Independ Study WildlfFish Sci
Independ Study WildlfFish Sci WFS 493
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JOURNAL or NATURAL l llS39l ORY 1998 32 140371409 Caecilian viviparity and amniote origins M WILKINSONf and R A NUSSBAUM lSt39lmol of Biological Srimrutt39 Univz39rxily rql39Brixlul ErisOI BS8 I UG UK and Dcpurmt39m flow1g The Nttlm39ul His0111 Museum Lottim 5 W7 580 UK iDivisiun of Hmpemlngy Muscum nZnaogy Ultit39elzt39itt of Michigan Amt Arbor tlliz ltigun 48I09I7 USA Accepted KY Marc1 199th recent evaluation of alternative hypothe for the origin ot the amniotic egg by mapping a single reproductivemode character onto a phylogeny ot39tetrapods concluded tltat the alternative hypotheses were equally parsimonious However this interpretation is dependent upon a mis aken codng ol the caecilian amph39 bians as showing extended embryo retention Although some caecilians are vivi parous phylogenetic analyses indicate that oviparity is ancestral for the group With the coding ol caecilians corrected the most parsimonious inference is that the ane tral nmniotes did not practice extended embryo retention A review 0139 the available data indicates that the widespread View that a majority ot caccilians are vivipztrous is mistaken Oviparity is the dominant reproductive mode in caecilians as it is in other living amphibians KtYVORlSi Evolution phylogeny parsimony Amniota Gymnophiona repro ductive modes Introduction Explanations ol major transitions in evolution are alien necessarin highly specu lative because the transitions happened in the distant past and because the evidence from the record is too incomplete to allow some scenarios to be ruled out Not surprisingly then many workers are turning to phylogenetic hypotheses and a ociated parsimonious interpretations of character evolution to provide frame works tor the additional testing ol evolutionary scenarios A recent but problematic example is provided by Lattrin and Reiszs 1997 discussion ol the evolution of amniotes and the origins 01 their key innovation the amniotic egg 5 Antniote origins Laurin and Re 2 t 997 presented a novel hypothct ol39 tetrapod phylogenetic relationships gure I and used this as a Framework to explore two alternative scenarios for the origin of the amniotc egg C2 roll 1970 199 speculated that alnniotcs evolved from terrestrial anamniotcs that laid their eggs on land as do some quot 39 39 39 tr39tm ili m frogs 39 The characteristic cxtracmbt yv onic membranes of amniotcs evolved as adaptations ol terrestrial eggs In contrast Lombardi H994 and Laurin and Reisz t 997 speculated that the amniotic incur HUD2 13 9X SIZMU 39 le Tailor k innitis I Hi 1404 M Wilkinson and R A Nussbaum branes evolved in association with embryo retention and provided a pathway tor t39oetal inaternal interaction taurin and Reisz I997 evaluated these alternative scenarios by mapping a binary character extended embryo retention present or absent onto their phylogeny The optimimlion of their character is ambiguous such that both the presence and 11 39ence ol extended embryo retention in ancestral amniotes are equally parsimonious gure I They concluded p 34 the scenario that the evolution ol the amniotic condition involved the ititennediate stage ot anamniotie eggs being laid on land is not more parsimonious than the alternative suggested here that extratembi39yonie membranes evolved to Facilitate extensive embryo retention However the conclusion is dependent on the character states that they attributed to terminal laxu In particular it is dependent upon their erroneous coding ol eaecilians as showing extended egg retention Citeeilians display a number of repro ductive modes including extended egg retention in the form ofquot viviparity Many phylogenetic analyses based on both morphology and molecules Nassbaum 1979 Duellnian and Trueb 986 Hillis 199 l39ledges 39I a 1991 Wilkinson and Nussbiium 9 6 Wilkinson 1996 l997 strongly suggest that vi iparity is a derive condition that has probably arisen a number of times within caeeilians figure 2 These analyses conlirm the longheld VlC39 cg DLllllL I942 that the primitive reproductive mode in caeciliatis is oviparity with eggs hatching into freeliving larvae that undergo metamorphosis tie the characteristic amphibian biphasie life history with no extended embryo retention lli caecilians are recoded so as to correctly re ect this ancestral condition the optimization ol39extended embryo retention on Laurin and Reisz39s phylogeny changes and it becomes more pa imonious to conclude that the ancestral amniotcs did not practice extended embryo retention ligure 3 Judged solely on the basis ol the lit m n g 8 S N a 2 m a a g a E 2 E g quot3 g 2 5 8 I a 3 D c g 3 G Q 0 O u E I D gt m Uquot h gt I D lt D lt 0 I f O lt I u D in I I g E g Cl ancestral ammote Extended embryo ratentlon polymorphic E equivocal l iti l Tetrapotl phylogeny with the binary character extended er retention present or absent mapped onto the tree by MacClade lMtidtlisiitt and Muddison HUI l39tcr Laurin and Reis7 977 The condition of ancestral ainniotes with respect to this character is ambiguous Caeeilian viviparity and amniote origins 14115 I Rhinatrematidae IZIUraeotyphlidae EScolecomorphidae lTyphlonectidae I Ulchthyophiidae ECaeciliidae Reproductive Mode viviparous polymorphic E Equwocal Fin 2 Caeeilian altvhwenv with the hittar char ter Vivi arit extentletl cue retention 1 c 1 P Y e or oviparity mapped onto the tree by M lth Matldison and Maddison 1992 Caecilians are inferred to have been ovipttrous ttncestrally This phylogeny is based on that of Wilkinson and Nussbaum t 1996 and Wilkinson 1997 and tillers from other workers only in the position of the Liraeotyphlidae Alternative phylogenies cg Duelltmtti and Trueb 1986 Hillis 199 place Uraeotyphlidae as the sister group 0139 the scolecon tot39phid eaeeiliid typhlonectid elade and do not alleet the inferred ancestral reproductive mode F to the phylogeny the extended embryo retention hypothesis for the origin 01 the amniote egg is not as well supported as Carroll39s hypothesis This result provides some support For Carroll s scenario although its signi cance depends upon the reliability of the p11y10genythe plausibility oflcss parsimonious schemes ofcharacter evolution and the import ot39whulever other evidence can be brought to bear on the alternative scenarios Thus we echo Laurin and Reisz s I997 34 view that this aspect of the origin 01 amnioles needs further study39 Caecilian viviparity Laurin and Reisz 1997 did not explain their coding of eaeei 39ans with respect to extended embryo retention but their misinterpretation of caeeilian reproduction presumably stems from the widespread but mistakctL View that Viviparity is the dominant reproductive mode in eaecilians combined with the assumption that common equals primitive The latter commonality principle is Far from perfect and the phylogenetic considerations that suggest that viviparity is not primitive for caecilians figure 2 illustrate why Furthermore the many assertions that the major ity 01 caecilian species are or probably are viviparous cg Wake 1977 1986 1992 1993 Dttellman and Trueb 1986 Pough u ale 1989 Stebbins and Cohen 1995 are not supported by the available evidence The most direct inferences of caecilian reproductive modes come from observa 1406 M Wilkinson and R A Nussbaum U 9 U a a E w I DTestudines I Latimeria l39flSquamata D Dipnoi EIAves ancestral E equivocal FIG 3 Tetrapod phylogeny with the biliary character extended eg retention present or absent mapped onto the tree by MaeClade Maddison and Maddison 1992 alter correction of the coding ol caecilians Apoda from present to absent The parsimonious interpretation is unambiguous and indicates the absence of extended embryo retention in the ancestral amniote ions of parturitiont clutches ol eggs larvae and oviductal foetuses Unfortunately because eaecilian amphibians are mostly secretive burrowing tropical forms such observations are unavailable for the great majority ol the approximately 160 caecilian species More indirect inferences that make use ol several lines ol evidence are possible Chief among these are Oviduetal egg size Large eggs are associated with oviparous species small eggs with viviparity Wake 1977 Nussbaum 1985 Morphological features of young specimens that may betray a larval or l octal existence No eaeeilian species are known that have both viviparity and a free living larval stage Premetaniorphic larvae or juveniles with larval features such as lateral line organs labial l39olds and spiracles thus provide evidence For the absence ol vlviparity Wilkinson 1992 Foetal caecilians possess a characteristic 39tquotoetal dentition that is thought to be used in feeding from the hypertrophied maternal oviduct lining Parker 956 and foetal39 teeth in young specimens have been taken as evidence of reeent parturition and vivipar ity in the genus Cactiill However the young of some eaeeilians such as Sip101ml Minntins Mikan and S uuensi Boettger that are known to be oviparous Goeldi 1899 Gans l961 C Jared pers comm also have the apparently inisnanied l39oetal39 dentition M Wilkinson pcrs obs eg S urinululns Museu Nacionul Rio de Janeiro Nos 1863348637 S muensis Muscu de Zoologia Universidadc de Sao Paulo 7 No 36724 Furthermore at least some Cavriliu are de nitely oviparous having laid eggs in captivity R A Nussbaum pers obs These observations indicate that viviparity cannot be reliably inferred from observations of foetal teeth in young specimens to Caecilinn viviparity and zlmniote origins I407 3 Extrapolation from other ini crcnces bused on the assumption that species of the same genus or family or other closely related group have the same reproductive mode ici parsimony lnl erenccs ol the taxonomic distribution of reproductive moch in cuecilians are summarised in table 1 On the basis of the most direct observations combined with Table 1 Distribution ot reproductive modes across L itcciiim gcncru Oovipari1yz V viviparity 3 uncertain Letters in parentheses indicutc more indiract inferences Taxa Number ol species Reproductive mode Rhinatrcmatiduc Epiu immpt 8 O lemlrenm I 70 I lchthyophiid uudm m 5 O IrIlhya t 32 O Uraeotyphlidae Unlmepilus 4 O Scolecmnorphidue raluplmlrmm 2 O SCHPHIIHIII IJIIUN 3 V Typhloncctidue A In owloam 1 II V C Izllmm i39pcmn 7 V erlm39am39ilia l V Pummulypim l V J 73911II7TI39 3 Czteciliiduc Boulmgel39nlu 5 O Brnxilulypilm l I39 Cactiit 32 O Dermanin 3 V Gt39gwteuphn 3 O Gmlrypclm 3 V inmdismtiu 4 O Zrmnupix 2 V Heme139 2 7 I 1771 gimpi is I O Iim rmlimn l O Indurypzlus l Lulkc ImIJWIIux l 1 M icrut39ueciiu 5 7 M imr39iplmnupl39 2 397 39 39 9 39ItOd Parviz39uz39ciiu 2 7 PrayIlia l O Sl39llit39ll71 ltlII 2 V S ipmnopx 5 O Srlmr39zmciliu 1 O inference based on close phylogenetic relationship to Epicriwzops Nussbaum l977 l inl crence based on size oi39ov d Nussbaum 1985 inl erence based on close phylogenetic relationship to other typhloncctids Wilkinson and Nussbaum 1997 dinl erencc based on close phylogenetic relationship to uuiia Nussbaum and Wilkinson 1989 Wilkinson 1997 1408 M Wilkinson and R A Nussbaunt the assumption that all species 0139 a genus have the same reproductive mode 13 genera and 102 species are oviparoos whereas only eight genera and 24 species are viviparous and for 12 genera and 28 species the reproductive mode is unknown Incorporating hypothesised reproductive modes based upon additional indirect infer ences redue39s the extent of ignorance to seven genera and 14 species produces a slight i11Ct39Ck e in the extent of viviparity to ten genera and 26 species and a slightly more substantial increase in oviparity to lo genera and 114 species The above estimat indicate that the predominant eaeei an reproductive mode is oviparity with viviparity occurring in only 24 to 30 of genera and 15 to 17 of species for which inference of reproductive mode is possible Oviparity occurs in 39 to 48 of genera and a clear majority 66 741 of species If our estimates and inferences are correct then in terms of numbers of species oviparity would remain the predominant eaecilian reproductive mode even in the unlikely event of all species for which reproductive mode cannot be inferred proving to be viviparous Discussion The view that viviparity is the predominant reproduetire mode in eaeeilians appears to have originated with Wake l977 83 who stated that 50 11 of the species having a known reproductive mode are livehearersquot and I suspect that further data will demonstrate that the majority ofeaecilian species are livebearers However in Wake39s t 1977 review which focused on the available reproductive data for indi vidual eaecilian species and did not employ indirect inferences based on extrapola tions to genera or other presumed phylogenetic groups the number of species listed as oviparous 24 actually slightly exceeds the number known to be viviparous 17 This persistent error has in uenced under39 anding of quotteeilian evolution and the relation of caecilians to other Amphibia For example caceilian viviparity has been identitied as one of the key adaptations in the evolution of the lineage that sets the group apart from other Amphibiu in which viviparity is rare Wake 1986 More surprising is its potential signi cance as seen here for interpretation of the origins of the Aniniota Acknowledgements This work was supported in part by NERC grants ESTA 832 and GIN02881 We are grateful to C Jared for sharing his lield observations on SipHumps mmumm and Dave Gowcr John Measey Peter Miller and Joe Thorley for disc 39ons and comments on the manuscript MW thanks Miguel l ret39aut Rodrigues and Paulo Vanzolini Museu de Zoologia Universidade lc Silo Paulo and Ulisees