Abstract
Thermoregulatory processes were compared among three-size groups of free-ranging Komodo dragons (Varanus komodoensis) comprising small (5–20 kg), medium (20–40 gm) and large (40–70 kg) lizards. While all size groups maintained a similar preferred body temperature of≈35∘C, they achieved this end point differently. Small dragons appeared to engage in sun shuttling behavior more vigorously than large dragons as represented by their greater frequency of daily ambient temperature and light intensity changes as well as a greater activity and overall exposure to the sun. Large dragons were more sedentary and sun shuttled less. Further, they appear to rely to a greater extent on microhabitat selection and employed mouth gaping evaporative cooling to maintain their preferred operational temperature and prevent overheating. A potential ecological consequence of size-specific thermoregulatory habits for dragons is separation of foraging areas. In part, differences in thermoregulation could contribute to inducing shifts in predatory strategies from active foraging in small dragons to more sedentary sit-and-wait ambush predators in adults.
Highlights
During growth from hatchlings (0.1 kg) to adults, Komodo dragons (Varanus komodoensis) express the entire range of adult body size distribution of the genus Varanus
These examples are typical of other observation days where the number of active small dragons is fairly constant throughout the survey period while the number of medium and large dragons tends to become more bimodal with less activity during midday high-ambient temperature
Komodo dragons that span 4 orders of magnitude in size during ontogenic growth are mobile with large home ranges by reptilian standards that encompass many types of microhabitats [4, 37]
Summary
During growth from hatchlings (0.1 kg) to adults (maximum of 87 kg), Komodo dragons (Varanus komodoensis) express the entire range of adult body size distribution of the genus Varanus. Associated with these changes in body size during growth are shifts in an individual’s ecology including habitat usage, predatory strategies, diet niche, and thermoregulatory behaviors [1,2,3]. We have found this to be true for Komodo dragons which express preferred temperature amplitude of about 35◦C with a duration of around 5 hours regardless of body size [12]. In spite of this similarity in preferred temperature among size groups, the ontogenic transition in body size dictates that thermal/physical properties among lizards will differ, and as such, size-dependent thermoregulatory behavior are predicted to occur to achieve a similar body temperature endpoint
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