In 200 years, cows could become the largest mammals on land, thanks to the devastating effects of human-caused extinctions.
The loss of mammal biodiversity has been a long-term trend continuing for the past 125,000 years at least, and a study by The University of New Mexico in the US shows that this was the fault of human activity.
HOW DID HUMANS CAUSE EXTINCTIONS OF LARGE MAMMALS?
Since the time humans evolved and started to migrate out of Africa, there has been a gradual wave of extinctions of large land mammals.
This has been steadily increasing in intensity across all continents since the time ancient humans such as the Neanderthals and other hominin species started to migrate out of the dark continent into other parts of the world.
The study shows that the decline in the large mammal species follows the global expansion of hominins over the late-Quaternary period, including the Pleistocene and Holocene periods.
Species of giant mammals that died off because of human activity includes the woolly rhinoceros, mammoths, llamas, camels and giant ground sloths as well as ferocious predators such as the short-faced bear, and the scimitar and saber-toothed cats.
HOW HUMANS AFFECTED MAMMAL BODY SIZE
However, humans started to affect the size of mammals much before they left Africa. The study published in Science journal is the first ever which shows that mammals didn’t shrink in size due to an evolutionary process, but rather due to the effect of human activity.
The study found proof that even 125,000 years ago, the size of the mammals in Africa — where humans are believed to have originated and evolved — was actually 50 per cent smaller than in other continents.
The findings are all the more shocking because records show that typically, larger land masses such as Africa are able to support larger mammals.
The researchers showed that body-size downgrading — the loss of the largest species on each continent over time — is a hallmark of human activity, both in the past and present. It looks like we had started to affect mammal diversity and body size even in the ancient period of the late-Pleistocene era.
If this trend continues, we might face a bleak future where larger land animals like elephants, giraffes and hippos will all be gone. The largest terrestrial mammal in 200 years will be the domestic cows, warn the researchers.
HOW DOES CLIMATE CHANGE AFFECT EXTINCTION RISK?
The researchers also examined the potential influence of climate on extinction risk and selectivity over time.
They found that for 65 million years, changes in climate did not result in more extinctions, nor was there a greater tendency for large-bodied mammals to go extinct.
“We suspect that in the past, shifts in climate led to adaptation and movement of animals, not extinction,” said the co-author of the study Jonathan L Payne.
“Of course, today ongoing climate change may result in extinction since most megafauna are limited in how far they can move,” Payne said.