Caramaschi and Jose Pombal Jr Muscu Naeionul Rio dc Janeirnl for facilitating his studies of the eaceilian collections in their care References CAI thJIJ R L 1970 Quantitative aspects of the ampliihianreptilian transition Funmt I I39illlt li 3 165 171 Cannot l R 1 I991 The origin of reptiles 1I1 ll P Schultze and L Trueh eds l39igim 39 Iivr grail1r nf rerrnpmls ranI39urr39rxr and i39nnxmtrm Ithaca Comstnck Publishng oeiates pp 3317 335 67 7 DUNN E IL 1942 The American caeeilians Bulletin u Ilw Museum u wnpunuire liloHui llurrm39zl l 43 540 Global Amphibian Declines A Problem in Applied Ecology Ross A Alford Stephen J Richards Annual Review of Ecology and Systematics Vol 30 1999 pp 133165 Stable URL http1inksjstororgsicisici0066416228199929303C1333AGADAPI3E20CO3B2B Annual Review of Ecology and Systematics is currently published by Annual Reviews Your use of the J STOR archive indicates your acceptance of J STOR39s Terms and Conditions of Use available at httpwwwjstororgaboutterms html J STOR39s Terms and Conditions of Use provides in part that unless you have obtained prior permission you may not download an entire issue of a journal or multiple copies of articles and you may use content in the J STOR archive only for your personal noncommercial use Please contact the publisher regarding any further use of this work Publisher contact information may be obtained at httpwwwjstororgjoumalsannrevs html Each copy of any part of a J STOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission J STOR is an independent notfor profit organization dedicated to and preserving a digital archive of scholarly journals For more information regarding J STOR please contact supportjstororg httpwwwjstororg Tue Apr 3 100635 2007 Annu Rev Ecol Syst 1999 30l3365 Copyright 1999 by Annual Reviews All rights reserved GLOBAL AMPHIBIAN DECLINEs A PROBLEM IN APPLIED ECOLOGY Ross A Alford and Stephen J Richards School of Tropical Biology and Cooperative Research Centre for Tropical Rainforest Ecology and Management James Cook University Townsville Queensland 4811 Australia email rossalfordjcueduan Key Words conservation frog salamander null hypothesis metapopulation I Abstract Declines and losses of amphibian populations are a global problem with complex local causes These may include ultraviolet radiation predation habi tat modi cation environmental acidity and toxicants diseases Changes in climate or weather patterns and interactions among these factors Understanding the extent of the problem and its nature requires an understanding of how local factors affect the dynamics of local populations Hypotheses about population behavior must be tested against appropriate null hypotheses We generated null hypotheses for the be havior of amphibian populations using a model and we used them to test hypotheses about the behavior of 85 time series taken from the literature Our results suggest that most amphibian populations should decrease more often than they increase due to highly variable recruitment and less variable adult mortality During the period covered by our data 1951 1997 more amphibian populations decreased than our model predicted However there was no indication that the proportion of populations decreasing changed over time In addition our review of the literature suggests that many if not most amphibians exist in metapopulations Understanding the dynamics of amphibian populations will require an integration of studies on and within local populations and at the metapopulation level INTRODUCTION The current wave of interest in amphibian population biology and in the possibility that there is a global pattern of decline and loss began in 1989 at the First World Congress of Herpetology 10 By 1993 more than 500 populations of frogs and salamanders on ve continents were listed as declining or of conservation concern 189 There is now a consensus that alarming declines of amphibians have oc curred 30 51 125 147 192 Because most amphibians are exposed to terrestrial and aquatic habitats at different stages of their life cycles and because they have highly permeable skins they may be more sensitive to environmental toxins or to changes in patterns of temperature or rainfall than are other terrestrial vertebrate 00664162991 12001330800 133 134 ALFORD RICHARDS TABLE 1 Techniques used in 46 studies1 to quantify populations of frogs salamanders Many studies used more than one technique or studied both taxa so the total number of techniques used does not equal the number of studies cited Technique Habitat2 Frogs Salamanders Egg mass counts B 4 1 Counts of individuals B 12 1 Drift fencepit trap counts B 7 8 Mark recapture estimates3 B 7 2 Calling male counts B 3 NA Dipnet samples for larvae B 2 2 Counts of individuals N 1 6 Mark recapture estimates N 0 1 Aquatic traps N 0 1 1Sources used in compiling table 15 19 20 21 41 49 53 54 63 64 73 83 84 86 88 90 91 92 96 102 107 111 113 117 131 136 137 142 157 158 159 160161165169170171174177178179180181194196202 2B Breeding N Nonbreeding 3Includes in descending order of frequency used J ollySeber Petersen ManlyParr Schnabel and Zippin techniques groups 29190 The bestdocumented declines have occurred in Europe and North America are usually associated with habitat modi cation 87 116 and are often attributed to interactions among causal factors 114 125 147 The fac tors associated with population declines in relatively undisturbed habitats such as montane tropical rainforests have been more dif cult to elucidate 131 163 Although they have been the subject of many experimental and monitoring studies the autecology of amphibians in nature is poorly understood 87 The majority of studies of ecology and population biology of amphibians Table 1 have been conducted on aggregations at reproductive sites Relatively little is known of their movements or activities away from breeding sites or of rates of exchange between populations Many authors have suggested that there is a need for longterm studies di rected toward a combination of understanding ecological theory and increasing knowledge of the autecology of amphibians 17 39 79 80 190 Simple long term programs that monitor the uctuations of single populations and associated environmental factors and then apply standard population models are unlikely to be useful for understanding the dynamics of amphibian populations as they have not worked for that purpose when applied to other terrestrial vertebrates 164 It appears likely that understanding the problem of amphibian declines will require much more information on the ecology of the metapopulations in which many species live 87 GLOBAL AMPHIBIAN DECLINES 135 Our goals in this review are to summarize and synthesize the literature on potential causes of amphibian declines and to use the literature on amphibian population dynamics to develop a null hypothesis for the behavior of amphib ian populations We then use our null hypothesis and data from the literature to determine whether the incidence of declines has recently increased Finally we place the dynamics of amphibian populations and their declines in the context of metapopulation dynamics POTENTIAL CAUSES OF AMPHIBIAN DECLINES Ultraviolet Radiation Depletion of stratospheric ozone and resultant seasonal increases in ultraviolet B UVB radiation at the Earth s surface 119 have stimulated interest in the possible relationship between resistance of amphibian embryos to UV B damage and population declines Signi cant variation among species in levels of pho tolyase a photoreactivating DNA repair enzyme that repairs UV B damage is correlated with exposure of natural egg deposition sites to sunlight 25 98 In a survey of 10 Oregon amphibian species photolyase activity and hence ability to repair UV damage was lowest in declining species and highest in nondeclining species 25 Field experiments demonstrated that embryos of Hyla regilla a non declining species with high photolyase activity had signi cantly higher hatching success than did two declining species Rana cascadae and Bufo boreas with low photolyase levels 25 A number of other studies have demonstrated that ambient 6 2428 132 or enhanced 144 UV B radiation reduces survival or hatching success of amphibian embryos Synergistic interactions between UV B and other environmental stresses such as pathogens 120 and low pH 133 may also signi cantly increase embry onic mortality Rana pipiens embryos that are unaffected when exposed to UV B and low pH separately have signi cantly reduced survival when exposed to these factors simultaneously 133 Other studies have produced more equivocal results Rana aurora is a declining species with high levels of photolyase 98 and experimental hatching success is unaffected by exposure to UV B 26 The declining frog Liz oria aurea from eastern Australia has a lower photolyase activity than two sympatric nondeclining species L dentaz a and L peroni but there is no signi cant difference among the three species in hatching success under UV B exposure 187 In many aquatic habitats UV B radiation is largely absorbed in the rst few centimeters of the water column 138 so increased UV B may only affect species breeding in habitats with a narrow range of chemical and physical parameters Ecologically relevant levels of UV B had no effect on embryos of several Canadian amphibians and experimental protocols used to test UV impacts have been questioned 85 130 Most studies that have examined the relationship between UV B and population declines have focused their attention on species that breed in shallow clear water 136 ALFORD I RICHARDS where exposure to UV B is expected to be greatest 6 25 28 132 Exposure to intense UV B in shallow highaltitude ponds may exclude amphibians from these habitats 138 Even when UV B causes higher embryonic mortality in declining species the ecological signi cance of this at the population level is dif cult to assess More needs to be understood about the basic natural history of amphibian species that might be at risk For example information is needed on variation in oviposition site characteristics depth vegetation within local populations Experiments at natural oviposition sites using embryos of Ambystoma macrodactylum were con ducted in shallow water although this species lays eggs in a variety of microhabitats 28 Loss of a large proportion of nearsurface clutches to UV B damage may have negligible impacts on populations if even a small number of deeper clutches survive as the survivors are released from densitydependent effects 1 Even fewer data are available to assess the indirect effects of increasing UV B on amphibian populations Potential indirect effects include changes in water chemistry and food supplies and shifts in competitive and predatorprey relation ships with other UV B affected species 143 Exposure to increased UV B may reduce survival rates of adult amphibians through damage to eyes 77 increased frequency of cancers or tumors 143 and immunosuppression 143 Predation Biotic interactions among amphibians and between amphibians and other organ isms can play a signi cant role in determining their distribution and population dynamics 1 Larval amphibians are extremely vulnerable to vertebrate and in vertebrate predators 1 and the diversity of aquatic amphibian assemblages is frequently reduced in habitats containing predatory sh 1 100 Larval amphibians that coexist with aquatic predators have evolved a range of antipredator mechanisms 4 48 118 However widespread introductions of predatory sh have increasingly exposed native amphibians to predators with which they have not previously interacted Inappropriate responses to novel preda tors may increase mortality of native amphibians 82 121 leading to signi cant effects on populations Colonization of normally sh free water bodies by predatory sh can result in rapid extinction of amphibian assemblages 76 The allotopic distributions of native frogs and introduced shes in many highelevation gt 2500 m asl Sierra Nevada lakes indicate that introduced predatory shes have caused the extinc tion of local frog populations there 31 Sixty percent of lakes that frogs could formerly occupy now contain introduced shes and no frogs Fish introductions have had a particularly severe impact on Rana muscosa which breeds in the deep lakes inhabited by shes 31 A similar pattern of allotopic distributions has been recorded for larval newts Taricha torosa and an introduced sh Gambusia a nis and cray sh Procambarus clarki both predators of newt eggs or larvae in Californian mountain streams 82 GLOBAL AMPHIBIAN DECLINES 137 Introduced predators may also have more subtle effects Some Rana muscosa populations persisting in shfree environments have become isolated from other populations by surrounding aquatic habitats containing introduced shes This may eventually lead to regional extinction by preventing migration among local populations 35 North American bullfrogs Rana catesbeiana that have become established outside their natural range have been implicated in declines of native frogs 76 102 127 but see 97 Adult bullfrogs consume native frogs and reach densities at which they are likely to have a severe impact on local amphibian populations 166 Experimental studies have shown that Rana aurora larvae exposed to adult or larval bullfrogs have increased larval periods smaller mass and when exposed to both lower survival 122 Humans have devastated frog populations in several countries for the frog leg trade Before 1995 about two hundred million frogs were exported annually from Asia By 1990 India was still illegally exporting approximately seventy million frogs each year resulting in serious population declines 145 Habitat Modi cation Habitat