Ortega, Z. & V. Pérez-Mellado

The effect of thermal requirements on microhabitat selection and activity of Podarcis lilfordi (Squamata: Lacertidae). pp. 351-358.

Abstract. Selection of thermally suitable microhabitats plays an important role in the thermoregulation of ectotherms. We studied microhabitat preferences in two populations of the Balearic lizard, Podarcis lilfordi, that live on two coastal islets of Menorca (Balearic Islands, Spain: Aire and Colom). To assess the roles of different microclimatic traits driving lizards’ decisions, we employed a case/control design. We measured microclimate variables in locations used by lizards (cases) and in paired random unused locations (controls). By comparing paired cases vs controls, we prevent spatial and temporal variation of environmental conditions. In order to test if microhabitat selection depends on thermoregulation requirements, we studied lizards in three situations: (1) ‘cold’, when body temperatures (Tb) of lizards were below their preferred temperature range (PTR), (2) ‘optimal’, when Tb were within the PTR, and (3) ‘warm’, when Tb exceeded the PTR. Substrate temperature was the main abiotic trait that determined microhabitat preferences of P. lilfordi, sometimes in conjunction with air temperature, while wind speed and humidity were not significant. ‘Cold’ lizards selected warmer microhabitats than the mean, but only on Colom islet. Notably, ‘optimal’ lizards also preferred microhabitats that were warmer than their surroundings, and ‘warm’ lizards did not select cold microhabitats in order to cool themselves, but rather acted randomly regarding temperature, wind and humidity. These results for ‘optimal’ and ‘warm’ lizards were consistent for both islets. We also studied the beginning and end of lizards’ diel activity. We found that lizards on Aire were active for approximately one hour more per day than lizards on Colom, which might be related to differences in melanism. However, activity started at an air temperature of approximately 17–19°C and finished at approximately the same temperature on both islets.
Key words. Balearic lizard, behavioural thermoregulation, habitat choice, islands, Lacertidae, Menorca, microclimate, temperature, wind speed.