Articles The Global Decline of Reptiles,Dé jà Vu Amphibians J. WHITFIELD GIBBONS,DAVID E. SCOTT,T R AVIS J. RYA N ,KURT A. B U H L M A N N ,T R ACEY D. TUBERV I L L E ,BRIAN S. METTS,J UDITH L. GREENE, TONY MILLS,YALE LEIDEN, SEAN POPPY,AND CHRISTOPHER T. WINNE s a group [reptiles] are neit h er ‘good ’n or ‘bad , ’ but “ ia re interes ting and unu sua l , a lt h o u gh of mi nor A i m porta n ce . If th ey should all disappe ar , it wo ul d REP TI L E SPE CI E S AR E DE CL I N IN G ON A not make mu ch difference one way or the other ”( Zim and Smith 1953,p. 9) . Fortu n a tely,this op i n i on from the Golden GLO BA L SC A L E. SI XS I G N I F IC A N T TH R E ATS Gu ide Series does not persist tod ay;most people have com e TOR E P T I L EPO P ULA T I O N SAR E H A BI T AT to recogn i ze the va lue ofboth reptiles and amphi bians as an in tegral part ofn a tu ral eco sys tems and as heralds of LO SS A N DD E G RADA TI O N , I N T RO D U C E D environ m ental qu a l ity (Gibbons and Stangel 1999). In recent ye ars ,as overa ll environ m ental aw a reness among the IN VA S I V E SPE C I E S , EN VI RO N M E N TA L p u blic has increa s ed, con cerns have come to include intere st in the eco logical state ofreptile and amphi bian spec i e s PO L LUT I O N , DI S E A SE , UN S U S TA I NA B L E th em selves and oft heir habit a ts . Inc re a s ed awa reness may US E , A N D GLO BA L CL I M AT E C H A N G E stem from bet ter edu ca ti on abo ut threats to biod ivers ity in genera l , and to reptiles and amph ibians in parti c ul a r, a nd po s s ibly even from an innate attracti on to these taxa (Kell ert and Wil s on 1993). probl em ,as it has come to be known,has garnered sig- From the perspective ofmany nonscientists, the two nificant attention not only among scientists but also in the vertebrate classes comprising reptiles and amphibians, popular media and in political circles. collectively referred to as the herpetofauna, are inter- changeable.For example,the Boy Scout merit badge pam- The reptile problem phlet for herpetology was called simply Reptile Study from Despite the fact that reptiles and amphibians are often 1926 to 1993 (Conant 1972, Gibbons 1993), and major considered collectively,reptile declines deserve spotlight- zoos (e.g., National Zoo in Washington, DC; Zoo Atlanta; ing and elucidating in their own right. The differences and San Diego Zoo) use only the name “reptile”to refer to between the two groups are substantial. Modern amphib- the facility that houses both amphibians and reptiles. ians and reptiles are products ofindependent lineages that Thus, public attitudes about the need for conservation of have been separate for the past 300 million years (Pough et reptiles are probably linked to concern about amphibian al. 1998). Many ofthe differences between the groups are declines and deformities (Alford and Richards 1999,John- obvious and considerable.For example,the integument of son et al. 1999, Sessions et al. 1999), which have been the reptiles is covered with scales, whereas amphibians have a subject ofnumerous,well-documented scientific studies. highly permeable,glandular skin,a feature often touted as Because amphibians are distributed worldwide, but her- enhancing the environmental sensitivity ofamphibians to petologists who document amphibian declines are not,it is difficult to accurately assess what portion ofamphibian J. Whitfield Gibbons (e-mail: [email protected]) is a professor of populations are experiencing significant declines or have ec o l o gy at Savannah River Ecology Laboratory (SREL), Un iv ers ity of already disappeared. Furthermore,the means ofdeter- G e o r g i a ,A i ke n ,SC 29802. David E. Scott,Tr avis J. Rya n ,Tr a cey D. mining a