modi cation is the best documented cause of amphibian population de clines Habitat loss certainly reduces amphibian abundance and diversity in the areas directly affected 99 101 Removal or modi cation of vegetation during forestry operations has a rapid and severe impact on some amphibian populations 8 Clearcutting of mature forests in the southern Appalachians has reduced sala mander populations by almost 9 or more than a quarter of a billion salamanders below the numbers that could be sustained in unlogged forests 149 Logging ex poses terrestrial amphibians to drastically altered microclimatic regimes 9 soil compaction and desiccation and reduction in habitat complexity 197 It ex poses aquatic amphibians to stream environments with increased siltation 5 2 and reduced woody debris 43 Although populations may recover as regenerating forests mature recovery to predisturbance levels can take many years 9 and may not occur at all if mixed forests are replaced with monocultures 108 Draining wetlands directly affects frog populations by removing breeding sites 116 and by fragmenting populations 74168 which increases the regional probability of extinction e g 5 3 Modi cation of terrestrial and aquatic habitats for urban development can reduce or eliminate amphibian populations Popula tions of some amphibians in urban Florida declined after degradation of upland dry season refuges and modi cation of wetlands used for breeding 62 Protection of aquatic breeding sites may be of little value if adjacent terrestrial habitats used by amphibians for feeding and shelter are destroyed 167 More subtle alterations to habitat structure can have severe impacts on amphib ian populations Bufo calamita populations in Britain declined over a 40 year period due to shifts in land use practices that altered vegetation characteristics 13 Changing vegetation structure and an associated increase in shading were 138 ALFORD II RICHARDS detrimental to B calamita and provided conditions under which the common toad Bufo bufo became a successful competitor Although habitat alterations can reduce amphibian populations in some cases even severe habitat modi cations can have little effect The response of a savanna woodland frog assemblage at Weipa Queensland Australia to strip mining appears in Figure 1 200 The structure and oristics of the plant assemblage at 60 revegetated sites vary widely none strongly resemble the original native woodland Percent of sites Limnooynastes omatus Bufo ma nus Liton39a caeruea Liton39a bicolor Cyclorana novaeholandiae Litoria rubella Sphenophome gracilipes Limnodynastes convexiuscuus Liton39a gracienta Liton39a rothi 1 Cn39nia remote Uperoleiea mimua Uton39a infrafrenata w thon39a nasuta Figure 1 Pro les of percent of sites of ve habitat types at Weipa Queensland Australia at which frogs of 14 species occurred Species sorted in order of frequency of occurrence in native woodland Dots and solid lines indicate native woodland habitat 13 sites Diamonds and dashed lines indicate sites revegetated following strip mining Density of diamonds re ects age of revegetation from least to most dense this is age 5 7 years 7 years lt age 5 105 years 105 years lt age 5 16 years age gt16 years There were 15 revegetation sites in each age group in the survey GLOBAL AMPHIBIAN DECLINES 139 The distance from revegetation sites to native woodland varies from a few meters to over 1 km Despite this within 7 years the majority of frog species occur at revegetation sites at frequencies very similar to the frequencies at which they are found at sites in native woodland This indicates that the frogs in this assemblage are insensitive to radical alterations in the soil characteristics ora and structure of their terrestrial habitat and they can recolonize rapidly following disturbances that have eliminated them over a relatively wide area It is possible that other amphibian species assemblages behave similarly Acidity and Toxicants The acidity of aquatic habitats has major impacts on amphibian distribution re production and egg and larval growth and mortality 78 79 Sensitivity to low pH varies among 79 and within 150 species and is in uenced by complex chemical interactions among pH and other factors particularly aluminum concen tration 71 110 151 Mortality occurs in both the embryonic and larval stages via several mechanisms including incomplete absorption of the yolk plug arrested development and deformation of larvae 11 79 109 Sublethal effects of acidi cation include delayed 109 or early 36 hatching reduced larval body size 36 disturbed swimming behavior 5 and slower growth rates resulting from reduced response to and capture of prey 155 Indirect sublethal effects include changes to tadpole food sources through impacts on algal communities 188 and shifting predator prey relationships resulting from differential mortality of predatory sh and invertebrates in acidi ed habitats 104 The population level effects of acidity are less well understood It is possi ble that the effects of low pH in combination with other abiotic factors lead to decreased recruitment into adult populations 12 Acidic breeding sites of ten contain less diverse amphibian assemblages at lower densities than do less acidic sites 205 Long term acidi cation of ponds in Britain has excluded Bufo calamita from many sites 16 Reduced pH and increased metal concentrations in an Appalachian stream eliminated virtually all salamander larvae causing se vere long term declines in populations of Desmognathus quadramaculatus and Eurycea wilderae 124 Low soil pH also in uences the distribution abundance and diversity of terrestrial amphibians 204 205 Despite the well documented effects of low pH on amphibians there are few data to implicate acidi cation in recent unexplained catastrophic population de clines Acid deposition was proposed as a factor in the decline of tiger salamanders Ambysz oma tigrinum in the Rocky Mountains 96 but subsequent eld studies demonstrated that mortality due to pond drying was equally likely to be the cause of this decline 201 Acid deposition is unlikely to be involved in population de clines of frogs and salamanders at high altitudes in the Sierra Nevada Mountains 33 34 36 and Rocky Mountains 54 55 188 201 There may be no rigorously documented cases where acidi cation of natural habitat has led to the extinction of an amphibian population 71 However studies of acid tolerance have been biased toward species that are likely to have evolved tolerance to low pH 195 140 ALFORD E RICHARDS Similarly although there is an extensive literature on the toxic effects on larval amphibians of metals and chemicals used in insecticides and herbicides 154 in suf cient data exist to determine their long term impacts on amphibian population dynamics 22 Environmental toxicants act directly to kill animals or indirectly by impairing reproduction reducing growth rates disrupting normal development and reproduction endocrine disruption or increasing susceptibility to disease by immunosuppression or inhibition of immune system development 22 46 Diseases Little is known about the diseases of wild amphibians Many disease agents are present in healthy animals and disease occurs when immune systems are compro mised 56 57 Declines in populations of Bufo boreas boreas between 1974 and 1982 were associated with Aeromonas hydrophila infection but Carey 47 sug gested that environmental factors caused sublethal stress in these populations directly or indirectly suppressing their immune systems A pathogenic fungus largely responsible for egg mortality in one population of Bufo boreas in Oregon may have been more virulent to embryos under environmental stress 27 Epidemics can cause mass mortality of amphibians 123 In 1981 Aeromonas hydrophila killed all larval Rana sylvatica in a Rhode Island pond and three years later few adult frogs were breeding at this site 141 The same bacterium was implicated in a well documented decline to local extinction of a population of Rana muscosa in California 32 A chytridomycete fungus found on moribund anurans in Australia and Panama during mass mortality is fatal to healthy frogs under experimental conditions 18 This fungus was proposed as the proximate cause of declines in these two regions 18 but this hypothesis is untested at present Viruses have been isolated from dead and dying frogs during mass mortal ity events 59 60 and may be the primary cause of mortality in animals where other infections such as bacteria have been identi ed 57 Laurance et al 129 argued that the pattern of population declines among Australian rainforest frogs was indicative of a wave of epidemic disease caused by an unidenti ed water borne virus This interpretation was challenged 3106 on statistical grounds and because numerous other explanations for the observed patterns were equally parsimonious The involvement of a virus in these declines has now been largely discounted but the possible involvement of a disease has not The pattern of pop ulation declines in Central America has also led to the suggestion that a wave of epidemic disease might be responsible 131 Climate Weather Immediately prior to the disappearance of golden toads Bufo periglenes the rain forests of Monteverde Costa Rica had the lowest twelve month rainfall in 20 years Toads were forced to shift their habitat use and the dry conditions may have interacted with an unidenti ed factor such as disease or a pulse of contaminants GLOBAL AMPHIBIAN DECLINES 141 in cloud water to eliminate toad populations 152 Unusual weather conditions were dismissed as a cause of declines of Australian rainforest frogs 128 This result relies on seasonal rainfall totals calculated for xed groups of months while in northern Australia the date of onset of the wet season is highly variable occur ring between October and February 140 The analysis is therefore likely to have missed the extremes and underestimated the variances of rainfall and a reexam ination of the data seems warranted Severe short term climatic events such as violent storms can alter the dynamics of amphibian populations Hurricane Hugo caused extensive damage to the forests of Puerto Rico in 1989 In the short term populations of the terrestrial frog Eleutherodactylus richmondi decreased by 83 but increased availability of ground cover due to disturbance led to a six fold in crease in the densities of E coqui followed by a long period of gradual population decrease 202 203 Alterations in local weather conditions caused by global climate change will in uence the ecology of amphibians in a number of ways The onset of spawning in Rana temporaria in Finland between 1846 and 1986 shifted earlier by 213 days following shifts in air and water temperature and dates of snow cover loss 182 At some sites in Britain there has been a statistically signi cant trend toward earlier rst sighting and spawning of Bufo calamita Rana esculenta and R temporaria between 1978 and 1994 correlated with changing patterns of spring temperatures 14 Amphibians in Canada are affected by decreases in summer precipitation and increased temperatures and winter rainfall 105 143 In the neotropics increased temperatures extended dry seasons and increasing inter year rainfall variability may affect litter species by reducing prey populations and altering amphibian distributions on increasingly dry soil 67 Shifting rainfall patterns will affect the reproductive phenologies of pond breeding species Ponds will ll later and persist for shorter periods leading to increased competition and predation as amphibians are concentrated at increasingly limited aquatic sites 67 Frogs exposed to these stresses may also become more vulnerable to parasites and disease 67 Interactions Among Environmental Factors Most studies invoke multiple causes or interactions among factors Increased UV B exposure may alter species interactions or vulnerability to pathogens or changes in pH Predation may eliminate local populations and have larger scale effects by altering rates of migration between populations Outbreaks of disease may only occur when other stresses reduce immune function Pesticides pollu tants and environmental acidity may interact to produce unforeseen effects All local effects may interact with global climate change Proving the existence of these complex effects in natural populations will require well planned programs of observation and experimentation To plan such studies and to determine how stresses affect population behavior requires an understanding of the nature of the populations being studied and the limitations of study techniques It also requires 142 ALFORD I RICHARDS the development of null hypotheses regarding how amphibian populations behave in the absence of external pressures DEFINING AND STUDYING AMPHIBIAN POPULATIONS Monitoring and Censusing Techniques We have summarized the techniques used in 46 long term population studies of frogs and salamanders in Table 1 All but one of the studies of frogs were carried out at breeding sites while about half of the studies of salamanders included at least some data collected on densities of animals in nonbreeding habitat The most commonly used technique is direct counts where animals are located by intensive searching localization of calls or by drift fences with pitfall traps Many studies that reported direct counts also reported the results of markrecapture estimates Frequently however the standard errors of markrecapture estimates are very large so that counts are regarded as being better estimates The high standard errors typically obtained in markrecapture estimates of animals at breeding sites probably re ect the fact that the degree of attraction of breeding sites