AboutZoos, Since 2008


Earth’s 6th mass extinc­tion event under way, a pre­lude to global extinc­tion, sci­en­tists warn

pub­lished 19 July 2017 | mod­i­fied 19 July 2017

In the first such global eval­u­a­tion, Stan­ford biol­o­gists found more than 30 per­cent of all ver­te­brates have declin­ing pop­u­la­tions. They call for curbs on the basic dri­vers of these losses.

Christmas Island Pipistrelle Lindy LumsdenNo bells tolled when the last Cata­rina pup­fish on Earth died. News­pa­pers didn’t carry the story when the Christ­mas Island pip­istrelle van­ished for­ever.

Two ver­te­brate species go extinct every year on aver­age, but few peo­ple notice, per­haps because the rate seems rel­a­tively slow — not a clear and present threat to the nat­ural sys­tems we depend on. This view over­looks trends of extreme decline in ani­mal pop­u­la­tions, which tell a more dire story with cas­cad­ing con­se­quences, accord­ing to a new study that pro­vides the first global eval­u­a­tion of these pop­u­la­tion trends.

This is the case of a bio­log­i­cal anni­hi­la­tion occur­ring glob­ally, even if the species these pop­u­la­tions belong to are still present some­where on Earth,” said co-​author Rodolfo Dirzo, a pro­fes­sor of biology.

Map­ping loss
A 2015 study co-​authored by Paul Ehrlich, pro­fes­sor emer­i­tus of biol­ogy, and col­leagues showed that Earth has entered an era of mass extinc­tion unpar­al­leled since the dinosaurs died out 66 mil­lion years ago. The spec­tre of extinc­tion hangs over about 41 per­cent of all amphib­ian species and 26 per­cent of all mam­mals, accord­ing to the Inter­na­tional Union for Con­ser­va­tion of Nature (IUCN), which main­tains a list of threat­ened and extinct species — the IUCN Red List of Threat­ened Species. This global dis­as­ter scene has the fin­ger­prints of habi­tat loss, over­ex­ploita­tion, inva­sive organ­isms, pol­lu­tion, tox­i­fi­ca­tion and cli­mate change.

Stanford’s Paul Ehrlich warns that Earth has entered an era of mass extinc­tion:

The new analy­sis, pub­lished online on 10 July in Pro­ceed­ings of the National Acad­emy of Sci­ences, looks beyond species extinc­tions to pro­vide a clear pic­ture of dwin­dling pop­u­la­tions and ranges. The researchers mapped the ranges of 27,600 species of birds, amphib­ians, mam­mals and rep­tiles — a sam­ple rep­re­sent­ing nearly half of known ter­res­trial ver­te­brate species — and analysed pop­u­la­tion losses in a sam­ple of 177 well-​studied mam­mal species between 1990 and 2015.

Using range reduc­tion as a proxy for pop­u­la­tion loss, the study finds more than 30 per­cent of ver­te­brate species are declin­ing in pop­u­la­tion size and range. Of the 177 mam­mals for which the researchers had detailed data, all have lost 30 per­cent or more of their geo­graphic ranges and more than 40 per­cent have lost more than 80 per­cent of their ranges. Trop­i­cal regions have had the great­est num­ber of decreas­ing species while tem­per­ate regions have seen sim­i­lar or higher pro­por­tions of decreas­ing species. Par­tic­u­larly hard hit have been the mam­mals of south and south­east Asia, where all the large-​bodied species of mam­mals analysed have lost more than 80 per­cent of their geo­graphic ranges.
Sixth mass extinctionThe per­cent­age of species of land mam­mals from five major continents/​subcontinents and the entire globe under­go­ing dif­fer­ent degrees (in per­cent­age) of decline in the period ∼19002015. Con­sid­er­ing the sam­pled species glob­ally, 56% of them have lost more than 60% of their range, a pat­tern that is gen­er­ally con­sis­tent in Africa, Asia, Aus­tralia, and Europe, whereas in South Amer­ica and North Amer­ica, 3540% of the species have expe­ri­enced range con­trac­tions of only 20% or less.
Credit: Ger­ardo Cebal­los, Paul R. Ehrlich, and Rodolfo Dirzo. Bio­log­i­cal anni­hi­la­tion via the ongo­ing sixth mass extinc­tion sig­naled by ver­te­brate pop­u­la­tion losses and declines. PNAS 2017.

The study’s maps sug­gest that as much as 50 per­cent of the num­ber of ani­mal indi­vid­u­als that once shared Earth have dis­ap­peared, as have bil­lions of ani­mal pop­u­la­tions. This amounts to “a mas­sive ero­sion of the great­est bio­log­i­cal diver­sity in the his­tory of Earth,” the authors write.

The mas­sive loss of pop­u­la­tions and species reflects our lack of empa­thy to all the wild species that have been our com­pan­ions since our ori­gins. It is a pre­lude to the dis­ap­pear­ance of many more species and the decline of nat­ural sys­tems that make civ­i­liza­tion possible.

Ger­ardo Cebal­los, lead author, National Autonomous Uni­ver­sity of Mexico

Cas­cad­ing effects
Why does the loss of pop­u­la­tions and bio­log­i­cal diver­sity mat­ter? Aside from being what the sci­en­tists call a pre­lude to species extinc­tion, the losses rob us of cru­cial ecosys­tem ser­vices such as hon­ey­bees’ crop pol­li­na­tion, pest con­trol and wet­lands’ water purifi­ca­tion. We also lose intri­cate eco­log­i­cal net­works involv­ing ani­mals, plants and microor­gan­isms — lead­ing to less resilient ecosys­tems and pools of genetic infor­ma­tion that may prove vital to species’ sur­vival in a rapidly chang­ing global environment.

Sadly, our descen­dants will also have to do with­out the aes­thetic plea­sures and sources of imag­i­na­tion pro­vided by our only known liv­ing coun­ter­parts in the uni­verse,” said Ehrlich.

In the mean­time, the over­all scope of pop­u­la­tion losses makes clear the world can­not wait to address bio­di­ver­sity dam­age, accord­ing to the authors. They call for curbs on the basic dri­vers of extinc­tion — human over­pop­u­la­tion and over­con­sump­tion — and chal­lenge soci­ety to move away from “the fic­tion that per­pet­ual growth can occur on a finite planet.”

Video report by the Guardian:

(Source: Stan­ford Uni­ver­sity press release, 10.07.2017; The Guardian, 11.07.2017)

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Tiger range countries map

Tiger map” (CC BY 2.5) by Sander­son et al., 2006.

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