Grouping behaviour in the armadillo girdled lizard, Cordylus cataphractus

Visagie, Louise (2001-12)

Thesis (MSc)--University of Stellenbosch, 2001.

Thesis

ENGLISH ABSTRACT: Cordy/ us cataphractus and C macropholis naturally occur in groups on a year round basis. I examined whether limited shelter availability might be responsible for this phenomenon. Individuals were provided with an excess of shelter sites and the observed pattern of shelter occupation was contrasted to that obtained for the solitary living species C polyzonus. Cordy/us cataphractus consistently occupied fewer shelters than its two congeners. Results suggest that grouping behaviour in this species is not the result of a limitation in refuge sites. In contrast, the pattern of shelter occupation by C macropholis did not differ significantly from that of C polyzonus, thus the aggregative behaviour observed in the former species may partially be attributed to limited shelter availability in its natural habitat. Conspecific recognition by means of pheromonal detection has been reported in many lizard families, but only for one member of Cordylidae, namely Cordy/us cordy/us. Cordylus cataphractus individuals were exposed to ceramic tiles that had been labeled by conspecific male and female substrate deposits. Labeling was achieved by using ceramic tiles as the bottom half of a shelter in a lizard's home cage for ten consecutive days. Washed tiles were used as controls. Labeled tiles did not elicit significantly more tongue-flicks than control tiles from test specimens in a series of trials. The apparent lack of conspecific recognition via pheromonal detection might be attributable to the group-living nature of this species, which primarily use visual cues for identification purposes. Tongue-flicking is generally utilized in C cataphractus in the detection of novel stimuli. Spatial dynamics of the group-living cordylid, C cataphractus, were investigated by studying patterns of intergroup movement. To date, literature has assumed that C cataphractus groups represent family units, implying low or delayed dispersal rates and high group fidelity. A mark-recapture experiment on six groups included three recaptures outside of and three recaptures within the mating season. High percentages of male, female and juvenile lizards left their groups, but might be an artifact of microhabitat disturbance. High proportions of males, females and juveniles entering the groups, both outside of mld within the mating season, clearly implied a high rate of intergroup movement. Activity and foraging patterns were studied in group-living C. cataphractus lizards by conducting direct field observations between September 1998 and October 1999. The influence of general weather patterns as well as the effect of group size on these patterns were investigated by observing a small-sized, medium-sized and large group. Each group was observed for a minimum of three sunny days per season, with scans conducted every 30 minutes between the hours of 08:00 and 20:00. There was a high rate of activity during the mating season in spring (September). Activity declined sharply mld foraging ceased at the onset of warm, dry conditions (February). Virtually no activity occurred just prior to the first winter rains (July), after which the lizards emerged to forage and replenish energy stores before onset of the next mating season. Selective inactivity might be employed to reduce energy expenditure in this group-living lizard, where intraspecific competition is stringent. Groups of different sizes display different thresholds at which it becomes energetically viable for group members to emerge, as well as different patterns of spatial use around their respective home crevices. Members of larger groups perched further from their crevices, ran further to catch prey mld had less potential prey capture events per individual. Lizards in the larger groups also displayed sporadic lengthy foraging excursions. Such movements might explain the evolution of tail-biting behaviour and heavy armour, which are defensive strategies associated with open areas.