varies widely over time as does the activity of individual animals near them Problems with Studying Breeding Aggregations as Populations Most estimates of frog populations are expressed in units such as total numbers of frogs attending a pond numbers of frogs per m2 of pond area and maximum numbers of frogs at a pond on a single night during the breeding season 70 The frog groups for which data are available on densities in nonreproductive habitat tend to be species that do not aggregate at breeding sites 70 115 203 A few studies have examined aquatic breeding species in nonreproductive habitats 156 206 The use of breeding aggregations in population studies can cause problems in data interpretation A simple illustration of why censusing amphibians at breeding sites can cause problems in the interpretation of population dynamics appears in Figure 2 The number of frogs per unit of nonreproductive habitat the entire rectangle remains constant at 50 In Figure 2a neither of the temporary pools in the habitat contains water If censuses are carried out by visiting pool 1 a census at the time of Figure 2a would detect only 7 10 frogs in the habitat A census carried out after pool 1 lled Figure 219 would detect 43 frogs while one carried out after both pools lled Figure 2c would detect only 23 frogs at pool 1 Similar variations in measured density could occur over time even if the pools remain lled because of changes in the reproductive behavior of frogs Changes in habitat availability and in the attractiveness of bodies of water are both likely to affect the numbers of amphibians detected 191 complicating the use of data of this type as an indi cation of the size or density of the population occupying the surrounding habitat Because behavior and site attributes vary seasonally and temporally with weather GLOBAL AMPHIBIAN DECLINES 143 Figure 2 An illustration of the dif culties for data interpretation created by sampling animals in breeding aggregations An area of habitat contains a xed number of animals and two potential breeding sites Surveys are carried out at site 1 In 62 animals are not attracted to breeding sites so a census at site 1 would encounter only 9 10 individuals In 9 animals are attracted to site 1 and a census would nd 43 animals In 6 animals are attracted to both sites and a census at site 1 would encounter 22 animals All of these situations may occur within a few days in many habitats making counts at breeding sites highly variable and internal rhythms of the animals the best hope for obtaining accurate estimates using censuses at breeding sites is to perform censuses frequently Effects of Sampling Intensity on Population Size Estimates We used data collected by one of us SJ Richards unpublished data on the number of adult males of the streambreeding hylid Litoria genimaculata to investigate the effects of sampling intensity on the accuracy of count data taken at a breeding aggregation A 60 m transect along a rainforest stream site was Visited an average of 19 times each year over seven years All frogs on the transect were counted marked and released We used a resampling technique to explore how less intense sampling might have affected the results We set the probability that a Visit would occur to 075 05 and 025 and resampled the data set 5000 times using each of these probabilities It is apparent Figure 3 that decreasing the intensity of sampling below about 075 times the number of Visits actually made would greatly decrease the accuracy of the annual means obtained At intensities of 05 025 144 ALFORD I RICHARDS au k ualnrxmi 35 75 sampling 50 sampling m 25 sampling 1m tperyear 1989 1990 1991 1992 1993 1994 1995 16 25 21 1O 17 22 23 Year Number of visits Figure 3 Results of resampling analysis on numbers of adult male Litoria genimac ulata present on a 60m transect on Birthday Creek Mt Spec Queensland Australia Points indicate the mean number of individuals present taken over all visits in each year The lines connecting the points are for illustration only The dashed lines at increasing distances from the mean are the upper and lower 95 con dence limits for the location of the mean for each year at the given sampling intensity as determined from 5000 resamplin gs of the data Upper and lower solid lines are the 95 con dence limits for numbers obtained if the site was visited once annually they are the minimum and maximum numbers encountered each year Mean number of Litoria genimaculata present GLOBAL AMPHIBIAN DECLINES 145 or one visit per year the observed pattern of change through time would probably have differed from the pattern that appears in the full data set and the coef cient of variation of the annual mean would have increased substantially Problems created by the changing attractiveness of breeding sites can also occur when animals are censused in nonreproductive habitat because the attractiveness of patches changes A population of Rana arvalis in a 2000m2 sampling area increased more than tenfold over the period 1984 1988 89 this might have been due to a decrease in the local availability of water causing animals to concentrate where it was available 89 Densities of the neotropical litter frogs Bufo typhonius and Colostethus nubicola in nonreproductive habitat varied more than tenfold over the course of a one year study 183 This variation was probably caused by differences in the activity level and catchability of frogs rather than by changes in population size 183 Once a reasonable set of population estimates at a site is available the next step in an analysis of the behavior of the population is to examine how it changes over time It is unrealistic to expect perfect stability from any natural population even if the population is truly constant sampling error will introduce some variation Given that we expect populations to uctuate we should try to determine how they will behave over time in the absence of directional pressures toward expansion or decline A Null Hypothesis for the Behavior of Amphibian Populations over Time There has been substantial debate in recent years 23 146 148 169 regarding how normal amphibian populations should change through time but little theoretical work on this question The problem has been de ned clearly Fluctuating popula tions of amphibians will be either increasing or decreasing at any time 146 148 There is a very large opportunity for bias if populations are declared to be declin ing on the basis of short time series indicating that numbers are decreasing Amphibian Populations F actuate It is almost universally agreed that most lo cal populations of amphibians are likely to uctuate considerably in size This occurs because recruitment is highly variable 7 15 20 44 65 81 185 186 194 Survival rates of terrestrial stages often appear to be relatively constant with some degree of uctuation 7 44 73 185 186 The survival rates of eggs hatchlings and larvae often vary over several orders of magnitude 1 20 199 Pechmann amp Wilbur 148 provided a useful review of approaches that have been used to examine population behavior Examining Changes of Numbers with Time One approach that has been used to examine trends within populations of amphibians is simple correlations of numbers with time Fifteen totwenty year time series for six species of salamanders in the Appalachian mountains of the United States showed no evidence for consistent 146 ALFORD I RICHARDS trends in numbers over time 91 A lack of signi cant correlations of numbers with years over a longterm study may indicate that variation among years repre sents uctuations in numbers rather than declines 146 169 Signi cant negative correlations between population size and time have been interpreted as indicating that populations are in decline 115 117 Of 16 studies that monitored amphibian populations for four or more years ve reported that populations were declining one that six populations had become extinct seven that populations were uctu ating and three that they were stable 30 Most of the evaluations of population change were based on correlations of population size with time and some state ments that populations were not in decline were based on failure to nd a signi cant correlation Failure to nd a signi cant correlation does not necessarily imply that none exists 162 it can also result from a lack of statistical power In eight studies of amphibian populations that reported no trend in population size over time the power of a product moment correlation was insuf cient to allow acceptance of the null hypothesis 162 Reed amp Blaustein 162 suggested that studies should not conclude that populations are not in decline unless that conclusion can be sup ported statistically Unfortunately the power analysis they used relying on simple Pearson correlations is not statistically valid as the adjacent annual values in time series on a single population are not independent random samples We develop an alternative approach below A Simple Model of Population Behavior In order to suggest how more appro priate tests might be carried out we explored how time series data on amphibian populations should be analyzed and interpreted and what the normal patterns in such data might be We constructed a simple verbal model of frog population dynamics and compared its predictions with the behavior of 57 time series of frog abundances and 28 salamander time series all studies cited in Table 1 details are available on the World Wide Web in the Supplemental Materials section of the main Annual Reviews site wwwAnnualReviewsorg Finally we compared the behavior of those 85 time series with that of a simulated population The simple verbal model is Assumptions 1 amphibian populations often persist for many generations neither decreasing to extinction nor exploding to in nity 2 survival rates of terrestrial stages may vary but that variation is typically over less than a single order of magnitude 3 survival rates of aquatic stages often vary over several orders of magnitude Deductions A Assumption 1 implies that recruitment must on average be suf cient for replacement to occur B Assumptions 1 and 2 together imply that most variation in the size of terrestrial populations must be due to uctuations in recruitment from the aquatic stages C Assumptions 1 2 and 3 together imply that when aquatic survival is high populations must rapidly increase but that aquatic survival must frequently be below replacement level so that the increases do not tend to lead to sustained explosions Deductions A C taken together GLOBAL AMPHIBIAN DECLINES 147 suggest that populations should decrease more often than they increase because increases can be very rapid and must be counterbalanced by slower decreases This model suggests that populations of species with highly variable recruitment from the aquatic to the terrestrial stage might be expected to decrease during more than 50 of time intervals This is a potentially important point in the context of the problem of amphibian declines If populations naturally decrease in numbers more often than they increase relatively short term population studies may often nd that the population or populations studied appear to be in decline Comparing the Predictions of the Model with Data To examine this problem in more detail we extracted data from a database of information on time series of population sizes of frogs and salamanders collated from the literature and available from the United States Geological Survey USGS 72 Most of the populations studied were not regarded as being in decline We modi ed the database from its raw form in several ways The database includes a number of time series collected using different techniques on the same species at the same sites and times We included only one time series of data on any species for any site and set of dates We did not use data on larvae or juveniles in our analysis because they re ect reproductive input modi ed by highly variable aquatic mortality rates and so are least likely to re ect the dynamics of adult populations When data were available for both male and female adults we combined them When count data and other estimates such as mark recapture values were available we included the count data if they had been collected in a manner that was likely to be comparable among years otherwise we used the estimated numbers When only data on numbers of egg masses were available we included them in our analyses as they should be highly correlated with numbers of adult females We included only time series taken over four or more years We also included data from Cohen 50 that were not present in the USGS database A summary of the original sources of the data we used appears in Table l and details of the data for each time series appear on the World Wide Web in the Supplemental Materials section of the main Annual Reviews site wwwAnnualReviewsorg We classi ed each yearly population estimate as either the initial number in a series an increase a decrease or no change Three families of frogs Bufonidae Hylidae and Ranidae and two families of salamanders Ambystomatidae and Plethodontidae contained suf cient numbers of time series We used nonpara metric statistics Table 2 to determine whether the percentage of the time in which populations decreased from one year to the next varied among families In both orders families differed in the percentage of the time that populations declined between years In the Caudata populations of species in the family Ambystomati dae which are pool breeding species with relatively large clutch sizes decreased between years an average of 592 of the time Species in the Plethodontidae primarily terrestrial egg layers and stream breeders with smaller