Distribution of Brachypelma vagans (Theraphosidae) burrows and their characteristics in Belize over two years

2011·2.6 MB·English

by  Emma M Shaw

2011.TheJournalofArachnology39:515-518
SHORT COMMUNICATION
Distribution ofBmchypebmi vagam (Theraphosidae) burrows and their characteristics in
Belize over two years
Emma M. Shaw, Susan P. Bennettand C. PhilipWheater: Department ofEnvironmental and Geographical Sciences,
Manchester Metropolitan University, Manchester, M15 5GD, UK. E-mail: [email protected]
Abstract. To help to address the paucity ofecological knowledge available for Brachypelnui vagansAusserer 1875, a
CITESprotectedspecies,wemonitoredapopulationinWesternBelizefortwoyearstoprovidedatafordistributionand
dispersal.Despitepreviousover-collectionforthepettrade,thespeciesislocallyhighlyabundantinsomeareasofBelize.
Werecordedthedistribution,burrowandspidercharacteristicsofB. vagansin2007and2008atLasCuevasResearch
Station, Belize. Populationdynamicswerecompared betweenyears,aswasindividual location. Over 100burrowswere
locatedinbothyears;however,previousassumptionsthatindividualsdonotmoveburrowsregularlyappearnegated,since
only12burrowlocationsmatchedbetweenyears,suggestinghighintra-habitatdispersal.Despitethisapparenthighlevelof
movement burrows were significantly clumped, to a similar degree, in both years. This movement could be due to
disturbancesthroughouttheyear,includingHoodingduringtherainyseason.Burrowsizecorrelatedwithindividualbody
size,exceptinafewjuvenilesthatappeartohaveopportunisticallyclaimedanemptyburrow,accountingforsomesmall
animalsfoundinlargeburrows.
Keywords: Burrow,Belize,ecology,red-rumptarantula,populationstructure
Brachypelma vagansAusserer 1875 isoneofthemost ubiquitous currentstudyexaminesthepopulationdynamicsanddistributionof
BrachypelnuispeciesofNeotropicallowlandforesthabitats.Asthese one B. vagans population for two consecutive years to elucidate
tarantulasarelonglived,brightlycoloured,andusuallydocile,they patternsofmovementandactivityandprovidean understandingof
arepopularpetsandsufferfromover-harvesting,nowbeinglistedas thehabitatrequirementsandpopulationpressuresonthespecies.
threatenedCITIESAppendixIIspecies(Petersonetal.2006).Despite Thetechniquesusedoverthetwoyearswereidentical.Thestudy
B. vagans having the widest distribution of Brachypelnui species siteatLasCuevasResearchStation,Chiquibulrainforestarea,Cayo
(being recorded from Mexico, Belize and other parts of Central district,Belize(GPSlocation88°59.188'W, 16°43.990'N,elev.583m)
America:Reichling 1999),thereislimitedinformationonitsecology is classified as lowland tropical broad-leafed rain forest, which
and habitat preferences (e.g., Yanez & Floater 2000; Henaut & stretches from the Caribbean coast ofMexico, through Belize and
Machkour-M’Rabet2005;Machkour-M’Rabetetal.2007;Doretal. into Honduras and the Peten region of Guatemala. The study
2008),withmoststudiesonBrachypelnuitarantulasconcerningtheir populationofB. vagansisintheclearing(150x 121 m)surrounding
geographic distributions (Valerio 1980; Smith 1986; Edwards & research station buildings, which are mainly to the south side (the
Hibbard 1999; Locht et al. 1999), systematics (Coddington & Levi currentresearchconcentratedonthenorthsideoftheclearing:98 X
1991; Perez-Miles et al. 1996) and genetics (Longhorn 2002; 121m).Belttransects(1mwide)werelaidperpendiculartotheback
Longhorn et al. 2007; Machkour-M'Rabet et al. 2009). The rarity oftheclearing(whereitmetforestundergrowth)andsystematically
ofsomeBrachypelmaspecies(e.g.,Yanez&Eloater2000),combined searchedforsignsofburrows,whichwerelabelledusinganumbered
withhabitatdegradationandillegalcaptureandtrade, suggeststhe fiag to enable easy relocation at night, when individuals were
needforcaptivebreedingpriortoreintroduction(Yanezetal. 1999). extracted for measurement. The location of each burrow and its
Itisessentialtherefore,toobtaindetailedknowledgeoftheirhabitat openingdimensions(usingthewidestwidthandlongestlengthofthe
requirements and changes within populations to provide a greater mouth)wererecorded. The surveys took place in June and July in
understandingofthefactorsinfluencingtheirspatialdistributionand both2007and2008.
