New Study Finds Species In Crisis Are “Clustered”

Photo: Arturo de Frias Marques, Wikimedia CC

A study published last week in the journal Nature provides a new view on the extinction crisis — that most of the planet’s species are not in decline and the ones that are in deep trouble are “clustered.” The study’s lead author, Brian Leung of McGill University in Canada, explained that less than 3% of all species are in free-fall, and when they are removed, “the picture changes dramatically” and indeed, some natural systems “are actually improving, largely in northern and temperate regions.” The areas in trouble are found largely in the Indo-Pacific region, including birds and freshwater mammals. Arctic marine mammals are most at risk. In addition, reptiles in North, Central and South America showed extreme losses.

Why This Matters:  Is the glass half empty or half full? It all depends on how you look at it. These scientists argue that “the way global averages were being estimated could be strongly influenced by a small number of populations that were experiencing extreme declines, even if most were stable.” The news provides some reason for optimism because those natural systems experiencing systematic loss can be prioritized for conservation.  And it also shows that humans are what cause the greatest damage.  

How Did the Authors Count?

The team of researchers from the US and the UK looked at wildlife data from the Living Planet Index, covering more than 14,000 animal populations spanning 57 systems across the world, defined by geography and types of species.  They then created a statistical model to look first at whether some populations were in extreme decline and realized that those few species might be skewing the data. When they separated out the species in extreme declines, the overall picture changed to something they describe “as clustered rather than catastrophic.”

Declining Populations

What accounts for why some species are in such bad shape?  In a word, humans. The species that are doing the worst are the ones that are most vulnerable to human-induced environmental changes. For example, they found that half of the clusters of extreme decline were marine mammals in the Arctic. Birds and fish showed the biggest falls overall, and after that reptiles and amphibians. Mammals overall showed less extreme declines than other types of species. Another trend they found was that larger species fared worse than smaller species, which supports notions of trophic downgrading, meaning the loss of apex predators is causing smaller species to increase in a way that throws off the entire ecosystem. 

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