average clutch 148 ALFORD I RICHARDS TABLE 2 Means standard deviations and numbers of time series analyzed for the percentage of yeartoyear changes in population size that are decreases for amphibians of ve families and tests for signi cant differences in the mean among families within orders Percent of population changes that are decreases Family Mean Standard Deviation N Salamanders Wilcoxon 2sample test Z 243 P 0015 Ambystomatidae 592 181 12 Plethodontidae 420 161 14 Frogs KruskalWallis test x2 882 2 df P 0012 Bufonidae 555 198 19 Hylidae 473 67 15 Ranidae 606 130 23 sizes see references in Table I declined between years only 42 of the time In the Anura species in the families Ranidae and Bufonidae decreased in more than 50 of intervals while species in the family Hylidae decreased in slightly less than 50 of intervals Table 2 The ranids and bufonids included in the database generally produce larger clutches of eggs and often have highly variable offspring survival while hylids produce smaller clutches and may have less variable rates of offspring survival references in Table l The results of this analysis suggest strongly that the expected behavior of pop ulations over time varies among families of frogs and salamanders and that the adult populations of species that have more variable survival of premetamorphic offspring tend to decrease between years more often than they increase This result has implications for the ability to draw conclusions about population trends from simple time series of numbers over years A species in the family Plethodontidae in which the mean population behavior is to decrease between 40 of years has a probability of four successive decreases of only 0031 and nding four successive decreases between years in a censused population might be cause for alarm How ever a ranid species would need to decrease in numbers six times in succession before the probability of that sequence of decreases was less than 005 Our data set included populations from many times and places some of which might have been undergoing declines caused by external pressures This would bias the results of our analysis To erect a null hypothesis independent of the data from natural populations we examined the behavior of a simulated population with known characteristics A Numerical Model of Population Behavior For comparison with our verbal model and the results of our data analysis we used a simulation model based on a GLOBAL AMPHIBIAN DECLINES 149 long term study of the population dynamics of Bufo marinus in northern Australia 2 Our model incorporated simple density dependence in the adult stage and lognormal variation in recruitment success Mean recruitment rates were adjusted so that populations tended to uctuate about a mean size rather than explode or decline rapidly to extinction The population arbitrarily started with 100 adult female toads Year toyear survival of adult females was set at the lower of 50 or 50 total Each female produced 9000 eggs which survived to reach maturity as females in one year at variable rates equal to 000047 where a is a normally distributed random variable with mean 0 standard deviation 1 The number of adults was truncated to an integer following survival and recruitment in each year We ran the simulation 5000 times for 1000 years each time On average the population persisted for 423 years before extinction and contained 296 adult females while extant Within a run recruitment differed on average approximately 300 fold between the lowest and highest years while adult survival differed 15 fold as a consequence of density dependence While the population persisted it decreased in 5632 of intervals between years a result that is in very close agreement with the observation Table 2 that populations of bufonids declined between 555 of years This suggests that our initial verbal model was correct When population uctuations are driven by highly variable recruitment it is likely that population dynamics will be characterized by occasional outbreaks with longer intervening periods of decrease so that they are in decline more than 50 of the time This result is similar to the storage effect in open populations 45 193 It is clear that a population decreasing in more years than it increases is not nec essarily in decline However if there has recently been an increase in the general tendency of amphibian populations to decline there should be a correlation be tween the year in which a study ended and the frequency of decreases in that study We tested this hypothesis using the 85 time series in our database We correlated the nal year of each study with the percentage of intervals across which the studied population declined We analyzed the data for each family of frogs and salaman ders separately as combining them might have confounded real effects of time with the effects of changes in the proportions of studies that were carried out on each taxon We calculated Spearman rank correlations because these straighten nonlin ear relationships and decrease the effects of outliers and data that are not normally distributed We found no evidence for any signi cant correlation of proportion decreases with time in any family maximum rs 0327 minimum P 0234 an outcome supported by examination of the data Figure 4 which do not suggest any strong trend for either frogs or salamanders The proportion of years in which a population declines may be a weak indicator of trends and is potentially subject to dif culties in deciding how large a change in population size represents a real decrease rather than noise in the data Correlations between population size and time might be a better indicator of population status 30 148 150 ALFORD I RICHARDS O quot 393 I I 39 I I 1985 1990 1995 2000 Year frogs I 1 980 3 9 8 100 0 OD U C 9 80 0 ltgtltgt E El 0 j ltgt 3 ltgt ltgtltgt mo 839 60 ltgt ltgt ltgt on o ltgt o a u ltgtltgtltgt ltgtIZIltgtltgtltgt 30 IIID T5 3940 ltgt 0 0 0 DE E 8 0 3953 E E 5 20quot 9 5 8 o I I I I I I 39 I 39 I 1945 1955 1965 1975 1985 1995 Year salamanders Figure 4 Proportion of the intervals from one year to the next over which populations decreased during longterm studies 4 or more years of 85 local amphibian populations 28 of salamanders shown as squares 57 of frogs shown as diamonds The abscissa is the nal year of each study CORRELATIONS OF POPULATION SIZE WITH TIME If there is a general global phenomenon acting on all amphibians and increasing their tendency to decrease in numbers we would expect that recently completed studies would show more or stronger negative relationships between population size and time than would older ones For each of the 85 time series in our database we regressed log10N 1 on year of the series We used log10N 1 because this GLOBAL AMPHIBIAN DECLINES 151 stabilizes variances and because a population increasing or decreasing at a constant proportional rate will show a linear relationship of log10N 1 with time Years were adjusted within each time series so that the rst year was year zero to reduce possible in uences of rounding errors on the regressions We used the correlations and slopes of these regressions in further analyses to determine whether there was any evidence for an overall trend toward an increase in the incidence or intensity of negative relationships between population size and time In these analyses we examined the data for frogs and salamanders separately because trends might be present in one but not in the other We rst looked for correlations of either the slope or the correlation coef cient with the year in which each time series ended using Spearman rank correlations because of the unknown sampling properties of these two measures None of the correlations of the correlation coef cient or the slope with nal year were signi cant salamanders r 2 0021 P 0917 and rs 0024 P 2 0905 frogs rs 0175 P 2 0174 and rs 0161 P x 0232 respectively Although there was no trend in either order for changes over time in the relation ship of population size to year of study it is still possible that a general declining trend was present throughout the period To examine this possibility we plotted the correlations of population size with year and the slopes of the regressions of population size on year against nal year of the study Figure 5a and 519 Initial examination of these gures could be a source of alarm because there are many more negative than positive correlations and because most of the apparently sig ni cant correlations and slopes are negative Further analysis shows that both of these effects are probably artifacts of the population dynamics of amphibians and the fact that standard assessments of signi cance should not be applied to time series data In order to more rigorously assess the signi cance of these correlations and slopes we returned to the results of our population simulation On each of the 5000 iterations of the time series we calculated correlations and slopes for regres sions of log10N 1 on year for time series containing 4 through 9 11 12 14 15 16 23 and 28 years starting arbitrarily at year 20 of the simulated time series to allow the effects of initial conditions to disappear This resulted in at least 4904 coef cients for each combination of parameter and series length less than 5000 because a few populations went extinct before the nal year of each simulated series We sorted the vector of coef cients for each combination of parameter and series length into ascending order and we took the coef cients at 0025 from the bottom and top of the series as the upper and lower 95 con dence limits for the correlation and slope of regressions of an amphibian population on year These con dence limits appear in Figure 5 c and d with plots of the correlations and slopes obtained from the time series in our database Using the criterion that to be signi cant a parameter must fall outside these empirical 95 con dence limits only a single correlation and four slopes are signi cant well within the number that would be expected due to Type I error when 85 comparisons are made Although we must conclude that there is no evidence in the 85 time series we an alyzed to suggest that correlations or slopes of regressions of log10N 1 against 152 ALFORD I RICHARDS S 10 t 04 5 a 0 E9 g b D E 05 0 8 D 02 O I g 0 8 cg E g o O I 5 00quot 00 E g 0 OQJD 3 00 90 0E l o a o 3 8 0 9 o I g O5 g 008 0 J 5 02 o E 3 1O 2 E g 40 9 a i 39 39 5 04 I 39 I 39 I I 39 I I 39 I I I 39 I 1980 1985 1990 1995 2000 1980 1985 1990 1995 2000 Year frogs Year frogs I I 39 I I I I I 39 I I 39 I 39 I 39 I 1945 1955 1965 1975 1985 1995 1945 1955 1965 1975 1985 1995 Year saiamanders Year salamanders g gt 10 CM g 03 d39 75 08 ltgt 11 gt D g 05 DO C 02 quot OE o D I E 0439 so A 01 g o2 0 CB g c 00 80 00 V Eb 0 E9 3 u 3 02quot 0 Do 0 o 5 o1 quot6 04 O 8 16 0 g B 02 g 08 ltgt 5 03 5 4390quot g m 39I I I I l 39 I 39 I 39 I 39 39 39 0 1o 20 30 0 10 20 30 Years in time series Years in time series Figure 5 a Productmoment correlation of log10N 1 with year of study for 85 time series of four or more years of data on local populations of amphibians plotted against nal year of the study Data for salamanders shown as squares frogs as diamonds Correlations that would be signi cant at or 005 using standard parametric criteria are indicated by lled shapes 9 Slopes of regressions of log10N 1 on year of study other details the same as in a c The same correlation coef cients as in a plotted against number of years in the time series from which the correlation was derived Lines indicate upper and lower 95 con dence limits derived from correlations calculated on 5000 simulated time series of each length Only the single correlation outside these con dence limits should be considered signi cant indicated by the lled shape d The same slopes as in b plotted against number of years in the time series from which they were derived Lines indicate 95 con dence limits derived as in 6 Only four of the 85 slopes should be regarded as signi cant at the 005 level lled shapes GLOBAL AMPHIBIAN DECLINES 153 time have changed in recent years we might still be concerned over the apparent excess of negative relationships of population size with time Figure 5 a and b Fiftyseven of the 85 relationships of population size with time 67 are negative The proportion of negative correlations from our simulation increased with length of the time series from 548 negative with a series length of 4 years to 575 with a series length of 28 years We used these expected proportions weighted by the number of each of the real time series that were of each length to calculate the expected numbers of correlations that should have been greater and less than 0 376 and 474 respectively and compared these with the observed numbers 28 and 57 using a chisquared goodness of t test chisquared 442 P 2 0037 This signi cant result indicates that the amphibian populations we examined had a greater number of negative correlations with time than would be expected as compared with our simulated populations This could re ect a general tendency toward decline but it could also re ect the fact that our simulation model while it probably provides a more realistic null hypothesis than the simple assumption that effects in both directions should be equal does not perfectly re ect the pop ulation behavior of all amphibians Using a greater variety of models to generate null hypotheses more appropriate for each family genus or even species would obviously be preferable It would also be useful to examine the sensitivity of our conclusions to variations in model parameters and form The use of appropriate null hypotheses will allow more rigorous examination of the behavior of individual