Habitat selection of the desert night lizard Xantusia ... · ecosystem processes. Habitat selection...
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CEC Research | https://doi.org/10.21973/N3GM2M Fall 2017 1/6 Habitat selection of the desert night lizard (Xantusia vigilis) on Mojave yucca (Yucca schidigera) in the Mojave Desert, California Kirsten Boylan 1 , Robert Degen 2 , Carly Sanchez 3 , Krista Schmidt 4 , Chantal Sengsourinho 5 University of California, San Diego 1 , University of California, Merced 2 , University of California, Santa Cruz 3 , University of California, Davis 4 , University of California, San Diego 5 ABSTRACT The Mojave Desert is a massive natural ecosystem that acts as a biodiversity hotspot for hundreds of different species. However, there has been little research into many of the organisms that comprise these ecosystems, one being the desert night lizard (Xantusia vigilis). Our study examined the relationship between the common X. vigilis and the Mojave yucca (Yucca schidigera). We investigated whether X. vigilis exhibits habitat preference for fallen Y. schidigera log microhabitats and what factors make certain log microhabitats more suitable for X. vigilis inhabitation. We found that X. vigilis preferred Y. schidigera logs that were larger in circumference and showed no preference for dead or live clonal stands of Y. schidigera. When invertebrates were present, X. vigilis was approximately 50% more likely to also be present. These results suggest that X. vigilis have preferences for different types of Y. schidigera logs and logs where invertebrates are present. These findings are important as they help in understanding one of the Mojave Desert’s most abundant reptile species and the ecosystems of the Mojave Desert as a whole. INTRODUCTION Habitat selection is an important factor in the shaping of an ecosystem. Where an animal chooses to live and forage can affect distributions of plants, predators and prey, and can influence ecosystem processes. Habitat selection usually occurs at smaller, local scales (Penalver-Alcazar et. al. 2016). This is a significant concept in harsh environments with limited resources, such as the Mojave Desert in California. The Mojave Desert has extreme temperature fluctuations, ranging from below freezing to over 134.6 degrees Fahrenheit (Schoenherr 2017). It is also extremely dry, with less than 10 inches of rain per year on average (Schoenherr 2017). Because of these harsh climatic characteristics, species that inhabit this region often have specific habitat requirements and preferences in order to survive (Schoenherr 2017).
Transcript of Habitat selection of the desert night lizard Xantusia ... · ecosystem processes. Habitat selection...
CEC Research | https://doi.org/10.21973/N3GM2M Fall 2017 1/6
Habitatselectionofthedesertnightlizard
(Xantusiavigilis)onMojaveyucca(Yuccaschidigera)intheMojaveDesert,California
KirstenBoylan1,RobertDegen2,CarlySanchez3,KristaSchmidt4,ChantalSengsourinho5
UniversityofCalifornia,SanDiego1,UniversityofCalifornia,Merced2,UniversityofCalifornia,SantaCruz3,UniversityofCalifornia,Davis4,
UniversityofCalifornia,SanDiego5
ABSTRACT
TheMojave Desert is a massive natural ecosystem that acts as a biodiversityhotspot for hundreds of different species. However, there has been littleresearchintomanyoftheorganismsthatcomprisetheseecosystems,onebeingthe desert night lizard (Xantusia vigilis). Our study examined the relationshipbetween the common X. vigilis and theMojave yucca (Yucca schidigera). WeinvestigatedwhetherX.vigilisexhibitshabitatpreferenceforfallenY.schidigeralogmicrohabitatsandwhatfactorsmakecertainlogmicrohabitatsmoresuitableforX.vigilisinhabitation.WefoundthatX.vigilispreferredY.schidigeralogsthatwere larger incircumferenceandshowednopreferencefordeador liveclonalstands of Y. schidigera. When invertebrates were present, X. vigilis wasapproximately50%morelikelytoalsobepresent.TheseresultssuggestthatX.vigilishavepreferences fordifferent typesofY.schidigera logsand logswhereinvertebrates are present. These findings are important as they help inunderstandingoneoftheMojaveDesert’smostabundantreptilespeciesandtheecosystemsoftheMojaveDesertasawhole.
INTRODUCTION
Habitat selection is an importantfactor in the shaping of an ecosystem.Where an animal chooses to live andforagecanaffectdistributionsofplants,predators and prey, and can influenceecosystem processes. Habitat selectionusually occurs at smaller, local scales(Penalver-Alcazaret. al. 2016). This is asignificant concept in harshenvironments with limited resources,
suchastheMojaveDesertinCalifornia.The Mojave Desert has extremetemperature fluctuations, ranging frombelow freezing to over 134.6 degreesFahrenheit (Schoenherr2017). It isalsoextremelydry,with less than10 inchesofrainperyearonaverage(Schoenherr2017). Because of these harsh climaticcharacteristics, species that inhabit thisregion often have specific habitatrequirements and preferences in ordertosurvive(Schoenherr2017).
