‘Bi­o­log­i­cal an­ni­hi­la­tion’ un­der­way, sci­en­tists warn

Pop­u­la­tion growth, in­creas­ing con­sump­tion putting count­less species at risk

The Hamilton Spectator - - FOCUS - TATIANA SCHLOSSBERG

From the com­mon barn swal­low to the ex­otic gi­raffe, thou­sands of an­i­mal species are in pre­cip­i­tous de­cline, a sign that an ir­re­versible era of mass ex­tinc­tion is un­der­way, new re­search finds.

The study, pub­lished this week in the Pro­ceed­ings of the Na­tional Academy of Sciences, calls the cur­rent de­cline in an­i­mal pop­u­la­tions a “global epidemic” and part of the “on­go­ing sixth mass ex­tinc­tion” caused in large mea­sure by hu­man de­struc­tion of an­i­mal habi­tats. The pre­vi­ous five ex­tinc­tions were caused by nat­u­ral phe­nom­ena.

Ger­ardo Ce­bal­los, a re­searcher at the Univer­si­dad Na­cional Autónoma de Méx­ico in Mex­ico City, ac­knowl­edged that the study is writ­ten in un­usu­ally alarm­ing tones for an aca­demic re­search paper. “It wouldn’t be eth­i­cal right now not to speak in this strong lan­guage to call at­ten­tion to the sever­ity of the prob­lem,” he said.

Ce­bal­los em­pha­sized that he and his co-au­thors, Paul R. Ehrlich and Rodolfo Dirzo, both pro­fes­sors at Stan­ford Univer­sity, are not alarmists, but are us­ing sci­en­tific data to back up their as­ser­tions that sig­nif­i­cant pop­u­la­tion de­cline and pos­si­ble mass ex­tinc­tion of species all over the world may be im­mi­nent, and that both have been un­der­es­ti­mated by many other sci­en­tists.

The study’s au­thors looked at re­duc­tions in a species’ range — a re­sult of fac­tors like habi­tat degra­da­tion, pol­lu­tion and cli­mate change, among oth­ers — and ex­trap­o­lated from that how many pop­u­la­tions have been lost or are in de­cline, a method that they said is used by the In­ter­na­tional Union for Con­ser­va­tion of Na­ture.

They found that about 30 per cent of all land ver­te­brates — mam­mals, birds, rep­tiles and am­phib­ians — are ex­pe­ri­enc­ing de­clines and lo­cal pop­u­la­tion losses. In most parts of the world, mam­mal pop­u­la­tions are los­ing 70 per cent of their mem­bers be­cause of habi­tat loss.

In par­tic­u­lar, they cite chee­tahs, which have de­clined to around 7,000 mem­bers; Bor­neo and Su­ma­tran orang­utans, of which fewer than 5,000 re­main; pop­u­la­tions of African lions, which have de­clined by 43 per cent since 1993; pan­golins, which have been “dec­i­mated”; and gi­raffes, whose four species now num­ber un­der 100,000 mem­bers.

The study de­fines pop­u­la­tions as the num­ber of in­di­vid­u­als in a given species in a 10,000-square-kilo­me­tre unit of habi­tat, known as a quadrat.

Jonathan Losos, a bi­ol­ogy pro­fes­sor at Har­vard, said that he was not aware of other pa­pers that have used this method, but that it is “a rea­son­able first pass” at es­ti­mat­ing the ex­tent of species de­cline and pop­u­la­tion loss.

Losos also noted that giv­ing pre­cise es­ti­mates of wildlife pop­u­la­tions is dif­fi­cult, in part be­cause sci­en­tists do not al­ways agree on what de­fines a pop­u­la­tion, which makes the ques­tion in­her­ently sub­jec­tive. De­spite those is­sues, Losos said, “I think it’s a very im­por­tant and trou­bling paper that doc­u­ments that the prob­lems we have with bio­di­ver­sity are much

African lion pop­u­la­tions have de­clined by 43 per cent since 1993. The barn swal­low pop­u­la­tion is in pre­cip­i­tous de­cline.

greater than com­monly thought.”

The au­thors of the paper sug­gest that pre­vi­ous es­ti­mates of global ex­tinc­tion rates have been too low, in part be­cause sci­en­tists have been too fo­cused on com­plete ex­tinc­tion of a species. Two ver­te­brate species are es­ti­mated to go ex­tinct ev­ery year, which the au­thors wrote “does not gen­er­ate enough pub­lic con­cern,” and lends the im­pres­sion that many species are not se­verely threat­ened, or that mass ex­tinc­tion is a dis­tant catas­tro­phe.

Con­ser­va­tively, sci­en­tists es­ti­mate that 200 species have gone ex­tinct in the past 100 years; the “nor­mal” ex­tinc­tion rate over the past 2 mil­lion years has been that two species go ex­tinct ev­ery 100 years be­cause of evo­lu­tion­ary and other fac­tors.

Rather than ex­tinc­tions, the paper looks at how pop­u­la­tions are do­ing: the dis­ap­pear­ance of en­tire pop­u­la­tions, and the de­crease of the num­ber of in­di­vid­u­als within a pop­u­la­tion. Over­all, they found this phe­nom­e­non is oc­cur­ring glob­ally, but that trop­i­cal re­gions, which have the great­est bio­di­ver­sity, are ex­pe­ri­enc­ing the great­est loss in num­bers, and that tem­per­ate re­gions are see­ing higher pro­por­tions of pop­u­la­tion loss.

Ehrlich, who rose to promi­nence in the 1960s af­ter he wrote “The Pop­u­la­tion Bomb,” a book that pre­dicted the im­mi­nent col­lapse of hu­man­ity be­cause of over­pop­u­la­tion, said that he sees a sim­i­lar phe­nom­e­non in the an­i­mal world as a re­sult of hu­man ac­tiv­ity.

“There is only one over­all so­lu­tion, and that is to re­duce the scale of the hu­man en­ter­prise,” he said. “Pop­u­la­tion growth and in­creas­ing con­sump­tion among the rich is driv­ing it.”

He and Ce­bal­los said that habi­tat de­struc­tion — de­for­esta­tion for agri­cul­ture, for ex­am­ple — and pol­lu­tion were the pri­mary cul­prits, but that cli­mate change ex­ac­er­bates both prob­lems. Ac­cel­er­at­ing de­for­esta­tion and ris­ing car­bon pol­lu­tion are likely to make cli­mate change worse, which could have dis­as­trous con­se­quences for the abil­ity of many species to sur­vive on earth.

Ce­bal­los struck a slightly more hope­ful tone, adding that some species have been able to re­bound when some of these pres­sures are taken away.

Ehrlich, how­ever, con­tin­ued to sound the alarm. “We’re tox­i­fy­ing the en­tire planet,” he said.

When asked about the clear ad­vo­cacy po­si­tion the paper has taken, a rar­ity in sci­en­tific lit­er­a­ture, he said, “Sci­en­tists don’t give up their re­spon­si­bil­ity as cit­i­zens to say what they think about the data that they’re gath­er­ing.”


An orang­utan in Kal­i­man­tan, In­done­sia. A study de­scribes the threat­ened mass ex­tinc­tion of thou­sands of an­i­mal species around the globe.



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