populations However many amphibians appear to live in local populations that interact strongly with other populations so that un derstanding the implications of local population dynamics for species persistence requires a knowledge of their metapopulation biology AMPHIBIAN METAPOPULATION BIOLOGY A metapopulation consists of a group of local populations inhabiting more or less discrete patches of habitat 94 A metapopulation differs from a collection of independent populations in that there is substantial migration between local populations so that no local population is likely to remain extinct for any length of time Migration rates may be high enough to affect rates of local population increase and decrease 95 139 A metapopulation differs from a single subdivided population by having suf ciently low rates of migration between local populations that they exhibit some degree of independence in their dynamics including the possibility of declining to extinction 93 Metapopulation Studies on Amphibians Although it has been suggested that amphibians are generally highly philopatric 3061 172 many species depart from this pattern One of the problems that plagues markrecapture studies of amphibian populations at single sites is the high 154 ALFORD l RICHARDS rates at which animals disappear from local populations 2 31 40 111 134 156 Substantial rates of dispersal among local populations have been documented in many species 2 21 37 38 42 58 66 81 112 161 173 198 Additional evi dence that many amphibians live in metapopulations comes from explicit metapop ulation studies 175 Breeding populations of the newt Notophthalmus viridescens act as cells in a regional metapopulation 83 The European pool frog Rana lessonae lives in spatially complex metapopulations the quality of potential breed ing sites and their degree of isolation from other sites determines their proba bility of occupancy and the probability of local extinction 176 Increases in the isolation of habitat patches due to natural succession or habitat destruction decrease the persistence of local populations 176 Surveys of Rana clamitans occupancy at 160 ponds in three distinct regions 103 demonstrated the ex istence of regional metapopulations Colonization rates varied from 0 to 025 ponds pond occupied year1 while local extinction rates were between 0 and 05 ponds pond occupied year1 Small populations were more prone to local extinction than were large ones and there was no overall trend in occupancy rates when all three metapopulations were considered 103 Ten other species examined at 97 ponds in the same regions 101 also exhibited metapopulation dynamics with rates of turnover from 007 to 030 species pond year1 Pool size and isolation both affected species richness in 77 pools in the southern Netherlands 126 and 332 habitats in Bavaria 68 Models of Amphibian Metapopulations and Their Implications Because amphibians often live in metapopulations declines and extinctions of local populations may be common events Detailed studies of local populations may give useful insights into the autecology of species but they are of limited use in evaluating the status of regional metapopulations One approach to exam ining the behavior of metapopulations is to examine simple probabilistic models for the frequency with which local populations might change in status 184 A probabilistic null model for population declines and disappearances was used to examine whether the declines and disappearances of frogs that occurred in the 1980s at Monteverde Costa Rica might be due to chance 153 Pounds et al 153 used longterm studies to estimate probabilities of disappearance They then compared the numbers of species disappearances at their study sites to the numbers of disappearances predicted by the cumulative binomial distribu tion and they found that far more species had disappeared than would have been predicted The probabilistic approach 153 seems to be a useful way to quantify the idea that when certain regions or taxa are considered species are disappearing at a rate too great to be coincidental Several studies have produced data that could be examined using this technique It seems likely that the disappearances of seven species from all sites at elevations above 400 m throughout the Australian Wet Tropics 135163 would be shown to be extremely improbable as would the GLOBAL AMPHIBIAN DECLINES 155 disappearances of three species and large declines in site occupancy of four others in the Yosemite area of California 69 the disappearance of Rana cascadae from the southern end of its range 75 and the disappearances of many species at Las Tablas Costa Rica 131 A more complex analytical model was used to predict the rates of extinction of local populations of the common toad Bufo bufo and the crested newt Triturus cristatus in Europe and to examine how those rates should respond to the size of the local habitat patch and its distance from a source of migrants 92 The persistence of populations of both species should increase with the carrying capacity of the local habitat and should decrease with increasing distance to a source of migrants Over a wide range of carrying capacities the critical distances are approximately 10 times as great 5 km for toads as they are for newts 500 m 92 This study suggested that both patch size and spatial distribution must be taken into account when managing amphibian metapopulations Information on patch occupancy from a geographically referenced database 168 indicates that small relatively isolated wetlands are important in the metapopulation dynamics of amphibians in South Carolina USA Loss of these habitats might lead to disproportionately large rates of extinction in regional metapopulations that depend upon them as stepping stones in colonization and as refuges from local extinctions 168 Delineating and monitoring the status of metapopulations requires extensive sampling but because metapopulation dynamics are concerned mostly with the presence or absence of species in local populations sampling of local populations does not need to be intense 87 Fully understanding the dynamics of amphibian metapopulations will require much more information on movements and dispersal among local populations than is presently available CONCLUSIONS It is clear that local populations of many amphibian species have declined in recent years and there are several welldocumented cases of declines at and above the level of regional metapopulations Although many environmental factors can adversely affect the growth survival and reproduction of amphibians few studies have convincingly demonstrated that these effects alter their population dynamics Studies linking factors that negatively affect amphibians in the laboratory or in arti cial eld trials with effects on population dynamics in more natural settings are urgently needed Local populations of amphibians tend to uctuate and our results show it is likely that many normally decrease more often than they increase It is therefore important to develop realistic null hypotheses for their behavior If we had not based our null hypothesis on a simulation of frog population dynamics we would have reached very different conclusions in our analysis of population behavior Additional data on an ecologically diverse range of species will allow the devel opment of more sophisticated and speci c null hypotheses for a greater range of 156 ALFORD l RICHARDS populations This is necessary to make rigorous tests of the responses of local populations to environmental factors possible Many amphibian species occur as metapopulations so the dynamics of local populations may be poor indicators of their status Declines and extinctions of metapopulations are likely to result from interactions between changes in the dy namics of local populations and habitat modi cation or loss 93 94 168 For many species understanding the factors affecting the status and dynamics of metapopulations should therefore be the ultimate goal of studies aiming to prevent or reverse declines Monitoring metapopulations requires different data collection techniques than monitoring isolated populations so the rst step in designing any monitoring program should be to determine whether the species of interest forms a metapopulation Studies integrating research within local populations with in vestigations at the metapopulation level are most likely to discover the causes of amphibian declines and provide a basis for the conservation of amphibian diversity ACKNOWLEDGMENTS The original data included in this review were collected with the support of funding from the Australian Research Council and the Cooperative Research Centre for Tropical Rainforest Ecology and Management We thank J Winter and the Com monwealth Aluminium Corporation for permission to include data from Reference 200 and S Droege for permission to use data extracted from the USGS amphibian count database 72 The manuscript was improved with the help of MJ Caley CN Johnson and L Schwarzkopf Visit the Annual Reviews home page at httpwwwAnnualReviews0rg LITERATURE CITED 1 Alford RA 1999 Ecology resource use competition and predation In Tadpoles The Biology of Anuran Larvae ed RW Mc Diarmid R Altig Chicago Univ Chicago Press In press Alford RA Cohen MP Crossland MR Heamden MN Schwarzkopf L 1995 Pop ulation biology of Bufo marinas in northern Australia In Wetland Research in the Wet Dry Tropics of Australia ed CM Finlayson pp 173 181 Canberra Commonwealth of Australia Alford RA Richards SJ 1997 Lack of ev idence for epidemic disease as an agent in the catastrophic decline of Australian rain forest frogs Conserv Biol 111026 29 Altig R Channing A 1993 Hypothesis functional signi cance of colour and pattern of anuran tadpoles Herpetol J 373 75 Andren C Henrikson L Olsson M Nil son G 1988 Effects of pH and aluminium on embryonic and early larval stages of Swedish brown frogs Rana arvalis R tem poraria and R dalmatina Holarctic Ecol 1 1 127 35 Anzalone CR Kats LB Gordon MS 1998 Effects of solar UV B radiation on embry onic development in Hyla cadaverina Hyla regilla and Taricha torosa Conserv Biol 12646 53 Amtzen JW Teunis SFM 1993 A six year study on the population dynamics of the GLOBAL AMPHIBIAN DECLINES 157 10 11 12 13 14 15 16 17 18 crested newt Triturus cristatus following the colonization of a newly created pond Herpetol J 399 1 10 Ash AN 1988 Disappearance of salaman ders from clearcut plots J Elisha Mitchell Sci Soc 104116 22 Ash AN 1997 Disappearance and return of Plethodontid salamanders to clearcut plots in the southern Blue Ridge Moun tains Conserv Biol 11983 89 Barinaga M 1990 Where have all the frog gies gone Science 2471033 34 Beattie RC TylerJones R 1992 The ef fects of low pH and aluminum on breed ing success in the frog Rana temporaria J Herpetol 26353 60 Beattie RC Tyler Jones R Baxter MJ 1992 The effects of pH aluminium con centration and temperature on the em bryonic development of the European common frog Rana temporaria J Zool London 228557 70 Beebee TJ 1977 Environmental change as a cause of Natterjack Toad Bufo calamita declines in Britain Biol Cons 1187 102 Beebee TJC 1995 Amphibian breeding and climate Nature 374219 20 Beebee TJC Denton JS Buckley J 1996 Factors affecting population densities of adult natterjack toads Bufo calamita in Britain J Appl Ecol 33263 68 Beebee TJC Flower RJ Stevenson AC Patrick ST Appleby PG et al 1990 De cline of the Natterjack Toad Bufo calamita in Britain paleoecological documentary and experimental evidence for breeding site acidi cation Biol Conserv 5321 20 Beiswenger RE 1986 An endangered species the Wyoming toad Bufo hemio phrys baxteri the importance of an early warning system Biol Cons 3759 71 Berger L Speare R Daszak P Green DE Cunningham AA et al 1998 Chytrid iomycosis causes amphibian mortality as sociated with population declines in the rain forests of Australia and Central Amer 19 20 21 22 23 24 25 26 27 28 ica Proc Natl Acad Sci USA 95 29031 36 Bertram S Berrill M 1997 Fluctuations in a northern population of gray treefrogs Hyla versicolor See Ref 87 pp 57 63 Berven KA 1990 Factors affecting popu lation uctuations in larval and adult stages of the wood frog Rana sylvatica Ecology 711599 1608 Berven KA Grudzien TA 1990 Disper sal in the wood frog Rana sylvatica im plications for genetic population structure Evolution 442047 56 Bishop CA 1992 The effects of pesticides on amphibians and the implications for de termining causes of declines in amphib ian populations In Declines in Canadian Amphibian Populations Designing a Na tional Monitoring Strategy ed CA Bishop KE Pettit pp 67 70 Occas Pap No 76 Can Wildlife Serv Blaustein AR 1994 Chicken Little or Nero s ddle A perspective on declining amphibian populations Herpetologica 50 85 97 Blaustein AR Edmund B Kiesecker JM Beatty JJ Hokit DG 1995 Ambient ul traviolet radiation causes mortality in sala mander eggs Ecol Appl 5740 43 Blaustein AR Hoffman PD Hokit DG Kiesecker JM Walls SD Hays JB 1994 UV repair and resistance to solar UV B in amphibian eggs a link to population de clines Proc Natl Acad Sci USA 91 1791 95 Blaustein AR Hoffman PD Kiesecker J M Hays JB 1996 DNA repair activity and resistance to solar UV B radiation in eggs of the red legged frog Conserv Biol 10 1398 1402 Blaustein AR Hokit DG O Hara RK Holt RA 1994 Pathogenic fungus contributes to amphibian losses in the Paci c North west Biol Conserv 67251 54 Blaustein AR Kiesecker JM Chivers DP Anthony RG 1997 Ambient UV B ra diation causes deformities in amphibian 158 ALFORD I RICHARDS 29 30 31 32 33 34 35 36 37 38 embryos Proc Natl Acad Sci USA 94 13735 37 Blaustein AR Wake DB 1990 Declin ing amphibian populations a global phe nomenon Trends Ecol Evol 5 203 