—— Great Basin Naturidist52{3),pp.262-26S POST-PLEISTOCENE DISPERSAL IN THE MEXICAN VOLE {MICROTUS MEXICANUS): AN EXAMPLE OF AN APPARENT TREND IN THE DISTRIBUTION OF SOUTHWESTERN MAMMALS Russell Diuis' cUiclJ. R. Calkhan" — ABSTR-Kcrr. The present distribution ofthe Mexican \ole {Micwtiis mcxicanits) is not entirely the product ofpost- Pleistoceneforestfragmentationandextinction;recentdispersalalsoisindicated. Literature records furthersuggestthat thisphenonient)n nia\-reflectageneralpatternofnorthwardlangeexpansioninmanysouthwestern mauuual species. Kx-i/iionl.s: Microtns.vole,dispersal,hi()<ê()î-(ij)liy. vieaiitiitce. Pleistocene. Traditional hiogeographic tlieon attributes DISPERSAL: A BRIKF RK\1E\\ tlie niodeni distribution of small, nonll)ing niontant^ niamnials in the Southwest to post- Post-Pleistocene dispersal has been \erified Pleistoceneclimaticchange(Brown 1971, 1978, primarily in (1) conspicuous, diurnal mammals Patterson 1984, Patterson and Atmar 1986). such as sciurids and (2) mammals colonizing Restriction of woodland and forest habitat to regions that were previously well sampled by higher elexâtions is assumed to have stranded collectors. For species and groups that do not sucli species on isolated patches of montane fall into either categorv, the biogeographer is habitat. Although it is recognized that local left to interpret broader distribution patterns extinction has caused further range reductions, ancPorsmall bits ofindirect evidence. post-Pleistocene range expansion generalK'has As an example of the first situation, Davis beendiscoimted(Brown 1971, 1978).Thisrelict and Browii (1989) and Davis and Bissell (1989) model satisfactorih' explains the distribution of showed that recent dispersal has significantly many Great Basin species, but evidence from altered the distribution of Aberts squirrel else\\'here in the Southwest strongK' supports iSciunis abciii). Another example involves the recent dispersal (Da\is and Dunford 1987, duskv chipmunk {Tamias ohscunis), which was Daxis and Ward 1988, Da\is et al. 1988, Daxis absentfromThomas MoimtaininsouthernCal- and Bissell 1989, Daxis and Brown 1989, ifornia at least between 1974 and 1976 (Calla- Lomolino et al. 1989). han 1977). Bv 1979the species hadrecolonized In this paper we will review exidence indi- thispeak,which isisolatedfromthe San facinto cating that manv southwesteni nuunmals range bv a lO-mile stretch of semiarid grass- including the Mexican xole andother montane lancPsagebrush habitat (Callahan, in prepara- mammals, as well as nonmontane species tion).ThesecondscenarioisillustratedbvDavis have shown a striking northward range shift and Dunford (1987) and Davis and Ward during the past sexeral decades. For some spe- (1988), who foundevidence ofrecent montane cies this pattern appears to reflect mildei- win- colonization by Signiodon ochrog^nathus in a tersorhuman influences; forothersthetrendis well-studied areaofsoutheastArizona. hardertoexplain. Ifxerified,howe\(M-,thistrend Since manv small mammals are not readily presupposes(amongotherthings)agreaterdis- trapjx'dand manv localities have not l)eensam- spemraslallmcaampambaillist.y- than is txpicalK attributed to pled extensivc'lv, it is easv for critics to "shoot down" newdistribution records on the grounds of inadequate priorsampling. Insuch cases itis ^ni-piirtiiifiitpicall\ centralArizonaandonisolatedmountainstothe nhabits meadows in ponderosapineand mixed south, southwest, and north (Figs. 1. 2). Four •ouiter forests, but can occup\- pimon-jimiper populations occm- on mountains connected to woodland if suitable understoiv is present the central high countn In pimon-juniper Harris 1985, Hoffmeister 1986).'in Arizona it woodland and interior chaparral (Brown and 'ccurslessoftenininteriorchaparral andCir(>at Lowe 1983), through which the species could iasin desertscrub (Hoffmeister 1986). (lis[)er,se: the Nantanes Plateau, the Sierra The late Pleistocenedistributionofthisspe- Ancha,the BradshawMoimtains,andtheSouth iesprobablywascontinuousfrom the Mexican Kaibab (Fig. 2). Three otherpopulations occur lateau to the southwest U.S. (Findle\- and at sites that are isolated b\- grasslands but 264 Great Basin Naturalist [\V)Iuiiie 52 1986). Recent dispersal is not the onK possible explanation for this pattern, but it is the most parsimonious one; ancient relicts in dissimilar habitats would be expected to show more e\i- dence of di\'ergence after sexeral thousand vears. There is