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Invasive, Indeed One species—Homo sapiens—consumes nearly a quarter of Earth's natural productivity
Sid Perkins, Science News Online
Week of Oct. 13, 2007; Vol. 172, No. 15

Some people live lightly on the land: Bedouin clans roam the deserts of the Middle East and North Africa; small groups of indigenous people follow reindeer herds across frigid Arctic terrain; and tribes of hunter-gatherers forage the plains of southern Africa and the forests of Amazonia and Papua New Guinea.

Then there's the other 6.6 billion of us.

When we farm, clear forests, and build cities, dams, and roads, we dramatically alter the landscape. In some places, we increase the land's productivity—measured as the amount of plant life at the base of the food chain—by adding immense amounts of water and fertilizer. New research indicates that on the whole, however, human presence significantly decreases Earth's biological productivity. For instance, many of today's cities occupy large patches of what had been some of the world's most fertile land.

Of the biological productivity that remains, people are gathering an ever-increasing share, sometimes by boosting their quality of life, but often merely by dint of their burgeoning numbers. In some regions, each spanning millions of square kilometers, human activity consumes almost two-thirds of the biological productivity that would otherwise be available.

"We were surprised how intensively these regions were being affected" by human presence, says K. Heinz Erb, an ecologist at Klagenfurt University in Vienna. "Only one-third of the natural productivity is left for all the other species."

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