There are two main causes of loss of wildlife. The first is habitat loss and degradation, "like converting a tropical lowland forest to an oil palm plantation," Loucks said. "The second thing is poaching, or in the case of marine systems, overfishing. Those are the largest drivers of population decline."
Who's most at risk
Animals whose populations are decimated because of incessant demand for wildlife products, like ivory, in places like southeast Asia, are high at risk. "So that's elephants, pangolins, sharks for shark fin soup," Loucks said.
But it doesn't stop there.
"The species who require freshwater to survive have declined 81 percent in just over 40 years," Loucks said, citing "overexploitation, pollution, dams, invasive species and climate change" as the main drivers of this drastic drop.