4 Blaustein AR Wake DB Sousa WP 1994 Amphibian declines judging stability per sistence and susceptibility of populations to local and global extinctions Conserv Biol 860 71 Bradford DF 1989 Allotopic distributions of native frogs and introduced shes in high Sierra Nevada lakes of California impli cations of the negative effect of sh intro ductions Copeia 1989775 78 Bradford DF 1991 Mass mortality and ex tinction in a highelevation population of Rana muscosa J Herpetol 25174 77 Bradford DF Gordon MS Johnson DF Andrews RD Jennings WB 1994 Acidic deposition as an unlikely cause for am phibian population declines in the Sierra Nevada California Biol Conserv 69 155 61 Bradford DF Swanson C Gordon MS 1994 Effects of low pH and aluminum on amphibians at high elevation in the Sierra Nevada California Can J Zool 72 1272 79 Bradford DF Tabatabai F Graber DM 1993 Isolation of remaining populations of the native frog Rana muscosa by intro duced shes in Sequoia and King s Canyon National Parks California Conserv Biol 7882 88 Bradford DF Swanson C Gordon MS 1992 Effects of low pH and aluminum on two declining species of amphibians in the Sierra Nevada California J Herpetol 26369 77 Breckenridge WJ Tester JR 1961 Growth local movements and hibernation of the Manitoba toad Bufo hemiophrys Ecology 42637 46 Breden F 1987 The effect of post metamorphic dispersal on the population genetic structure of Fowler s toad Bufo 39 40 41 42 43 44 45 46 47 48 49 woodhouseifowleri Copeia 1987386 95 Brooks RJ 1992 Monitoring wildlife pop ulations in long term studies See Ref 22 pp 94 97 Brown WC Alcala AC 1970 Popula tion ecology of the frog Rana erythraea in southern Negros Philippines Copeia 197061 1 22 Bruce RC 1995 The use of temporary removal sampling in a study of popula tion dynamics of the salamander Desmog nathus monticola Aust J Ecol 20403 12 Buckley D Arano B Herrero P Llorente G 1996 Population structure of Moroc can water frogs genetic cohesion despite a fragmented distribution J Zool Syst Evol Res 342173 79 Bury RB Corn PS 1988 Responses of aquatic and streamside amphibians to tim ber harvest A review In Streamside Man agement Riparian Wildlife and Forestry Interactions ed KJ Raedeke pp 165 81 Seattle Univ Was Press Caldwell JP 1987 Demography and life history of two species of chorus frogs AnurazHylidae in South Carolina Copeia 1987 1 14 27 Caley MJ Carr MH Hixon MA Hughes TP Jones GP Menge BA 1996 Recruit ment and the local dynamics of open ma rine populations Annu Rev Ecol Syst 27477 500 Carey C Bryant CJ 1995 Possible inter relationships among environmental toxi cants amphibian development and decline of amphibian populations Environ Health Perspec 103Suppl 413 17 Carey CL 1993 Hypothesis concerning the causes of the disappearance of bo real toads from the mountains of Colorado Conserv Biol 7355 62 Chovanec A 1992 The in uence of tad pole swimming behaviour on predation by dragon y nymphs Amphibia Reptilia 13 341 49 Clay D 1997 The effects of temperature and acidity on spawning of the spotted GLOBAL AMPHIBIAN DECLINES 159 50 51 52 53 54 55 56 57 58 59 60 salamander Ambystoma maculatum in Fundy National Park See Ref 87 pp 226 32 Cohen MP 1995 Ecology of two popu lations of Bufo marinus in northeastern Australia PhD thesis James Cook Univ Townsville Australia 203 pp Corn PS 1994 What we know and don t know about amphibian declines in the west In Sustainable Ecological Systems Imple menting an Ecological Approach to Land Management ed LF DeBano WW Cov ington pp 59 67 Fort Collins CO USDA For Serv Rocky Mountain For Range Exp Station Corn PS Bury RB 1989 Logging in west ern Oregon responses of headwater habi tats and stream amphibians For Ecol Manage 2939 57 Corn PS Fogleman JC 1984 Extinction of montane populations of the Northern Leopard Frog Rana pipiens in Colorado J Herpetol 18147 52 Corn PS Stolzenburg W Bury RB 1989 Acid Precipitation Studies in Colorado and Wyoming Interim Report of Surveys of Montane Amphibians and Water Chem istry Biol Rep 80 US Fish amp Wildlife Serv pp 1 56 Corn PS Vertucci FA 1992 Descriptive risk assessment of the effects of acidic de position on Rocky Mountain amphibians J Herpetol 26361 69 Crawshaw GJ 1992 The role of disease in amphibian decline See Ref 22 pp 60 62 Crawshaw GJ 1997 Disease in Canadian amphibian populations See Ref 87 pp 258 70 Crump ML 1986 Homing and site delity in a neotropical frog Atelopus varius Bu fonidae Copeia 1986438 44 Cunningham AA Langton TES Bennett PM Lewin JF Drury SEN et al 1993 Un usual mortality associated with poxvirus like particles in frogs Rana temporaria Vet Rec 133141 42 Cunningham AA Langton TES Bennett 61 62 63 64 65 66 67 68 69 70 71 72 PM Lewin JF Drury SEN et al 1996 Pathological and microbiological ndings from incidents of unusual mortality of the common frog Rana temporaria Philos Trans R Soc Lond Ser B 3511539 57 Daugherty CH Sheldon AL 1982 Age speci c movement patterns of the frog As caphus truei Herpetologica 38468 74 Delis PR Mushinsky HR McCoy ED 1996 Decline of some west central Florida anuran populations in response to habitat degradation Biodiv Conserv 51579 95 Dodd CK Jr 1991 Drift fence associated sampling bias of amphibians at a Florida sandhills temporary pond J Herpetol 25 296 301 Dodd CK Jr 1992 Biological diversity of a temporary pond herpetofauna in north Florida sandhills Biodiv Conserv 1125 142 Dodd CK Jr 1994 The effects of drought on population structure activity and orien tation of toads Bufo quercicus and B ter restris at a temporary pond Ecol Ethol Evol 62331 49 Dole WJ 1965 Summer movements of adult leopard frogs Rana pipiens Schreber in northern Michigan Ecology 46236 55 Donnelly MA Crump ML 1998 Po tential effects of climate change on two neotropical amphibian assemblages Cli mate Change 39541 61 Dorn WMP Brandl R 1991 Local distri bution of amphibians the importance of habitat fragmentation Global Ecol Bio geogr Lett 136 41 Drost CA Fellers GM 1996 Collapse of a regional frog fauna in the Yosemite area of the California Sierra Nevada USA Con serv Biol 10414 25 Duellman WE Trueb L 1986 Biology of Amphibians New York McGrawHill 670 pp Dunson WA Wyman RL Corbett ES 1992 A symposium on amphibian declines and acidi cation J Herpetol 26349 52 Eagle P 1999 Amphibian Count Database 160 ALFORD I RICHARDS 73 74 75 76 77 78 79 80 81 82 83 84 United States Geological Survey http wwwmp2pwrcusgsgovampCVampdb cfm Elmberg J 1990 Longterm survival length of breeding season and operational sex ratio in a boreal population of common frogs Rana temporaria L Can J Zool 68 121 27 Elmberg J 1993 Threats to boreal frogs Ambio 22254 255 Fellers GM Drost CA 1993 Disappear ance of the cascades frog Rana cascadae at the southern end of its range California USA Biol Conserv 65 177 81 Fisher RN Shaffer HB 1996 The decline of amphibians in California s Great Central Valley Conserv Biol 101387 97 Fite KV Blaustein A Bengston L Hewitt HE 1998 Evidence of retinal light damage in Rana cascadae a declining amphibian species Copeia 1998906 14 Freda J Dunson WA 1986 Effects of low pH and other chemical variables on the local distribution of amphibians Copeia 1986454 66 Freda J Sadinski WJ Dunson WA 1991 Long term monitoring of amphibian popu lations with respect to the effects of acidic deposition Water Ail Soil Pollut 55445 62 Freedman B Shackell NL 1992 Amphib ians in the context of a national environ mental monitoring program See Ref 22 pp101 104 Friedl TWP Klump GM 1997 Some as pects of population biology in the Euro pean treefrog Hyla arborea Herpetolog ica 53321 30 Gamradt SC Kats LB 1996 Effect of introduced cray sh and mosquito sh on California Newts Conserv Biol 1021155 62 Gill DE 1978 The metapopulation ecol ogy of the redspotted newt Notoph thalmus viridescens Ra nesque Ecol Monogr 48145 66 Gittins SP 1983 Population dynamics of 85 86 87 88 89 90 91 92 93 94 the common toad Bufo bufo at a lake in midWales J Anim Ecol 52981 88 Grant KP Licht LE 1995 Effects of ul traviolet radiation on lifehistory stages of anurans from Ontario Canada Can J Zool 732292 306 Green DM 1992 Fowler s toads Bufo woodhousei fowleri at Long Point On tario changing abundance and implica tions for conservation See Ref 22 pp 37 43 Green DM 1997 Perspectives on amphib ian population declines de ning the prob lem and searching for answers In Am phibians in Decline Canadian Studies of a Global Problem ed DM Green pp 291 308 Herpetological Conserv Vol 1 Green DM 1997 Temporal variation in abundance and age structure in Fowler s toads Bufofowleri at Long Point Ontario See Ref 87 pp 45 56 Gyovai F 1989 Demographic analysis of the moor frog Rana arvalis olterstonj Feje rva ry 1919 population in Fraxino pannonicaeAlnetum of the Tisza basin T iscia Szeged 24 107 21 Hairston NG 1983 Growth survival and reproduction of Plethodon jordani trade offs between selective pressures Copeia 19831024 35 Hairston NG Sr Wiley RH 1993 No de cline in salamander AmphibiaCaudata populations a twenty year study in the southern Appalachians Brimleyana 18 59 64 Halley JM Oldham RS Arntzen J W 1996 Predicting the persistence of amphibian populations with the help of a spatial model J Appl Ecol 33455 70 Hanski I 1997 Metapopulation dynamics from concepts and observations to predic tive models In Metapopulation Biology Ecology Genetics and Evolution ed I Hanski M Gilpin pp 69 91 San Diego CA Academic Press 512 pp Hanski I 1998 Metapopulation dynamics Nature 39641 49 GLOBAL AMPHIBIAN DECLINES 161 95 96 97 98 99 100 101 102 103 104 105 106 Hanski I Pakkala T Kuussaari M Lei G 1995 Metapopulation persistence of an endangered butter y in a fragmented landscape Oikos 722128 Harte J Hoffman E 1989 Possible effects of acidic deposition on a Rocky Mountain population of the tiger salamander Am bystoma tigrinum Conserv Biol 3149 58 Hayes MP Jennings MR 1986 Decline of frog species in western North America are bullfrogs Rana catesbeiana respon sible J Herpetol 20490 509 Hays JB Blaustein AR Kiesecker JM Hoffman PD Pandelova I Coyle D Richardson T 1996 Developmental re sponses of amphibians to solar and arti cial UVB sources a comparative study Photochem Photobiol 64449 55 Hecnar SJ 1997 Amphibian pond com munities in southwestern Ontario See Ref 87 pp 1 15 Hecnar SJ M Closkey RT 1996 The effects of predatory sh on amphibian species richness and distribution Biol Conserv 79123 31 Hecnar SJ M Closkey RT 1996 Re gional dynamics and the status of amphib ians Ecology 772091 97 Hecnar SJ M Closkey RT 1997 Changes in the composition of a ranid frog com munity following bullfrog extinction Am Midl Nat 137145 50 Hecnar SJ M Closkey RT 1997 Spatial scale and determination of species status of the green frog Conserv Biol 11670 82 Henrikson BI 1990 Predation on am phibian eggs and tadpoles by common predators in acidi ed lakes Holarctic Ecol 13201 6 Herman TB Scott FW 1992 Assessing the vulnerability of amphibians to cli matic warming See Ref 22 pp 46 49 Hero J M Gillespie GR 1997 Epidemic disease and amphibian declines in Aus tralia Conserv Biol 111023 25 107 108 109 110 111 112 113 114 115 116 117 118 Heyer WR 1979 Annual variation in lar val amphibian populations within a tem perate pond J Wash Acad Sci 6965 74 Homolka M Kokes J 1994 Effect of air pollution and forestry practice on the range and abundance of S alamandra sala mandra Folia Zoologica 4349 56 Horne MT Dunson WA 1994 Exclu sion of the Jefferson salamander Am bystoma je ersonianum from some po tential breeding ponds in Pennsylvania effects of pH temperature and metals on embryonic development Arch Environ Contamination Toxicol 27323 30 Horne MT Dunson WA 1995 Effects of low pH metals and water hardness on lar val amphibians Arch Environ Contami nation Toxicol 29500 5 Husting EL 1965 Survival and breeding structure in a population of Ambystoma maculatum Copeia 1965352 59 Ishchenko VG 1989 Population biology of amphibians Sov Sci Rev E Physiol Gen Biol 3119 55 J aeger RG 1980 Densitydependent and densityindependent causes of extinction of a salamander population Evolution 34 617 21 Jennings MR Hayes MP 1994 Decline of native ranid frogs in the desert south west In Southwestern Herpetol Soc Spec Publ No 5 ed PR Brown JW Wright pp 183 211 J oglar RL Burrowes PA 1996 Declining amphibian populations in Puerto Rico In Contributions to West Indian Herpetol ogy A Tribute to Albert Schwartz ed R Powell RW Henderson pp 371 80 SSAR Contrib to Herpetol Volume 12 Johnson B 1992 Habitat loss and declin ing amphibian populations See Ref 22 pp71 75 Kagarise Sherman C Morton ML 1993 Population declines of Yosemite toads in the eastern Sierra Nevada of California J Herpetol 27186 98 Kats LB Petranka JW Sih A 1988 162 ALFORD I RICHARDS 119 120 121 122 123 124 125 126 127 128 129 Antipredator defenses and the persistence of amphibian larvae with shes Ecology 69 1865 70 Kerr J B McElroy CT 1993 Evidence for large upward trends of ultravioletB radi ation linked to ozone depletion Science 262 1032 34 Kiesecker JM Blaustein AR 1995 Syn ergism between UV B radiation and a pathogen magni es amphibian embryo mortality in nature Proc Natl Acad Sci USA 92 1 1049 52 Kiesecker JM Blaustein AR 1997 Pop ulation differences in responses of red legged frogs Rana aurora to introduced bullfrogs Ecology 78 1752 60 Kiesecker JM Blaustein AR 1998 Ef fects of introduced bullfrogs and small mouth bass on microhabitat use growth and survival of native redlegged frogs Rana aurora Conserv Biol 12776 87 Koonz W 1992 Amphibians in Mani toba See Ref 22 pp19 20 Kucken DJ Davis J S Petranka JW Smith KC 1994 Anakeesta stream acidi cation and metal contamination effects on a salamander community J Environ Qual 23 131 1 17 Kuzmin S 1994 The problem of declin ing amphibian populations in the Com monwealth of