No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Current paradigms relating to reptilian temperature regulation are derived almost entirely from data on diurnally active species, although many reptile species are nocturnal. We investigated the extent and behavioral mechanisms of temperature regulation in the nocturnal, rock-dwelling marbled gecko Christinus marmoratus during spring and summer. During the daytime, we recorded body temperatures of lizards sheltering beneath rocks, as well as operative temperatures (the equilibrium body temperatures that animals would attain in given microclimates) beneath randomly chosen rocks available to the lizards. These measurements were compared with reference to the lizard's set-point (or target) temperature range (Tset), which we determined in a laboratory thermal gradient. In both seasons, lizard body temperatures were closer to Tet than were randomly sampled operative temperatures, despite mean operative temperatures being 70C below and 60C above T, in spring and summer, respectively. The mean body temperature of geckos was 70C higher, and the accuracy and effectiveness of temperature regulation were also much higher, during summer than during spring. The more severe physiological consequences of thermoconformity during summer, as well as a more constraining thermal environment during spring, are advanced as reasons for this seasonal pattern.At least two behavioral mechanisms allow C. marmoratus to achieve a regulated body temperature. First, operative temperatures within retreat sites selected by geckos were closer to T5, than were operative temperatures beneath available rocks, suggesting retreat-site selection as a thermoregulatory mechanism. Second, lizard body temperatures were closer to Tset than were operative temperatures at random positions within selected retreat sites. This observation, together with correlative evidence relating lizard body temperature to the maximum and minimum operative temperatures beneath selected retreat sites, indicates that positional and/or postural adjustments were also employed as thermoregulatory mechanisms. This study suggests that nocturnal lizards are capable of regulating body temperature to an extent that is comparable to that of diurnal lizards. Our findings have implications for understanding the thermal physiology and ecology of nocturnal ectotherms.

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Populations of Pseudomys hermannsburgensis and Notomys alexis were studied during a 33-month period (January 1991 to September 1993) in a sand-dune habitat in south-western Queensland. Population numbers of both species fluctuated dramatically over time with an approximately 40-fold difference between periods of lowest and highest abundance. Increased numbers were due primarily to an influx of juveniles to the population. A high turnover of individuals in both populations resulted in low rates of recapture. Numbers of both species were correlated positively with an index of rainfall with a time-lag of four months. P. hermannsburgensis showed spatial and temporal correlations with seed availability, whereas N. alexis displayed a strong, but non-significant, temporal trend with seed availability. These data suggest strongly that natural irruptions of Australian desert rodents are triggered by rainfall and possibly rain-induced food availability.

A population of Rattus villosissimus was studied during an 18-month period in a sand-dune habitat in south-western Queensland. The population numbers fluctuated dramatically during this time. Increases in population numbers were due primarily to immigration, with reproduction playing a secondary role. Rain-induced increases in food availability are the most likely stimuli for these increases. The cause of population decline is not clear from this study, but predation and disease may be important factors. Radio-tracking showed that the spatial activity of the animals was concentrated on the sides of the dunes, and around burrows. Temporal activity is influenced by moonlight, with animals remaining in burrows for long periods of time on bright nights.