AboutZoos, Since 2008


Species extinc­tion rates have been over­es­ti­mated, but .…

pub­lished 05 June 2011 | mod­i­fied 21 April 2012

In a recently pub­lished arti­cle in the jour­nal Nature, sci­en­tists report that the most widely used meth­ods for cal­cu­lat­ing species extinc­tion rates are “fun­da­men­tally flawed” and over­es­ti­mate extinc­tion rates by as much as 160 per­cent. Nev­er­the­less, the global species extinc­tion cri­sis caused by habi­tat loss is real and a grow­ing threat.

This warn­ing by sci­en­tists who just stated that extinc­tion rates are over­es­ti­mated must not be dis­re­garded. Hope­fully, politi­cians and the pub­lic in gen­eral will take notice of the warn­ing of these crit­i­cal sci­en­tists. Their warn­ing is much more impor­tant than their mes­sage that when bet­ter meth­ods will be applied the extinc­tion rates will not be over­es­ti­mated any­more. When no steps will be taken to pre­serve habi­tats, and thereby pre­serve ani­mals and plants, they will be lost and gone forever.

Habi­tat loss is widely regarded as the main dri­ving force for species extinc­tion. There­fore con­ser­va­tion efforts are directed at the pre­ven­tion of this habi­tat loss, which is para­mount. Though there is agree­ment within the research and con­ser­va­tion com­mu­nity about the impor­tance of extinc­tion, the rates of this phe­nom­e­non are still highly uncer­tain. As no proven direct meth­ods or reli­able data exist for ver­i­fy­ing extinc­tions. The indi­rect method sci­en­tists and con­ser­va­tion­ists have used until now is called a “species-​area rela­tion­ship”. This method starts with the num­ber of species found in a given area and then esti­mates how the num­ber of species grows as the area expands. Using that infor­ma­tion, sci­en­tists and con­ser­va­tion­ists did back­ward extrap­o­la­tions to esti­mate how many species will remain when the amount of land decreases due to habi­tat loss. Dr. Hubbell, one of the authors, says: “In the Nature paper, we show that this sur­ro­gate mea­sure is fun­da­men­tally flawed. The species-​area curve has been around for more than a cen­tury, but you can’t just turn it around to cal­cu­late how many species should be left when the area is reduced; the area you need to sam­ple to first locate a species is always less than the area you have to sam­ple to elim­i­nate the last mem­ber of the species”.

The warn­ing of the sci­en­tists regard­ing the effect of habi­tat loss has been artic­u­lated on UCLA’s web­site where Hubbell says: “There have been five mass extinc­tions in the his­tory of the Earth, and we could be enter­ing the sixth mass extinc­tion. Humans are already using 40 per­cent of all the “plant bio­mass” pro­duced by pho­to­syn­the­sis on the planet, a dis­turb­ing sta­tis­tic because most life on Earth depends on plants. Some three-​quarters of all species thought to reside on Earth live in rain forests, and they are being cut down at the sub­stan­tial rate of about half a per­cent per year”.

(Sources: Nature, 19.05.2011; UCLA news­room, 18.05.2011)

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