species’conservation status is a rigorous and Tu be rv i l l e ,Brian S. Metts,Judith L. Greene,To ny Mills,Yale Leiden, time-intensive process, and therefore counts of“ officially” Sean Po p py,and Christopher T. Winne are researchers at SREL. recognized endangered and threatened species are likely to Kur t A. Buhlmann is coordinator for amphibian and chelonian con- grossly underestimate the actual number ofimperiled s e rvation at Conservation Intern a t i o n a l ,Center for Applied s pecies (Ta ble 1). The worl dwi de amph i bian decl i n e Bi o d i v e rsity Science, Wa s h in g t o n ,DC 20037. August 2000 / Vol. 50 No. 8 BioScience653 Articles Table 1. Con serva tion status ofreptiles and amphibi a n s ,a cco rding to the US Fish and Wi l dlife Service (FWS ) , Conven tion on Intern a tional Trade in En da n gered Species (CITES), and The Wo rld Con serva tion Union (IUCN). Ap p r ox i ma t e number of F WS b CI T ES c IU C N d Tax on s p e c i es a E nd a n ge r e d Th r ea t e n e dAppendix IAppendix II Appendix III E x t i nc t En da n g e r ed Vul n er ab l e A mp hi b ia n s 46 80 1 7 9 13 6 8 0 5 4 9 75 Frogs and toads4 1 00 9 5 1 1 6 6 0 5 3 8 5 0 S al a m an de rs 41 5 8 4 2 2 0 0 1 1 2 5 C ae c i l i an s 16 5 0 0 0 0 0 0 0 0 Re p ti l e s 7 15 0 70 1 8 70 38 3 1 9 2 0 1 00 15 3 Turt l es 26 0 33 4 2 5 4 9 6 6 3 8 5 8 C ro c o d i l i an s 22 1 5 3 1 6 8 0 0 7 3 Tua t a r a 2 2 0 2 0 0 0 0 1 L i z a r ds 5 06 6 14 8 1 6 2 38 0 1 1 30 66 S na ke s 1 8 00 6 3 1 1 8 8 1 3 3 2 5 2 5 aThe approxi m a te nu m ber of s pecies for each taxon is from Po u gh et al.( 19 9 8) . The num bers in the table refl ect worldwi de esti m ates of s pecies on ly ( excluding su bs pecies and pop ul a ti ons) listed by each orga n iz a ti on under sel ected cons ervati on ran k i n gs . bData from FWS (2000). cAppendix I species are threa ten ed with ex tin ction and are ,or may be ,a f fected by trade; Appendix II species are not current ly thre aten ed but are likely to become so unless trade is re stri cted ;Appendix III species are listed to prevent or re stri ct exp l oi t a ti on .Data from CITES (2000). d“Ex ti n ct” refers to com p l ete taxonomic ex tin cti on ,ra t h er than the IUCN category “ex ti n ct in wild ” ; “end a n gered ”i n clu des those species listed by IUCN as “cri tic a lly en d a n gered ” ;“ vu l n era ble” in d i c a tes that species are likely to become ex ti n ct if c urrent trends conti nue .Data from IUCN–W orld Cons erva- ti on Un ion (2000). toxic chemicals in both terrestrial and aquatic situations (Pseudechis porphyriacus ),a large frog-eating snake, due to (Vitt et al. 1990). Additionally,reptile eggs possess a cal- food shortages during extended drought conditions. Only careous shell,whereas amphibian eggs are enclosed by the smaller snakes survived, suggesting that large snakes simple gelatinous membranes, making the eggs more sus- may be relatively more susceptible to declines caused by ceptible to uptake ofenvironmental contaminants (but see food shortages.Gibbons (1990) reported a natural decline Pechmann and Wilbur 1994). The differences between for an isolated population ofslider turtles ( Trachemys amphibians and reptiles are not limited to morphology scripta) on a coastal island. The turtle population had no and reproductive biology;they also include ecological and juvenile recruitment, presumably because ofconstant pre- behavioral traits. Most amphibians rarely travel more than dation on smaller individuals by alligators ( Alligator mis- a few hundred meters over the course oftheir lives (Seml- sissippiensis ) that had become established on the island; itsch and Ryan 1998); many reptiles may move several only large adult turtles survived.