Brian W. Weavers’s scientific contributions

Varanus mertensi is a semiaquatic lizard that lives near permanent water in northern Australia. During the wet and dry seasons, we measured the field metabolic rate (FMR) and water flux rates of animals in the field and standard metabolic rates across a range of body temperatures (18-96 C) in the laboratory. We combined these data to divide the FMR into energy expended during periods of rest and activity. The FMR was significantly higher in the wet season (120.7 kJ kg(-1) day(-1)) than in the dry season (81.1 kJ kg(-1) day(-1)). There was no difference in the water flux rate between the wet (63.2 ml kg(-1) day(-1)) and dry (66.5 ml kg(-1) day(-1)) seasons. The FMR during the wet season is greater than that predicted for a similarly sized iguanid lizard, but the 95% confidence interval around the mean FMR in the dry season overlaps the predicted iguanid value. The calculated percent of the FMR devoted to activity is high for both seasons (70-73%) compared to other lizards, as is the calculated sustainab

The aims of this paper are to compare the thermal ecology of four species of varanid lizards that occupy a range of habitats and climatic regions, and to assess the efficacy of methods for evaluating the extent to which ectothermic animals exploit their thermal environments. Hertz et al. (1993) have proposed several indices of thermoregulation, and these are evaluated with respect to our data from varanid lizards. The thermoregulatory characteristics of three tropical monitor lizards (Varanus panoptes, V. gouldii, and the semiaquatic V. mertensi), and the temperate-zone V. rosenbergi were studied throughout the year. Radiotelemetry was used to measure the body temperatures (Tb's) of free-ranging animals, and microclimatic data were collected to determine the range of possible Tb's that an animal could achieve. Operative temperatures (Tb's) were estimated by biophysical models for each set of animal characteristics and microclimatic conditions. The Tb's selected by animals in a laboratory thermal gradient were used to determine the set-point range of Tb's that the animals voluntarily select. Plots that superimpose Tb's, Te's, and the set-point range across the day are extremely useful for describing the thermoregulatory characteristics of ectotherms. These plots can be used to determine the extent to which the animals exploit their thermal environment: we define an index of thermal exploitation (Ex) as the time in which Tb's are within the set-point range, divided by the time available for the animal to have its Tb's within the set-point range. Only V. mertensi was active throughout the year. In general, during seasons of inactivity, the Tb's of inactive species fell outside the set-point range, but during periods of activity all species selected Tb's within their set-point range. The temperate-zone species (V. rosenbergi) thermoregulates very carefully during periods when environmental conditions allow the animals to attain the set-point range, and V. gouldii also thermoregulates carefully in the wet season. V. mertensi selects Tb's that are significantly lower than the other species both in the field and in the laboratory, and thermoregulatory indices of this species were intermediate relative to the other species. The amount of time spent in locomotion each day was not correlated with the indices of thermoregulation: the most active species, V. panoptes, was, with respect to several indices, the least careful thermoregulator. The type of question that is being addressed, with respect to the interactions between an animal's thermal environment and its thermoregulatory behavior, determines the appropriateness of the various indices of thermoregulation. The Ex index describes the thermoregulatory characteristics of ecotherms in a heterogeneous thermal environment, and in such an environment a large amount of information can easily be interpreted graphically. This index is less useful in a thermally homogeneous environment.

The field metabolic rates (FMR) and rates of water flux were measured in two species of varanid lizards over five periods of the year in tropical Australia. The energetics of these species were further investigated by directly measuring activity (locomotion) and body temperatures of free-ranging animals by radiotelemetry, and by measuring standard metabolic rate (over a range of body temperatures) and activity metabolism in the laboratory. Seasonal differences in the activity and energetics were found in these goannas despite similar, high daytime temperatures throughout the year in tropical Australia. Periods of inactivity were associated with the dry times of the year, but the onset of this period of inactivity differed with respect to habitat even within the same species. Varanus gouldii, which inhabit woodlands only, were inactive during the dry and late dry seasons. V. panoptes that live in the woodland had a similar seasonal pattern of activity, but V. panoptes living near the floodplain of the South Alligator River had their highest levels of activity during the dry season when they walked long distances to forage at the receding edge of the floodplain. However, during the late dry season, after the floodplain had dried completely, they too became inactive. For V. gouldii, the rates of energy expenditure were 196 kJ kg–1 day–1 for active animals and 66 kJ kg–1 day–1 for inactive animals. The rates of water influx for these groups were respectively 50.7 and 19.5 ml kg–1 day–1. For V. panoptes, the rates of energy expenditure were 143 kJ kg–1 day–1 for active animals and 56 kJ kg–1 day–1 for inactive animals. The rates of water influx for these two groups were respectively 41.4 and 21.0 ml kg–1 day–1. We divided the daily energy expenditure into the proportion of energy that lizards used when in burrows, out of burrows but inactive, and in locomotion for the two species during the different seasons. The time spent in locomotion by V. panoptes during the dry season is extremely high for a reptile (mean of 3.5 h/day spent walking), and these results provide an ecological correlate to the high aerobic capacity found in laboratory measurements of some species of varanids.