains. That’s probably because such regions are more difficult for humans to reach and offer animals a refuge, the researchers say.

“The results of the present study exemplify the Anthropocene,” the researchers write, “a human-dominated epoch in which few biological patterns and processes are not substantially modified by humans.” The Anthropocene is also a period that scientists are trying to define, as there is no easy mark in the geologic record for when human influence came to dominate. And for some measures, that influence can go back thousands of years.

So if we are going to conserve a population or species or ecosystem, or we set out to restore it, what should our ultimate goal be? This study and ones like it can help inform conversation by telling us what would be here if we weren’t. But that can’t be the only piece of data that goes into our conservation calculations, because, well, we are here, and whatever else lives on Earth has to live with us, not in our absence.

It can be romantic to think about bringing back the mammoth or letting lions or elephants roam the Great Plains of North America. But we have a rocky history with our attempts to bring back lost species. And placing carnivores in populated places, which might have theoretical benefits to us and the ecosystem, will be a hard sell.

What I take from the new study, though, isn’t guidance for where we should be attempting to restore the past but where we should be focusing efforts to preserve what’s left. If the Serengeti is the last holdout of large mammal diversity, we should be trying our best to keep that from disappearing.