Wildlife populations around the world have plummeted by more than half in less than a half-century, according to a major study by one of the world's biggest environmental groups.
The Swiss-based WWF's "Living Planet Report 2014" notes the sharp decline in biodiversity comes with human "demands on nature...unsustainable and increasing."
The flagship study "measures more than 10,000 representative populations of mammals, birds, reptiles, amphibians, and fish."
The 52-percent drop in the number of vertebrates is a far bleaker assessment than even two years ago, the group says, due to improved methods of measuring animal populations.
"Biodiversity is declining in both temperate and tropical regions, but the decline is greater in the tropics," it says.
Some of the worst of the newly discovered animal losses are in South America, WWF adds.
Continued losses and deterioration of natural habitats are compounded by pressures from hunting and fishing and represent the chief threats to wildlife populations around the world, it says. Other primary factors are global warming, invasive species, pollution, and disease.
The group's primary barometer, the Living Planet Index (LPI), shows terrestrial species declining by an average of 39 percent, freshwater species by 76 percent, and marine species by 39 percent.
We "may have already crossed 'planetary boundaries' that could lead to abrupt or irreversible environmental changes," WWF Director General Marco Lambertini warns in the report's foreword.
"We are using nature's gifts as if we had more than just one Earth at our disposal," he says.
The report challenges countries "with a high level of human development" to "keep their [ecological] footprint down to globally sustainable levels."
It cautions that "we must work to ensure that the upcoming generation can seize the opportunity that we have so far failed to grasp, to close this destructive chapter in our history, and build a future where people can live and prosper in harmony with nature."