[P]revious experiments conducted in Kenya have isolated patches of land from megafauna such as zebras, giraffes and elephants, and observed how an ecosystem reacts to the removal of its largest species. Rather quickly, these areas become overwhelmed with rodents. Grass and shrubs increase and the rate of soil compaction decreases. Seeds and shelter become more easily available, and the risk of predation drops.Vertebrates aren't the only species on a troubling path of defaunation. Over the last 35 years, while the human population has doubled, invertebrate numbers have plummeted by 45 percent.
Consequently, the number of rodents doubles -- and so does the abundance of the disease-carrying ectoparasites that they harbor.
"Where human density is high, you get high rates of defaunation, high incidence of rodents, and thus high levels of pathogens, which increases the risks of disease transmission," said Dirzo, who is also a senior fellow at the Stanford Woods Institute for the Environment. "Who would have thought that just defaunation would have all these dramatic consequences? But it can be a vicious circle."
Past mass extinctions were driven by planetary transformations or catastrophes, but the extinction we face today can be attributed to man-made causes.
This is far from the first time that scientists have cautioned us of the next looming mass extinction. Last month, The Week delivered a similar warning that we could be headed the way of the dinosaurs if we don't address these crises immediately. In February, NPR concluded the mass extinction is already underway.
In the words of Neil deGrasse Tyson:
We just can't seem to break our addiction to the kinds of fuel that will bring back a climate last seen by the dinosaurs, a climate that will drown our coastal cities and wreak havoc on the environment and our ability to feed ourselves. All the while, the glorious sun pours immaculate, free energy down upon us, more than we will ever need. Why can't we summon the ingenuity and courage of the generations that came before us? The dinosaurs never saw that asteroid coming. What's our excuse?