Are humans an invasive species? History holds the answer.

You may have an intense dislike for invasive species like kudzu, but as it turns out, you may be hating on your own kind. Stanford researchers recently found that some populations of early human settlers behaved just like an invasive species—draining the land dry and killing organisms around them.

When humans first arrived in South America, populations grew exponentially and spread across the continent, followed by a population crash—thanks to humans over-consuming local natural resources until they exceeded the area’s carrying capacity for human life. This was followed by a plateau in population growth.

“The question is: Have we overshot Earth’s carrying capacity today?” said senior author Elizabeth Hadly, the Paul S. and Billie Achilles Professor in Environmental Biology and a senior fellow at the Stanford Woods Institute for the Environment in a Stanford statement. “Because humans respond as any other invasive species, the implication is that we are headed for a crash before we stabilize our global population size.”

Did we cause extinctions?

Besides issuing this warning about our global future, the researchers believe this new understanding of human population growth can allow us to better understand how the Pleistocene era’s mass extinction of large mammals like ground sloths and horses occurred, according to the paper, which is published in Nature.

After using radiocarbon dating across more than 1,100 archeological sites in South America, the researchers were able to put together a timeline of human population increases. From this, they discovered two distinct phases of growth on the continent.

The first occurred between 14,000 and 5,500 years ago when humans spread rapidly and grew logistically. Like other invasive species, though, this growth could not be sustained forever. Around 5,500, humans over-exploited natural resources necessary for survival, meaning there wasn’t enough left to sustain the entire human population. Many big animals went extinct when the human population plummetted.

The human population leveled out then, presumably matching up with the region’s carrying capacity. But this doesn’t seem to have lasted long, as the second phase—which went from roughly 5,500 to 2,000 years ago—soon led to exponential population growth.

How did humans in South America suddenly get enough resources to grow in population size? While many would probably consider domestication of animals and crops as the defining impetus, the authors believe this only had a minimal effect. Instead, they argue that the shift towards sedentary societies is the most likely cause. As societies grew more sedentary, humans began practices like intensive agriculture and trade between distant regions, which helped grow the population.

“Thinking about the relationship between humans and our environment, unchecked growth is not a universal hallmark of our history, but a very recent development,” said co-lead author Amy Goldberg, a biology graduate student. “In South America, it was settled societies, not just the stable food sources of agriculture, that profoundly changed how humans interact with and adapt their environment.”

Now, as modern populations continue to boom, this study and others grant both hope and alarm for our future as a species.

“Technological advances, whether they are made of stone or computers, have been critical in helping to shape the world around us up until this point,” said co-lead author Alexis Mychajliw, a graduate student in biology. “That said, it’s unclear if we can invent a way out of planetary carrying capacities.”

—–

Image credit: Thinkstock

The post Are humans an invasive species? History holds the answer. appeared first on Redorbit.

redOrbit.com
offers Science, Space, Technology, Health news, videos, images and reference information. For the latest science news, space news, technology news, health news visit redOrbit.com frequently. Learn something new every day.”