exidence ofa recent range expan- sioninnortheastArizona.The Mexicanvolewas firstrecordedintheNavajoMountainsinsouth- ern UtahandnorthernArizonain 1933(Benson 1935). Although this locality seems isolated, since 1986 the .species has turned up at se\eral other sites on Black Mesa in northeast Arizona (Spicer 1987).Thesesitesfallonalinesoutheast from Na\ajo Mountain to the southwest foot- liills of the Chuska Mountains. At Black Mesa(Fig. 2) thehabitatispin\'on- juniper, with ponderosapines and a few Doug- las-firs on north-facingslopes, draws, andother lOOkm protected areas (Spicer 1987). Again, this is relati\el\' poor habitat for this species, and it seems unlikeK' that the population could have in NF'"ti'g.w3M.eDxeitcaoilsanodl t.hseouctlhiestrrnihCiiotliooiiraodtoMischroowtiiinsgisiuo'mxiecaniisto\- siuvivedin isolation for sexeral thousand\ears. latedpopulations(modifiedIVom Findlevetal. 1975;some Between these sites and Naxajo Mountain is data from Hall I9S1). Open eireles indicate records listed mostlv pinyon-juniper, with narrow strips of bvFinlevetal. (1986). northerngrasslandandGreatBasindesertscrub (Browii and Lowe 1983). The Mexican \ole interconnected hy pinNon-jnniper woodland occupies these habitats elsewhere and presum- and interior cliaparral: Pro.spect \alle\, the abl\ can disperse through them. This scenario Music Monntains, and the llnala[)ai Monntain.s implies that the Chuska Mountains, now unoc- (Fig. 2). cupied bv the species (Hoffmeister 1986), will Since -lif iiualapai Monntain.s and Prospect eventualK' be colonized (or recolonized) from X'alley still contain small ])atches ol' forest, the the northwest. vole populations at these sites might be E\'idenc:e from NewMe.mcoandColo- — Plei.stocene relicts in Forest refugia. Bnt the rado. Findle\etal. (1975)suggestedthatthe population in the Music Mountains, a site range of Microtus iiwxicaniis in New Mexico midwaybet\veen theothertwo, consists ofOnK- could lia\e expanded as a result of recent dis- pinyon-juniper woodland (Sjîcer ot al. 19S5). })ersal. In the Sandia Mountains, trappingfrom Tliis habitat interconnects all three l()caliti(>s 1950 to 1970 re\ealed onl\- M. hnîicaudus. andis morelikelytoseneasadispersalcorridor Mexicanxoleswerefirsttakentherein 1970and than as a post-Plei.st(X-ene refnginm. The spe- soon became the dominant species. While the cieswas recordedin the Uualapai Mountains in speciescouldha\ebeenoverlookedearlier, dis- 1923 and in Prospect \'alleyin 1913, but it was persal from the Manzano Mountains (Fig. 3) is not found in the Mu.sic Mountains until 1981 anecuuilK'likel\-scenario. Until 1975thesewere (Spiceretal. 1985). the northernmost records east of the Rio When the rate of dispersal exceeds that of (wandeRi\erinNewMexico.TheMexicanvole extinction, aspecies shouldbepresenton those has since been recorded from five sites in luontaneislandsclosesttothe.source, assuming extremenortheastNewMexico(Dakjuest 1975, the species can cross the intenening habitat Finlex-et al. 1986). (Mac.VrthurandWilson 1967). The distiibution In C>olora(k) the first .specimens were taken ofthe Mexican xole in the Southwest generalK in 1956 at Mesa Verde (Rodeck and Anderson fitsthis model (Fig. 2; Lomolinoetal. 1989). In 1956). Later the species was found at seven Arizona tlie most closely relatedi.solate popula- more(Coloradosites (Fig. 3; MellottandChoate tionsoccurin geographicjiroximitx (Hofhuc>ister 1984, Finle\ et al. 1986). \ trapping studv in ! 19921 \'()i.i". DisrKP.SM. 265 'l^vm.l-: 1. Sontlirniinaiiniialsprcicslorwhiclithereise\init(>(ij)\ iit('iial(>iilii/lltits iiivxicdiiiis \arions in .Arizona; N in Thisstudv .New .Mexico into S Colo- rado ^dsiidUdsUd N\\ in Arizona ;uh1 per- Not reportedbveiirlvexplorers(Davis 1982);not hapsin .NewMexico recorded in .Arizona until 1892, in extreme S (HoffincMster 1986); no late Pleistocene record (Harris 19.85. Tabor 1940); Wallmoand Gallizioli (1954):butseeKaufmannetal. (1976) 'onrpatiismcsolcunis N\\'in Arizona 1;recentrecords(Hoflmeister 1986) njds.su Idjdcii N in Arizona and New IndiannameforpeccarvisofSpanishorigin(Sowis .Mexico 1984); rarelv encountered bv early explorers (Davis 1982); nousebvearlvprehistoriccultures (Crosswhite 1984, Sovvls 1984) I . 