AFRIKAANSE OPSOMMING: Cordylus cataphractus en C. macropholis word dwarsdeur die jaar in groepe in hul natuurlike habitat aangetref. Daar is nagevors of 'n beperking in aantal beskikbare skuilplekke vir hierdie verskynsel verantwoordelik is. Individue is van 'n oormaat skuilings voorsien en die waargenome patroon van skuilplekbesetting is gekontrasteer met dié verkry vir '11 enkelwonende species, naamlik C. polyzonus. Cordylus cataphractus het voortdurend minder skuilplekke beset as sy kongeneriese species. Groepsgedrag in C. cataphractus is dus nie die resultaat van 'n tekort aan beskikbare skuilplekke nie. In teenstelling hiermee het die patroon van skuilplekbesetting vertoon deur C. macropholis nie noemenswaardig verskil van dié van C polyzonus nie. Dus mag die groepsgedrag wat gewoonlik in C. macropholis waargeneem word 'n uitvloeisel wees van 'n beperking op die beskikbaarheid van skuilplekke in sy natuurlike habitat. Herkenning van speciesgenote deur waarneming van ferornone is vir verskeie akkedisfamilies gerapporteer, maar slegs vir een lid van Cordylidae, naamlik C. cordylus. Cordylus cataphractus individue is blootgestel aan keramiekteëls wat gemerk is met substraat-neerleggings van manlike en vroulike speciesgenote. Sodanige merking is uitgevoer deur die keramiekteëls vir tien dae lank te gebruik as die onderste helfte van akkedisse se skuilplekke in hul tuishokke. Gewaste teëls is as kontroles gebruile Gemerkte teëls het nie statisties beduidend meer tongskiete van die akkedisse uitgelok as kontrole teëls in 'n reeks toetse nie. Die klaarblyklike afwesigheid van speciesgenootherkenning deur middel van feromoon waameming kan moontlik toegeskryf word aan die groeplewende gedrag van C. cataphractus, wat primêr visuele informasie vir identifikasie gebruik. Cordylus cataphractus gebruik tongskiete oor die algemeen vir die waarneming vannuwe omgewingsstimuli. Die ruimtelike dinamika van 'n groeplewende gordelakkedis, C. cataphractus, is ondersoek deur die patroon van intergroepbeweging na te vors en groepsgetrouheid te meet. Tot op datum is daar in die literatuur aanvaar dat C cataphractus groepe familie-eenhede verteenwoordig, wat lae of vertraagde verpreidingstempo' sasook' n hoë mate van groepsgetrouheid impliseer. 'n Merk-hervang eksperiment is op ses groepe uitgevoer, insluitend drie hervang episodes buite en drie binne die paarseisoen. 'n Hoë persentasie manlike, vroulike en onvolwasse akkedisse het hul groepe verlaat, maar dit mag bloot 'n uitvloeisel van versteuring van die mikrohabitat wees. 'n Hoë proporsie mannetjies, wyfies en onvolwassenes het egter by die groepe aangesluit, beide buite en binne die paarseisoen, wat onteenseglik op 'n hoë mate van intergroep beweging dui. Daar kom derhalwe veel vryer bewegingspatrone in hierdie species voor as voorheen vermoed en dit is hoogs onwaarskynlik dat groepe familie-eenhede verteenwoordig. Aktiwiteits- en voedingspatrone van die groeplewende akkedis, C cataphractus, is bestudeer in 'n reeks veldobservasies tussen September 1998 en Oktober 1999. Afgesien van die invloed van algemene weerspatrone. is die effek van groepgrootte op hierdie patrone ondersoek deur 'n klein, medium en groot groep te observeer. Elke groep is waargeneem oor . 'n minimum periode van drie dae per seisoen met opnames elke 30 minute, tussen 08:00 ten 20:00. 'n Hoë aktiwiteitsvlak is gedurende lente tydens die paarseisoen gehandhaaf (September). Met die aanvang van warm en droë kondisies (Februarie) het aktiwiteitsvlakke skerp begin daal en voedingsgedrag is gestaak. Feitlik geen aktiwiteit was waarneembaar kort voor die eerste winterreëns (Julie) nie, waamá akkedisse intensiefbegin voed het om energiestore op te bou voor die aanvang van paartyd. Selektiewe onaktiwiteit verminder moontlik energieverbruik in hierdie groeplewende akkedis, waar intraspesifieke kompetisie streng is. Verskillende groepgroottes beskik oor verskillende perke waar dit vir die individu energeties voordelig sou wees om uit die skeur te kom, asook 'n variasie in ruimtelike gebruik om die skeur. Individue van die twee groter groepe het nader aan hul rotsskeur gesit, het verder van die skeur af prooi vang en het beduidend minder potensiële voedingskanse gehad. Akkedisse in die groter groepe het voorts sporadiese lang voedingsekskursies getoon. Hierdie bewegings mag die evolusie van stertbytgedrag en 'n swaar pantser, verdedigingstrategieë wat met oop areas geassosieer word, verduidelik.

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