ECOLOGICAL ENERGETICS AND FOOD ACQUISITION IN DENSE MENORCAN ISLET POPULATIONS OF THE LIZARD PODARCIS-LILFORDI

1. Ecological energetics and water fluxes were compared between popula tions of the lacertid lizard Podarcis lilfordi from the Menorcan islet s of Aire and Nitge (Balearic Islands, Spain) during a non-reproductiv e summer period using the doubly labelled water technique. 2. Lizards from Aire were larger than those from Nitge (9-6 +/- 0.58 g vs 5.1 +/- 0-38 g, respectively) and consequently had higher field metabolic rat es (FMR) (1.739 +/- 0.151 kJ day-1 vs 1.255 +/- 0-977 kJ day-1). 3. FM R were lower in the Aire population, when the effects of the differing body masses were removed. 4. There were substantial differences in fo od availabilities between the two islets and this was reflected in str ong dietary differences between the lizard populations. 5. Feeding con straints were potentially lower in Aire owing to (a) greater arthropod availability, (b) greater abundance of edible flowers, and (c) lower lizard density. 6. We suggest that a reduction in constraints on food intake could enable more efficient foraging by Aire lizards, and so ex plain their lower mass-independent FMR. 7. Although omnivory in Aire l izards appeared to increase the amount of preformed water obtained fro m the food, no differences in mass-independent water flux were found, probably because drinking represented the primary source of water inta ke.