Mammals under threat: 2nd extinction wave underway in Australia, Caribbean

New study predicts 558 species of mammals to be extinct by turn of century
The Black-flanked Rock Wallaby, an endangered Australian mammal. Photo: Wikimedia Commons
The Black-flanked Rock Wallaby, an endangered Australian mammal. Photo: Wikimedia Commons

Australia and the Caribbean are already in the middle of a ‘second wave’ of mammalian extinctions, a new study has claimed, while predicting that the world would see 558 mammalian extinctions by 2100.

“By the year 2100, we predict all areas of the world to have entered a second wave of extinctions. Our simulation results indicate that this additional wave of anthropogenic extinctions may be much greater than the currently increased rates, by several orders of magnitude,” the authors of the study said.

The study The past and future human impact on mammalian diversity was published on September 4, 2020, in Science Advances.

The authors said “when accounting for the current threat level of species, we predict 558 extinctions. This pattern is reflected in all analysed subsets of the data and is particularly large for Africa, the Americas and Eurasia, since current extinction rates for these continents are still at a comparatively moderate level, yet many species are severely endangered.”

The study has also noted that human influence, rather than climate was a much more likely cause of earlier extinctions.

Tday, there are approximately 5,700 extant mammal species, the researchers noted. They added that at least 351 mammal species had gone extinct since the beginning of the Late Pleistocene 126,000 years ago, 80 of which were known from historical reports since the year 1500 CE, while all others are only known from fossil or zooarcheological records

The researchers found that the timing of human arrival in continents like the Americas and Australia as well as island systems like Madagascar and the Caribbean coincided sharply with mammalian extinctions.

In Australia, human arrival first occurred between 65,000 and 44,000 years ago. In North America, humans (‘Paleo Indians’) first came between 21,000 and 11,000 years ago.

For South America, the timing was between 35,000 and 8,000 years ago. In Madagascar, they came between 10,000 and 4,000 years ago and between 7,000 and 4,000 years in the Caribbean.

The scientists noted their findings were consistent with older studies according to which, “mammals in Africa and Eurasia were ecologically adapted to predation by hominins through co-evolution, possibly dating back as far as several million years ago and were thus more resilient to human hunting pressure in the late Quaternary, leading to fewer extinctions”. This though, was not the case with the Americas and Australia.

Human population density, as a single predictor, explained mammalian extinction patterns with 96 per cent accuracy, the scientists wrote. Similarly, human land occupation predicted past extinctions with 97.1 per cent accuracy.

On the other hand, climate predictors, led to low accuracy values, such as global temperature with 63.6 per cent accuracy and the rate of temperature change with 60.2 per cent accuracy.

The researchers accepted that explaining extinctions with a single variable such as human population density was over-simplification. However, they expected their results to hold.

“Our results show that human population density has substantial predictive power over the process, probably because it is correlated with other anthropogenic factors such as more intensive hunting pressure, land use, ecosystem modifications, for example, through the use of fire and several cascading effects that result from human impact on the natural world,” they noted.

They also said their conclusions regarding climatic factors would also be viewed as over simplistic.

“Our correlation models are not affected by absolute temperature values, which certainly differ between regions,” they wrote.

“Instead, they assume that extinction rates around the globe follow relative trends in the data, which we expect to be shared by all regions. Therefore, we expect our findings of low adequacy of climatic correlation models to hold true in general, even if more regionally detailed paleoclimate data were available and applied in these models,” the researchers added.

Related Stories

No stories found.
Down To Earth