Past VS Present
Scientists claim we are entering the 6th mass extinction. Mass extinctions occur when over 75% of species are lost within a geologically short timespan. Historically, earth has seen five mass extinctions, caused by catastrophic events such as volcanic eruptions or asteroids, that radically change the earth's carbon cycle. With anthropogenic novelty driving contemporary extinctions, humans are responsible for the big killers today (Figure.1). Sadly, species have no respite when human populations are projected to rise from 7.6 billion today to 11.2 billion by 2100. History reveals that an increase in human biomass correlates with a decline in megafauna biomass on Australia, Eurasia and Beringia. Another striking parallel from regional extinctions in the late Pleistocene warns us that human pressures coupled with climate change spells disaster for species in the 21st century. If past events predicate the future, now is the time to act. Unlike the past, we have international organisations like the IUCN and NGOs supported by collaborating scientists, governments and civil society working to support global conservation efforts.
The golden spike of extinctions?
Conceptualising the rate of biodiversity loss over time is taxing. A group of scientists compared current rates of mammal and vertebrate extinctions against highly conservative (A) and conservative (B) estimates of background extinction rates (Figure 2). Assuming the background rate of two mammal extinctions per 10,000 species per 100 years (2 E/MSY), 338 extinctions have been confirmed using population counts (species defined by DNA analysis). A further 30,000 out of the 112,400 species on the IUCN Red List are threatened with extinction.
The average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate.
Extinctions over the past century would have taken 800 to 10,000 years to occur under the background rate of 2 E/MSY. In Leiman's terms, extinctions have rapidly increased since the industrial revolution (Figure 2).
Scientists acknowledge the limits of recording taxa and species extinction. In the same way that measuring rates of speciation and extinction is much harder for invertebrates, fish, reptiles and plants. The assessment of current extinctions is based on the IUCN's record of species; accounting for unnamed species could result in much higher rates.
The path forwards...
Life on earth for non-human species looks bleak. Neither are we invincible. Ironically, we depend on the very ecosystems that we are over-exploiting and driving into extinction. Declining species diversity erodes ecosystem services and critical natural capital. However, rescuing existing species does not guarantee survival into the future because genetic diversity within species populations matters. Without a diverse gene pool, interbreeding occurs, causing poor health. We will touch upon functional diversity and keystone species in later posts.
However, not all hope is lost. To suggest that species loss is irreversible would be misleading. Over 99% of organisms to have ever existed are now extinct. New species evolve to fit ecological niches, evident from the Cretaceous period. The last mass extinction obliterated the non-avian dinosaurs, which paved the way for the evolution and diversification of mammals and birds. Nature has an immense power to recover, the caveat... without destructive human behaviours.
The pill to cure the current extinction epidemic? Stop engaging in the big killers.
...................................... Until next time! .....................................
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