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Our study investigated the habitatselection and preference of the desertnight lizard (Xantusia vigilis). As asedentary vertebrate, the X. vigilisspendsmost of its life hidden beneathfallen vegetation, rocks, and debris(Marlow 2000). Its prey includestermites, beetles, spiders, ants, andvarious other invertebrates. The X.vigilis is believed to have a stablepopulation and is listed as a species ofleastconcern.Thisspecies’lifehistoryisuniqueinthattheyproducetwotofouroffspring per year with limiteddispersion as they form family groups(Mattern 2016). Some studies havebeen conducted regarding therelationship between X. vigilis and theJoshuatree(Yuccabrevifolia)while lessis known about X. vigilis and itsinteractions with the Mojave yucca (Y.schidigera).The purpose of our study was to
investigateX.vigilis’relationshipwithY.schidigeraandtoexaminepatternsbothin habitat preference and potentialbottom-upmechanisms between thesetwo species. We sought to determinewhetherX.vigilisexhibitedmicrohabitatpreference in different Y. schidigeracharacteristics such as size and clonalstatus. Additionally, we examinedwhether certain Y. schidigeracharacteristics providedmore optimumhabitatforX.vigilis.Lastly,byexaminingthepotentialbottom-upmechanismsinthe relationship between invertebratepresence(asaproxyforfoodresources)and the presence of X. vigilis, weinvestigated why certain Y. schidigeramightbepreferable.Ourstudyprovidesbaseline data that lends to a greater
understanding of X. vigilis distributionandecologyintheMojaveDesert.
METHODS
StudySite
WeconductedourresearchwithintheSweeney Granite Mountains DesertResearchCenterintheMojaveDesertinCalifornia. Siteswerewithina two-mileradius from the research center andwerechosenbasedonhighY.schidigerapresence. Each macro-plot spanned 50m by 100m.We collected data over aspan of four days fromNovember 5–8,2017.
DataCollection
At each site, we sampled everydownedY. schidigera log, avoiding logswith woodrat middens. Samplinginvolvedgentlyflippingandshakinglogsto look for X. vigilis and invertebrates.WecaughtallX.vigilisbyhandandusedforceps tocapture invertebratesbeforepreservingtheminvialscontaining91%ethanol. Each log and X. vigilis wasreturned to its original place oncemeasurementswere taken. For eachX.vigilis,wemeasuredmass(g)andsnout-to-vent (SVL) length (mm). We alsorecorded Y. schidigera circumference(m) and noted whether each sampledstandofY.schidigerawasaliveordead.We identified invertebrates bymorphospecies and calculated theirspecies richness as the number ofmorpho-species found under each Y.schidigeralog.
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StatisticalAnalyses
Allstatisticalanalyseswereperformedusing R 3.4.1. Using logistic regression,we examined the relationship betweenY. schidigera characteristics (clonaldiameter, log height, length,circumference) and presence of X.vigilis.We also used logistic regressiontoexaminetherelationshipbetweenY.schidigera characteristics (clonaldiameter, log height, length,circumference) and presence ofinvertebrates. We used t-tests toinvestigate differences in X. vigilispresence and invertebrate presencebetween dead and live stands of Y.schidigera. Finally, we used a t-test toanalyze the correlation betweeninvertebrateandX.vigilispresence.
RESULTS
Outof108sampledY.schidigeralogs,54% had X. vigilis present. As logcircumferenceincreased,theprobabilityofencounteringX.vigilisunderthat logincreased(n=108,p=0.01;Figure1a).The probability of encounteringinvertebrates also increased as logcircumference increased (n = 108, p =0.01; Figure 1b). There was nosignificant difference in X. vigilispresence between dead and live Y.schidigera stands (n = 108, p = 0.19;Figure 2a). The presence ofinvertebrates under dead Y. schidigeradid not differ from under live Y.schidigera stands (n = 108, p = 0.23;Figure 2b). Lastly, the proportion of Y.schidigerawithX.vigilispresentwas
Figure 1. Probability of Xantusia presence (1a) invertebrate presence (1b) by yuccacircumference. Relationship between Y. schidigera circumference and the probability ofencounteringX.vigilis(1a)andinvertebratepresence(1b)shownbylogisticregression.
