Last updated April 23, 2018 at 11:12 am
The world’s animals may still be getting smaller, which is not good news and it’s largely our fault.
An African elephant and her baby in Masai Mara at Kenya. Large mammals like this may disappear. Credit: iStock
Humans have been driving a global reduction in terrestrial mammal size for thousands of years and if this trend continues there may be nothing bigger on Earth that the domestic cow in a century or two from now, scientists from the University of New Mexico say.
Notably, they found that there was a particularly striking reduction in size during the late Pleistocene, when humans developed long-range weapons.
The research team led by Professor Felisa Smith looked at distribution and size of mammals for the last 66 million years.
Mammal extinction
It found a substantial bias in mammal extinction during the periods when humans were dispersing around the globe, whereby species that went extinct tended to be two to three times bigger than mammals that survived, a trend that was evident globally.
Prior to humans’ migration out of Africa 125,000 years ago, Africa was home to mammals of smaller size (with a mean body mass roughly half that of mammals found in Eurasia), which the authors suggest is reflective of the hominin-mammal interactions that had already been at play.
The authors report a greater than 10-fold drop in both mean and maximum body mass of mammals during this time; for example, mean mass of terrestrial mammals in North America fell from 98.0 to 7.6 kg.
If current trends continue, the mean body mass will drop from 7.7 to 4.9 kg in a few hundred years.
As mammals play a critical role in shaping ecosystems, the downsizing trend will have a cascading impact on other organisms.
The paper was published last week in Science.