populationdynamics. Visitingburrowsatnightwhenindividualssatattheburrowmouth
Brachypelmavagansconstructburrowswithsingleentranceswhere gaveaclearindication ofoccupancyand helped to minimizestress
they spend the day, spinning silk around the entrance to transmit when removing animals using a fishing technique (Reichling 2003)
vibrationsfrom preymovements(Yanez& Floater2000). Theyare involvingabladeofgrasswavedtomimicpreymovements.Oncethe
nocturnal predators feeding mainly on ground-dwelling arthropods individualwasremoved,theentrancewasblockedandtheindividual
andpossiblysmallvertebrates(Marshall 1996). Machkour-M’Rabet placedinaclearplasticbagtoallowmanipulationandmeasurement.
etal.(2007)founddensitiesofB. vaganstobehigherinopenrather Whenindividualswerenotseen,theburrowwasmonitoredforsigns
thanforestsitesandwithhighdensitiesofburrowscharacterisedby ofoccupancy(e.g.,silkandsoilextractedfromtheburrow).
deepclayishsoils,whichisunsurprisinggiventhatindividuals,onthe The minimum distance between burrows was calculated using
whole,digtheirownburrows.Littleisknownaboutburrowfidelity trigonometry, and aggregation between burrowswasassessed using
and which factors cause burrow relocation, although some field nearestneighbouranalysis(e.g., Wheateret al. 2011). Theindexof
observations suggest that females locate occupied burrows of aggregation was calculated as the ratio between the mean and the
conspecifics and attack and consume the residents (Henaut & expecteddistancesbetweenburrows(wheretheexpecteddistancewas
Machkour-M’Rabet, 2005). Lack of long-term distributional data estimatedas: l/[2vdensity]). Independentsamples/-testswereusedto
foranyB.vaganspopulationposesdifficultiesindeterminingthelevel examine differences in nearest neighbor distances between years to
ofintra-populationmovement,whetherburrowswappingoccurs,or determinewhetherclusteringdiffers between years (see Krebs 1999
thedistancesthatindividualsmovetofind,ordig,anewburrow.The for a fuller explanation ofnearest neighbor analysis). A Pearson’s
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516 THEJOURNALOFARACHNOLOGY
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Figure 1. Schematicrepresentationofthelocationofallburrowslocatedin2007and2008onthenorthsideoftheLasCuevasResearch
Stationclearing.Theclearingboundaries,pathandbuildingsandfloodzoneareallshownforreference(shadedareas).
product moment correlation coefficient was used to determine burrowstructureasB. vcigaiiscanhaveuptofourchambersoffthe
relationships between spider and burrow size, for all caught main burrow (Machkour-M’Rabet et al. 2007) and be recorded at
individuals,ineachyear. depthsof3-40cm(Machkour-M’Rabetetal.2007)andupto50cm
Over 100burrowswerelocated(108in2007and 107 in2008),of (Shawpers.obs.).Rainfallcanbehighduringthewetseason,andthe
which 80wereoccupied in 2007, and 73 in 2008. More individuals clearingissubjecttoseasonalHooding,which,coupledwiththelack
wereextractedin2007(48comparedto26in2008),andtherewasa of deep roots, could lead to burrow collapse. Of those burrows
higher percentage ofjuveniles in 2007 (41%) than in 2008 (7%). matchingbetween2007and2008somewereprotectedfromcollapse,
Despitethesimilarity in burrow numbersfound in bothyears, it is being underneath the edges of buildings, rocks and large roots.
evidentfromFig. I thattheirdistributionismarkedlydifferentwith Burroworientationcanmakethemmoresusceptibletorain-carrying
aonrloyun1d2bpurielsdeinntgsfraonmdo1nyetahreetodgtehseonfexatc.onMcarnetyebpuatrhr.owAslwaerrgeenluomcabteerd w20i0n5d)s,,hbeultpilnegadtiongmaitontaaintrhaidge-hofhfumbiedtiwteye(nMaocphtkiomuurm-Mh’uRmaibdiettyetanald.
of burrows were found in the west side of the clearing in 2007, having to movewhen flooded. Certainly areas that regularly flood
whereasin2008theproportionpresentinthisareawasreduced.An havealmostnoburrows,andthoseattheedgeofthefloodzonecan
areapronetofloodinghadfewburrowspresentineitheryear(Fig. 1). become waterlogged, resulting in tarantulas sitting huddled at the
Therewasnosignificantdifferencebetweenmeannearestneighbour mouth ofthe burrow until the water subsides. Repeated flooding
distancesbetweenburrowsin2007and2008(f= 1.658,df=213,F= couldresultinabandonment,asobservedinotherburrowingspiders
0m.)0.99B;u2r0r0o7w:smweearne=sig3n.i8f8ic(aSnEtl=yc0l.3u1m)pme;d2i0n08b:otmhea20n07=3(.Z16=(S4.E43=,0d.f27=) j(uMvaernsilheasl,lpo1s9s95i)b.lyAebxapnladionninegdtbheurrloowwscowroruelladtiotnhebnetbweeenfresepidfeorr
107, P< 0.0001)and2008 (Z= 7.23,df= 106, P< 0.0001),with stageandburrowsize.
