The phrase ‘mass extinction’ creates images of meteor strikes, exploding volcanoes and the rapid, brutal, destruction of the nonavian dinosaurs in the mind. A number of things may be wrong with this image, no more so than it was a one-off, and that it couldn’t happen again.
Palaeontologists have deciphered from the rock record that five mass extinctions have occurred throughout the Earths history. These extinctions, known as the ‘Big Five’, are characterised by a loss of over 75% of estimated species over a geologically short period of time, typically in 2 million years or less. They occurred at the end of the Ordovician (439ma), Devonian (364ma), Permian (251ma), Triassic (200ma) and Cretaceous (65ma) Periods. A recent combination of biological and ecological research now indicates that the sixth mass extinction has begun and that human activity is a likely primary driver.
Throughout Earths history there have been an estimated four billion different species, 99% of which have become extinct. This showcases how extinction is not an uncommon phenomenon, however, it is generally balanced by speciation (the evolution of new species) bar in times of mass extinction, where the rate of extinction outpaces the rate of speciation. This can occur for a number of reasons. The current reasons believed to be primarily responsible for the onset of the sixth mass extinction are the fragmentation of habitats, the spreading of pathogens, the introduction of non-native species, climate change, and the direct killing of certain species, all of which are chiefly manifested and somewhat promoted by the effects of anthropogenic activities on Earth. These activities have caused the extinction rate to increase at a rate of 10 – 100 times faster than its baseline average.
Recent news regularly includes stories on the extinction and decimation of a variety of amount of species and populations across the planet, all of which are becoming more commonplace. These extinctions include that of the West African Black Rhino, and the presumed extinction of the Yangtze River Dolphin (Baiji Dolphin). Unfortunately, due to the disparities that exist between the species that are known, and the species that have been discovered but not formally described, the current estimates that indicate that the Earth will be plunged into its next mass extinction in a few centuries are likely to be a serious underestimate. The reality is it that the Holocene extinction event has most likely begun, the recovery of which is on a time scale of millions of years.
Of the many groups of organisms being uncontrollably plunged into the next mass extinction, none are currently being affected more than the amphibians – frog’s salamanders, and caecilians. A detailed worldwide assessment and subsequent updates indicate that at least 33% of the known 6300 species of amphibians are currently threatened with extinction. This trend is only likely to increase as the organisms within these groups are highly adapted, occurring is geographical areas of the tropics and subtropics. As a result, they are the more susceptible to the external pressures of habitat destruction and climate change. A somewhat similar story can be seen in the insect world, where populations are estimated to have dropped by 45% over the last 35 years.
To halt the ever-widening gap being extinction and speciation, which ultimately leads to mass extinction, is not a simple task. Environmental organizations focused on the protection of vulnerable species are continually fighting to prevent the loss of a number of species, in which they often achieve success. However, as one flagship species may be brought back from the cusp of extinction, a plethora of unknown, undiscovered species are subject to annihilation. This unwelcome fact illuminates the notion that no matter how hard a relatively small amount of people try, the effects of the masses is changing the Earth in such a way where little can be done to halt the sixth mass extinction.