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Figure 2. Xantusia and invertebrate presence by yucca status. Relationship between Y. schidigeramortality and the probability of encountering X. vigilis (2a) and other invertebrates (2b) shown byproportionofX.vigilisorinvertebratespresentwithbinomialerrorinrelationtoY.schidigerastatus.
Figure 3. Xantusia presence by invertebratepresence. Relationship between invertebratepresence and X. vigilis presence is shown bytheproportionofX.vigiliswithbinomialerrorin relationtowhere invertebratesarepresentunderlogs.
significantly greater wheninvertebrateswerepresent(n=108,p< 0.01; Figure 3). None of the othertests (regarding diameter, height,length)weresignificant.
DISCUSSION
Overall, we found that X. vigilis seemtoexhibithabitatpreferencebasedonquality level ofY. schidigera, and thatthese habitat associations may bedrivenbygreater resourceavailability.The many variables of Y. schidigerashow that there is heterogeneitywithin X. vigilis habitat structure. WefoundanabundanceofX.vigilis inthemacro-plots, but they only inhabitedhalf of the available logs. A case inSouthernNevadafoundthattherewaspreference of Y. schidigera to Y.brevifoliawhenfoundinthesamearea(Deacon et al. 1966). This studysupportsourspeculationsthatX.vigilisidentify Y. schidigera as an optimalhabitat;eveninareaswithothertypesofyuccapresent,X.vigilisstillpreferY.
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schidigera. After analyzing multiple Y.schidigera variables, we determinedthere were two main logcharacteristics that X. vigilis showedpreferencefor.OurstudyshowedthatX.vigiliswere
more likely to be found under Y.schidigera when invertebrates werepresent. Detritivorous insects, such astermites and ants, prefer to consumethe fiber of decayed plants (Morafka1973).Thesedetritivoresarethemainfood source of X. vigilis (Morafka1973). Favorability of logs containingdetritivorous insects also occurred inPinnacles National Park (Morafka1973). Xantusia vigilis commonlyresided in digger pine that containedtermites, and X. vigilis stomachcontents revealed they were alsoeating ants (Morafka 1973). Both ourstudyandMorafka(1973)indicatethatfood availability is the main drivingforcebehindX.vigilishabitatselection.Our study also showed that X. vigilisprefered larger fallen Y. schidigeralogs. Increased habitat area is anecessity as X. vigilis reside in familygroups foroneto fouryearsata time(Marlow2000).X.vigilisareknowntocongregateduringthewinterseasoninlarge numbers, with up to 14individuals under one log (Marlow2000). Because X. vigilis are reclusiveand socially aggregated, increasedhabitat area and the presence ofinvertebrates in logs is essential toreducecompetition.Finally, our study did not find a
significant difference in X. vigilis’preference for dead or live Y.schidigera stands. Insect presence indead or live Y. schidigera stands also
didnotdiffer significantly. Incontrast,Deacon et. al. (1966) found that thepresence of a live Y. schidigeraprovided shade and assisted inmoistureretainmentintheunderstory.Because of this study, we predictedthismayhave an influenceonhabitatselection in X. vigilis since it will helpkeepthemcoolintheariddesert.Onereason we may not have found acorrelation between the presence oflive Y. schidigera and the presence ofX. vigilis is the existence of animalssuch as desert woodrats (Neotomalepida). X. vigilis have been shown tobe absent from Y. schidigera with N.lepida middens, suggesting predation(Miller 1951). Even without thepresenceofamidden inY. schidigera,theN. lepidamayusetheseplantsforcoverandforaging,deterringX.vigilis.Predatorpresencemaycounteractthepotential benefits of being near a liveY.schidigerastand.Although our study measured and
comparedmultiplevariablesofhabitatpreference, the main factors thatdeterminehabitatpreferencewerenotrecorded. According to Penalver-Alcazar et al. (2016), spatialheterogeneitymodels require data ondifferent sexes and age class of aselected species to truly define aspecies’ ecological requirements.Nevertheless, we were able to definesome characteristics of X. vigilis’preferred habitat that future studiescouldbuildupon.AsX.vigilis ishighlyvulnerable to changes in abiotic andbiotic conditions, it is important tounderstand not only habitatpreference, but spatial heterogeneityto determine future population
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dynamics. Exponential urbanization ofdesert land will transform theecological landscape to thedisadvantage of X. vigilis. Finally,knowledge of X. vigilis habitatpreference and spatial heterogeneitywill allow the future prediction ofresponse to habitat alterations fromclimatechange.
ACKNOWLEDGEMENTS
This work was performed at theUniversity of California’s SweeneyGranite Mountains Desert ResearchCenter,doi:10.21973/N3S942.
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