similarindicesofaggregation(2007:1,4 =0.64;2008:Ia =0.60).For The nearest neighbour analysis showed similar mean distances
occupied burrows, there was no significant difference between the betweenburrowsintheNorthofBelize,asfoundbyReichling(1999:
nearest neighbourdistancesbetweenyears(t = 1.02,df= 152, R = 3.4 m), and those at Las Cuevas (3.88 m, 2007; 3.16 m, 2008),
0.331; Table 1). In both years, occupied burrows were significantly suggesting that there may be an optimal distance driven by
clumped(2007:1,4 =0.77,Z=4.43,df=79,P<0.0001;2008:Ia = competitive repulsion (Reichling 1999). The level ofbetween-year
0.70,Z=5.41,df=72,P<0.0001).However,thespatialdistribution movementimpliedbythisstudymaybeduetorelocationofjuveniles
ofburrowsdifferedbetweenyears(Fig. 1)withthosecontainingadults priorto reachingmaturity. Machkour-M’Rabet et al. (2005)found
being more clustered than those with juveniles, and areas where thatadultsandjuvenilesaggregatedseparately,althoughthisisnot
burrowswerefoundinoneyearbutnotintheother. evident in the study population. Reichling (1999) suggests that
Foreachyear,theoccupiedburrowsizewassignificantlypositively aggregative tendencies in theraphosids could reduce exposure to
correlated with spider body length (2007: r = 0.376, n = 48, F = predatorsandincreasereproductivesuccessofnomadicmalesdueto
0.008; 2008: r = 0.424, n = 26, P = 0.031; Fig.2), and in general theshorterroamingdistancesrequiredbetweenfecundfemales.This
largerspiderswerefoundinlargerburrowswithsomeexceptionsof can further be aided by the presence ofdetectable chemical cues
small juveniles inhabiting what appeared to be abandoned adult (Yanezetal. 1999).
burrows. Dor et al. (2008) found females readily enter burrows ofother
Despitesimilarnumbersofburrowsbeingfoundinbothyears,the females,sometimesresultingintheattackanddeathofoneofthem
locationsweremarkedlydifferent, suggestingthat individualsmove (Henaut and Machkour-M’Rabet 2005). With high densities and
betweenpre-existingburrowsortonewburrows.Examinationofthe clustered burrows, it is possible that there is frequent burrow
clearing in 2008 revealed no visible signs ofold burrows in areas takeover, particularly since chemical cues left by the silk at the
where burrows had previously been present. This could be due to burrowmouthcanattractfemalestoeachother(Doretal.2008).
SHAWETAL.—DISTRIBUTIONOFBRACHYPELMA VAGANSBURROWS 517
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Figure 2. CorrelationbetweenthebodysizeofB. vagcmstarantulasandthewidthoftheirburrowsatLasCuevasResearchStation,Belizein
2007and2008.
Inconclusion,thisstudyhighlightsthatthepopulationofB.vagcmsat Locht, A., M. Yanez& 1. Vasquez. 1999. Distribution and natural
LasCuevasResearchStationisstableandhighlymobile.In2007much history of Mexican species of Brachypelma and Bruchypelmicles
ofthecapturedpopulationwascomposedofjuveniles,whereasin2008 (Theraphosidae,Theraphosinae)withmorphologicalevidencefor
more were adults, suggesting that the population is developing and theirsynonymy.JournalofArachnology27:196-200.
indicatingapotentialpopulationboomasthelargenumberofadults Longhorn, S.J. 2002. Non-lethal DNA sampling from CITES II
producejuveniles.Ifthisisthecase,continuedstudiesonthispopulation protected‘tarantula’spidersofBelize.LasCuevasNewsletter9:8-9.
shouldhelpelucidatesomepatternsofdispersalanddistribution. Longhorn, S.J., M. Nicholas, J. Chuter & A.P. Volger. 2007. The
ACKNOWLEDGMENTS utilityofmolecularmarkersfromnon-lethalDNAsamplesofthe
CITES II protected “tarantula” Bracypelma vagans (Araneae,
TheauthorswouldliketothankallthestudentsontheManchester Theraphosidae).JournalofArachnology35:278-292.
Metropolitan University and the University of Manchester Belize Machkour-M’Rabet.S.,Y.Hennaut,R.Roberto&S.Calme.2005.Anot
fieldcourse, VickyOgilvy, whoassistedwith collectingindividuals, so natural history ofthetarantula Brachypelma vagan.s\ Interaction
andLasCuevasResearchStationandtheBelizeForestryDepartment withhumanactivity.JournalofNaturalHistory39:2515-2523.
forallowingthisworktobeconducted. Machkour-M’Rabet, S., Y. Hennaut, A. Sepulveda, R. Rojo, S.
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