266 Ghkat Basin Naturalist [\olunie 52 1938, andothers priorto 1975, found no Mexi- the first such events tliat havebeenrecordedin can\-olesnearCimarron, NewMexico,although theliterature. Iftheseanimalswereabletocross otlier\olespeciesweretaken (Armstrong 1972, unsuitable habitat once, then thev could have Findlev et al. 1975). The Mexican vole is now done so repeatedl)'in the course of centuries. common in tlie area (Finley et al. 1986); dius, Our suggestion of recent dispersal bv the the northward range expansion by this species Mexicanvoleshouldbeevaluatedinthecontext ma\- he continuing into nottfieast New Mexico of a more general pattern involving manv andsoutheast Colorado. mammalspecies. Post-Pleistocenedispersalhas influenced montane species assemblages Discussion and Conclusions throughout much ofthe Southwest (Lomolino et al. 1989). In addition, we propose a second pattern of recent northward range expansion The historical legacy hypothesis requires involving at least 19 North American mammal widespread late Pleistocene distribution. The species, all primarily austral in distributicMi but pforsesislenrceecoorfdMdioccruotmuesntnswxtihceainlaitse iPnlejiosutotcheenme occupyingawide range ofhabitats (Table 1). New Mexico, adjacent portions of Texas, and This pattern of northward dispersal is not (perhaps)southeastArizona. Despitetheadmit- easily exjolained, and there is unlikelv to be a single causative factor. For some species, the tedlv weak fossil record, however, there is no shift appears to result from climatic change evidence that the species' range formerly includedtheentireareawherepopulationsnow and/orhabitatmodificationb)'humans.Alterna- tively, the pattern can be viewed as one smiill, exist (Harris 1985). Sex'eral lines of e\idence reconiizable northward surtje in a continuincr support post-Pleistocene dispersal lor this Holocene c>cle of nortli/south distribution species: shifts. 1 Distance as a predictor of pres- ence/absence (Lomolino et al. 1989). ACKNOWLEDCMENTS 2. Tlu^ clo.se relationship of adjacent Ari- zona populations, isolated bv theoreti- Preliminaiv drafts of the manuscript were calK'crossable habitat. read bv R. Sidner, M. V. Lomolino, and E. L. 3. Itspresencein isolatedhabitats unlikeK Cocknun. T \'an Devenderand an anonvnnous to have served as post-Pleistocene reviewer also provided helpful comments. refugia. Some ofthe fieldwork cited was conducted by 4. Recent records suggesting dispersal in R. B. Spicer and C. LaRue with support from n(nlh\\'est and northeast Arizona, cen- the Arizona Department of Game and Fish. tral and northeast New Mexico, and southern (Colorado. Literature Cited Although the distribution of the Mexican xole undoubtedly has been influenced by historical AkmsiiioNc, D. M. 1972. DistributionofmammdsinCol- events and by local extinctions, it is difficult to orado. Uni\ersit\' of Kans;is Museum ofNatunJ His- ignoretheevidenceofpastandcontinuingpost- toid Monograpli.3: 1-41.5. Pleistocene dispersal. Ai.LF.aXn,d|.M.e\.xi1cS9o5,.mOandeacbo\lleMert.iWon.oWf.iiPiraiiicien,iawlsitfhrofmielAdrinzootnesa Areviewerofthispaperaskedwin'the Mex- In-thecollector. BulletinoftheAmericiUi Museumol ican vole and other small mammals took 4()()() Natural llistoiyT: 19.3-258. years to reach certain localities that w(^ claim Bknson, S. B. 19.35.\biological recoun;ussanceofNavajo were colonized within the past few decades. Mountain. Utah. Uni\ersit\ of California Publications inZoolo(T\ 40:4.39-4.56. This point re(juires clarification. First, there Bhow\. D.E.,andC. H.LowE. 19-of.AiizonaPress,Tucson,iuidArizonaDepartment TheMuseum,TexasTech Uni\ersit\. ofGameandFish.602pp. CocKRUM. E. L. 19.52. MammalsofKansas. L'niversihol lloi.i.ANDEK. R.R., B. N.Hl( Ks and KSci DOw 1990. J. KansasPublicationsoltheMuseumof Natural Iliston Distributiond records ofthe\ellov\-nosed cotton rat, 7: 1-.303. Sit^modonocJiro^^nathus BailewinTexas.TexasJournal 19.56. New genus and species, Iclioiiijcteiis plii/l- ofScience42: 101-102. loti.s, recorded from the United States. Journal ot HiMlMlREY. S. R. 1974. Zoogeograplnofthe nine-bcmcK-d Manunalogv37:.546-.547. armadillo (Dasi/jxis novcmciiictits) in the United . 1960.Therecentmammalsol .\rizona:theirtaxon- States. BioScience24:457ff. omy and distribution. L'ni\ersit\ of .Arizona Press. |()NES. J. K.,Jr 1960. The hispid cotion rat in Nebraska. 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POST-PLEISTOCENE DISPERSAL IN THE MEXICAN VOLE (MICROTUS MEXICANUS): AN EXAMPLE OF AN APPARENT TREND IN THE DISTRIBUTION OF SOUTHWESTERN MAMMALS

Similar POST-PLEISTOCENE DISPERSAL IN THE MEXICAN VOLE (MICROTUS MEXICANUS): AN EXAMPLE OF AN APPARENT TREND IN THE DISTRIBUTION OF SOUTHWESTERN MAMMALS