Independent States and ad jacent territories Alytes 12 123 34 Laan R Verboom B 1990 Effects of pool size and isolation on amphibian commu nities Biol Conserv 54251 62 Lannoo MJ Lang K Waltz T Phillips GS 1994 An altered amphibian assemblage Dickinson County Iowa 70 years after Frank Blanchard s survey Am Midl Nat 131 31 1 1 9 Laurance WF 1996 Catastrophic de clines of Australian rainforest frogs Is unusual weather responsible Biol Con serv 77203 12 Laurance WF McDonald KR Speare R 1996 Epidemic disease and the catas 131 132 133 134 135 136 137 138 139 trophic decline of Australian rain forest frogs Conserv Biol 10406 13 130 Licht LE Grant KP 1997 The effects of ultraviolet radiation on the biology of am phibians Am Zool 37137 45 Lips KR 1998 Decline of a tropical montane amphibian fauna Conserv Biol 12106 17 Lizana M Pedraza EM 1998 The effects of UV B radiation on toad mortality in mountainous areas of central Spain Con serv Biol 12703 7 Long LE Saylor LS Soule ME 1995 A pHUVB synergism in amphibians Con serv Biol 91301 3 Martof B 1956 Factors in uencing the size and composition of populations of Rana clamitans Am Midl Nat 56224 45 McDonald KR Alford RA 1999 A review of declining frogs in northern Queensland In Declines and Disap pearances of Australian Frogs National Threatened Frog Workshop 1997 ed A Campbell Canberra Environment Aus tralia In press Meyer AH Schmidt BR Grossenbacher K 1998 Analysis of three amphibian populations with quartercentury long time series Proc R Soc Lond Ser B 523 28 Mierzwa KS 1998 Status of northeastern Illinois amphibians In Status and Con servation of Midwestern Amphibians ed MJ Lannoo pp 115 24 Iowa City Univ Iowa Press Nagle MN Hofer R 1997 Effects of ul traviolet radiation on early larval stages of the Alpine newt Triturus alpestris un der natural and laboratory conditions 0e cologia 110514 19 Nee S May RM Hassell MP 1997 Twospecies metapopulation models In Metapopulation Biology Ecology Ge netics and Evolution ed I Hanski M Gilpin pp 123 47 San Diego CA Aca demic Press 512 pp GLOBAL AMPHIBIAN DECLINES 163 140 141 142 143 144 145 146 147 148 149 150 151 Nicholls N 1984 A system for predict ing the onset of the north Australian wet season J Climatol 4425 35 Nyman S 1986 Mass mortality in lar val Rana sylvatica attributable to the bac terium Aeromonas hydrophilum J Her petol 202196 201 Olson DH 1989 Predation on breed ing western toads Bufo boreas Copeia 1989391 97 Ovaska K 1997 The vulnerability of am phibians in Canada to global warming and increased solar radiation See Ref 87 pp 206 25 Ovaska K Davis TM Flamarique IN 1997 Hatching success and larval sur vival of the frogs Hyla regilla and Rana aurora under ambient and arti cially en hanced solar ultraviolet radiation Can J Zool 751081 88 Oza GM 1990 Ecological effects of the frog s legs trade Environmentalist 1039 41 Pechmann J HK Scott DE Semlitsch RE Caldwell JP Vitt LJ Gibbons JW 1991 Declining amphibian populations the problem of separating human impacts from natural uctuations Science 253 892 95 Pechmann JHK Wake DB 1997 De clines and disappearances of amphibian populations In Principles of Conserva tion Biology ed GK Meffe CR Carroll pp 135 37 Sunderland MA Sinauer 2nd ed Pechmann JHK Wilbur HM 1994 Putting declining amphibian populations in perspective natural uctuations and human impacts Herpetologica 5065 84 Petranka JW Eldridge ME Haley KE 1993 Effects of timber harvesting on southern Appalachian salamanders Con serv Biol 71363 70 Pierce BA Wooten DK 1992 Genetic variation in tolerance of amphibians to low pH J Herpetol 26422 29 Portnoy JW 1990 Breeding biology of 152 153 154 155 156 157 158 159 160 161 the spotted salamander Ambystoma mac ulatum Shaw in acidic temporary ponds at Cape Cod USA Biol Conserv 5361 75 Pounds JA Crump ML 1994 Amphib ian declines and climate disturbance the case of the golden toad and the harlequin frog Conserv Biol 872 85 Pounds JA Fogden MPL Savage JM Gorman GC 1997 Tests of null mod els for amphibian declines on a tropical mountain Conserv Biol 111307 22 Power T Clark KL Harfenist A Peakall DB 1989 A review and evaluation of the amphibian toxicological literature Tech Rep 61 Can Wildlife Serv Preest MR 1993 Mechanisms of growth rate reduction in acid exposed larval sala manders Ambystoma maculatum Phys iol Zool 66686 707 Ramirez J Vogt RC Villareal Benitez JL 1998 Population biology of a neo tropical frog Rana vaillanti J Herpetol 322338 44 Ramotnik CA 1997 Conservation As sessment of the Sacramento Mountain Salamander Gen Tech Rep RMGTR 293 Fort Collins CO USDAFS Rocky Mountain For Range Exp Stat Raymond LR 1991 Seasonal activity of Siren intermedia in northwestern Loui siana Amphibia Sirenidae Southwest ern Nat 36144 47 Raymond LR Hardy LM 1990 De mography of a population of Ambystoma talpoideum Caudata Ambystomatidae in northwestern Louisiana Herpetologica 462371 82 Raymond LR Hardy LM 1991 Effects of a clearcut on a population of the mole salamander Ambystoma talpoideum in an adjacent unaltered forest J Herpetol 25509 12 Reading CJ Loman J Madsen T 1991 Breeding pond delity in the common toad Bufo bufo J Zool Lond 225 201 1 1 164 ALFORD I RICHARDS 162 163 164 165 166 167 168 169 170 171 172 173 Reed JM Blaustein AR 1995 Assess ment of nondeclining amphibian pop ulations using power analysis Conserv Biol 921299 1300 Richards SJ McDonald KR Alford RA 1993 Declines in populations of Aus tralia s endemic tropical rainforest frogs Paci c Conserv Biol 166 77 Sarkar S 1996 Ecological theory and anuran declines BioScience 46199 207 Schlupp I Podloucky R 1994 Changes in breeding site delity a combined study of conservation and behaviour in the common toad Bufo bufo Biol Con serv 69285 91 Schwalbe CR Rosen PC 1988 Prelimi nary report on effect of bullfrogs on wet land herpetofaunas in southeastern Ari zona In Management of Amphibians Reptiles and Small Mammals in North America pp 166 73 US Dep Agric Semlitsch RD 1998 Biological delin eation of terrestrial buffer zones for pond breeding salamanders Conserv Biol 12 1 1 13 1 9 Semlitsch RD Bodie JR 1998 Are small isolated wetlands expendable Conserv Biol 121129 33 Semlitsch RD Scott DE Pechmann J HK Gibbons JW 1996 Structure and dynam ics of an amphibian community In Long Term Studies of Vertebrate Communities ed ML Cody JA Smallwood pp 217 50 San Francisco Academic Press Shirose LJ Brooks RJ 1997 Fluctua tions in abundance and age structure in three species of frogs Anura Ranidae in Algonquin Park Canada from 1985 to 1993 See Ref 87 pp 16 26 Shoop CR 1974 Yearly variation in lar val survival of Ambystoma maculatum Ecology 55440 44 Sinsch U 1991 Minireview the orien tation behaviour of amphibians Herpetol J 1541 44 Sinsch U 1992 Structure and dynamics 174 175 176 177 178 179 180 181 182 183 of a natterj ack toad metapopulation Bufo calamita 0ecologia 90489 99 Sinsch U 1996 Population dynamics of natterjack toads Bufo calamita in the Rhineland a nineyears study Verh Deutschen Zool Ges 891 127 Sjogren P 1991 Extinction and isolation gradient in metapopulations the case of the pool frog Rana lessonae Biol J Linn Soc 422135 47 Sjogren Gulve P 1994 Distribution and extinction patterns within a northern metapopulation of the pool frog Rana lessonae Ecology 75 1357 67 Sredl MJ Collins EP Howland JM 1997 Markrecapture of Arizona leopard frogs In Ranid Frog Conservation and Manage ment Nongame and Endangered Wildl Prog Tech Rept 12 Ariz Game Fish Dept ed MJ Sredl pp 1 20 Stebbins RC 1954 Natural history of the salamanders of the Plethodontid genus Ensatina Univ Calif Publ in Zool 54 47 124 Stromberg G 1995 The yearly cycle of the jumping frog Rana dalmatina in Sweden A 12 year study Scientia Her petologica 1995185 86 Stumpel AHP 1987 Distribution and present numbers of the tree frog Hyla ar borea in Zealand Flanders The Nether lands Amphibia Hylidae Bijdragen tot de Dierkunde 57 151 63 Taub FB 1961 The distribution of the redbacked salamander Plethodon c cinereus within the soil Ecology 42681 98 Terhivuo J 1988 Phenology of spawning of the common frog Rana temporaria in Finland from 1846 to 1986 Ann Zool Fennici 25 165 75 Toft CA Rand AS Clark M 1982 Popu lation dynamics and seasonal recruitment in Bufo typhonius and Colostethus nubi cola Anura In The Ecology of a Tropi cal Forest Seasonal Rhythms and Long Term Changes ed EG Leigh Jr AS Rand Am phibian ivation amp Hibern me gt Introduction amp definition gt Estivation gt Hibernation or Overwintering gt Supplement reading 77 Global Diversity at Amphlblan Samar i 3 s I 1 a a f a y A gi 5mm Ihclhmli iikvlluzawz Amphibian occurs in wide range over the world 3 Main challenges to survival 0 Starvation Cold Hibernation IDrought Estivation mm breeding or active period while conserving as many as resources as possiblequot minimum Estivation a state ofreduce metabolism periodically dry habitats and become inactive Hibernation or OvenNintering a state of reduce metabolism seen most ommony in anurans inhabiting cold environments however ms may mean a state of controlled torpor w mammahan physwologwst Other words Dormancy Torpor Brumation E lln slioiry Estiaors General behavior and ecology Highly terrestrial Nocturnal and fossorial Spend 710 months year for Estivation Eggs and Larva develop quickly Can occur several months when condition are favorable lililm him Adult anurans that inhabits in xeric area or area which prolonged drought which surface water is disappeared Most of them aestivate in burrow r 41 WNW Scaphiopus couchii currents 9 act ut Notaden melanoscaphus Scaghiopus hammondii u in illilli 61 mm Some aquatic amph bians such as anurans and salamanders This group do estivation in mud or build cocoon er op ys orna a Xenopus laevis Larva of some salamanders m 39 39 39 9 Cue for entering and breaking of estivation Rain and High Humidity Photoperiod Temperature The ability to estivate during periods of adverse condition allows some anuran to survive in truly extreme environment iii row lllll li li lf lil lf ll Tne rnost important pnvsioai variabies on burrows are Temperature much luvver and less variable than surface Huweveri variabie may occur depending on seasuri depm geograpni lucatiuri and soii types Soil water tension is functiun Elf Water ument paricle size and SEIll nernistry Concentration of respiratory gases depend on rEspiraIiEIri or estivatorand otnerorganisrns in around arnpnibian borrows MW W Nun randorniv distribution osoaiiv in area vvnien snaiiovv vvatertabie orvvnere soii muisture eioser in sonaee Burrow selection oiiaoi pia i iooii wniie addati es ivator nas iittie noice example in Scapniopos average borrovv deptn in raii around in ern reaen to 5mm ern in midWiritEr Geo 3 types multiple layers of shed stratum single stratum of corneum and a layer of secreted reduced water loss and evaporate found in Lepidobatrachus IIanensis Ceratophrys ornate Pyxicephalus adspems and also in Siren intermedia cocoon derived 39om mucus for example M Elee ml Hamlets Mphibians still continue their metabolism during will harm to life During estivation plasma urea of Scaphiopus couchiiincreasing to 200300 mM This concentration may help to maintain water uptake from moisture soil but will denature proteins and disturb enzymes activities ln anurans counterbalance ofthis substance by trimethylamine oxide betaine and sarcosine g l with sufficient reserves to breed take decreases to 30 l m Clt 02 ka39 q 7V ofJeSlmg Within 3 hrs 1 alteration or enzymeprorerh acher 2 changes h the subcellular location or enzymes 3 regulation or the anabolic uses or carbohydrate fl Amph bians reserve their fuel in term of triglyceride which found in abdominal fat body and lipids which found in liver and other organs Just before estivation the fat bodies represent about 3 45 if body mass although it may be extremely variables Carbohydrate will use at I h39 x Start Of estivation R x XX quot v Major energy source is fat as body I a Protein is used at the end a of extreme estivation HibernalinWellinterim Ftquot Northern limits of some Northern American Amphibians t all 4 q z39 y r if 39 quot 1 t quot 39 39 quot lei f Plath0101 f I Itinerqu J i g Dunn r 11 us 39I vuicrascnns mg to dl and t m To survive over prolong cold and starvation hibernators will use same basic strategies a accumulation of fuel reserves prior to winter b adjustments to cellular membranes and proteins to optimize low temperature function mtmtet mg llt ctmv mimemt 3 strategies for overwintering Underwater hibernators will save from freezing but may suffered from anoxia or hypoxia 0 predators Terrestrial hibernators will save from predators or predators but may frost under severe weather Burrowers hibernators may safer but may challenged with freezing thteir tt irt ali ty May reaching 50 of population of Pethodon cinereus and Eurycea bilineata Vernberg 1953 High mortal rate may episodic rather than routine ln aquatic animals usually concern with anoxia ial lillm Useful Options to survive in cold weather are a avoid to expose subzero temperature or b to tolerate 39eezing point Most terrestrial amphibian choose avoidance strategy but some Rana sylvatica Hyla versicolor H cruder and Pseudacris triseriatachoose to tolerate ice formation in extracellular uid space To avoid subzero temperature Finding wellaerated stable temperature and moist hibenacula Have stored enough reserved energy To tolerate subzero temperature Biochemical adaptation for tolerate exing control of extracellular ice regulation of cell volume protection of subcellular organization viability in the 39ozen state m pir Key substance for cryoprotectant and dimethylsulfoxide are equally effective Mi YIIIIIIEIIHII mu zucumulzllnn n1 hy mums m Rana symnca synenca
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