Grouping behaviour in the armadillo girdled lizard, Cordylus cataphractus

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

[发布机构] Stellenbosch University