Present address: Instituto de Investigación en Recursos Cinegéticos (IREC), Ronda de Toledo s/n, E-13005 Ciudad Real, Spain.
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Seasonal variation in the contribution of different behavioural mechanisms to lizard thermoregulation
Article first published online: 8 DEC 2004
DOI: 10.1111/j.0269-8463.2004.00916.x
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How to Cite
DÍAZ, J. A. and CABEZAS-DÍAZ, S. (2004), Seasonal variation in the contribution of different behavioural mechanisms to lizard thermoregulation. Functional Ecology, 18: 867–875. doi: 10.1111/j.0269-8463.2004.00916.x
Publication History
- Issue published online: 8 DEC 2004
- Article first published online: 8 DEC 2004
- Received 26 April 2004; revised 11 June 2004; accepted 14 June 2004
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Keywords:
- daily activity;
- operative temperatures;
- patch selection;
- selected range;
- shuttling behaviour
Summary
- 1We studied seasonal changes in the thermoregulatory behaviour of the lacertid lizard Psammodroums algirus in a Mediterranean evergreen forest. Body temperatures (Tb), environmental operative temperatures (Te) and upper and lower limits of the selected thermal range (Tsel) were lower in May than in July.
- 2On average, mean deviations of Tb from Tsel (0·7 °C in both seasons) were much smaller than those of Te (8·3 °C in both seasons). Thus both the accuracy (average difference between Tb and Tsel) and effectiveness (the extent to which Tb are closer than Te to Tsel) of thermoregulation were high, and similar in both seasons.
- 3However the thermoregulatory contribution of two distinct behavioural mechanisms varied markedly between seasons. Daily activity contributed significantly to the regulation of Tb in May (when a population of Te thermometers matching lizard activity patterns would be, on average, 1·0 °C closer to Tsel than were randomly available Te), but not in July (when such a population would be only 0·2 °C closer to Tsel than were randomly available Te). The selection of sun–shade patches, the contribution of which was larger than that of daily activity in both seasons, was more important in July (when it produced a distribution of Te that would be, on average, 3·1 °C closer to Tsel than were randomly distributed Te) than in May (when a population of thermometers matching the lizards’ pattern of exposure to sunlight would be 1·3 °C closer to Tsel than were randomly available Te).
- 4These changes are discussed in the light of seasonal differences in the daily patterns of among-patch variation in Te. In spring, lizard activity was low in the early morning because even the selection of sunlit patches was of limited utility to attain Tb within Tsel; in summer, lizards could remain active at midday, despite low overall thermal suitability, by selecting shaded patches. Thus the contribution of patch selection to thermoregulation was important in the early basking period of both seasons, and at summer midday hours.
- 5Our data suggest that shuttling between sun and shade, rather than selecting sun or shade, may be an additional mechanism of behavioural thermoregulation, the importance of which would be greatest at times of day when lizards use patches at random (e.g. spring midday hours), and that their mean Tb is closer to the grand mean of full sun and full shade Te than to the mean equilibrium Te within any type of patch.