Sixth mass extinction will be worse than previously thought, say scientists

The planet’s sixth mass extinction, fuelled by human activities, may trigger a rapid biodiversity imbalance, according to scientists.

The researchers analysed more than 71,000 animal species from five strata, including mammals, birds, reptiles, amphibians and insects and found that the next mass extinction will be worse than previously thought.

With biodiversity declines greatly exceeding the levels of increase, nearly 50 per cent of the animal population across all strata is being driven towards extinction — and eventually towards mass extinction — noted the findings of their study published in Biological Reviews of the Cambridge Philosophical Society.

Mass extinction occurs when 75 per cent of the world’s species collapses in less than 2.8 million years.

Also read: Good while it lasted - I: 6th mass extinction underway, courtesy humans

The research titled More losers than winners: Investigating Anthropocene Defaunation through the Diversity of population trends signals that global biodiversity is entering a mass extinction phase. Ecosystem heterogeneity and functioning, biodiversity persistence and human well-being are under increasing threat, the authors noted.

The study offers the first comprehensive global scale picture of four categories of trends — decreasing, stable, increasing and species for which they remain unknown (for vertebrates and insects) — sourcing data from the International Union for Conservation of Nature (IUCN) Red List.

The analysis portrayed a widespread global erosion of species, with 48 per cent undergoing declines, while 49 per cent remain stable and 3 per cent of species currently increasing.

Around 33 per cent of the species currently categorised as ‘non-threatened’ by the IUCN Red List show a declining trend. The declining population pattern indicates an imminent extinction, they added.

Extinction threat is particularly severe for amphibians compared to others and the decline was higher in the tropical regions than temperate. The proportion of unknown trends is highest in insects (75 per cent),  followed by 74 per cent among fishes, it added. 

Meanwhile, most species among reptiles and fish are showing stable growth trends. Amphibians with the highest proportion of decreasing populations (63 per cent) also have the lowest proportions of stable population at 37 per cent.

The mammals with declining populations were estimated to be 56 per cent. Birds were reported to have the highest proportion of increasing population (at six per cent) and mammals and fish are experiencing a population growth of just two per cent. 

Among vertebrates, the stable species population stood highest among reptiles at 70 per cent, followed by fish at 58 per cent. But a decrease of 28 per cent is observed among the reptile population and 41 per cent in fish.

Also read: As we fight to protect species on the brink of extinction, let’s not forget the familiar ones

While comparing solely terrestrial, marine or freshwater habitats, vertebrates have a declining population pattern (47 per cent). And freshwater and marine species have a declining pattern of 45 per cent and 36 per cent, respectively.

The researchers further revealed that the available limited information shows that the insect population is dropping at a rate of 54 per cent, with just two per cent undergoing population growth. 

Compared to the three habitats, the proportion of terrestrial species shows a declining trend at 66 per cent, far beyond the freshwater species, at 12 per cent. 

The researchers estimated that “around 40 per cent of global species many become extinct in coming decades”.

The scientists, however, claimed that limited focus on IUCN Red List threatened categories can lead to a risk of underestimating severe biodiversity loss. They estimated that considering the ongoing and unabated population declines for ‘non-threatened’ species, an additional 2,136 species could be further threatened.

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