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Identifier

000342024

Title

Στοιχεία οικολογίας και θερμικής βιολογίας της σαύρας Podarcis Cretensis

Alternative Title

Elements of ecology and thermal biology of the lizard Podarcis Cretensis

Author

Σπανέλη, Βασιλική

Thesis advisor

Μυλωνάς, Μωησής

Abstract

The central aim of the present study was to collect data on the ecology of the recently described lizard species Podarcis cretensis (Squamata: Lacertidae), endemic to Crete and satellite islands. For this purpose we studied 5 populations of the species during two seasons: spring and summer 2007. We focused on the approach of the thermal ecology of the species, as well as the effects of the season, the habitat type and the altitude on the thermoregulatory strategies the populations adopt. Simultaneously, we estimated the density of the 5 populations, their activity patterns, the predation pressure they suffer and the percentage of the animals that were infected with ectoparasites. 377 lizards were captured for the needs of this study. We used the line transect method to estimate population densities. Activity patterns were derived from the time of captures during each sampling season. We used the percentage of examined animals with cut or regenerated tails as an index of predation pressure along with a predation simulation experiment. Results showed that male lizards of the species were captured more frequently than females and were mostly infected with ectoparasites, regardless of the season. Activity patterns seem to be rather single-peaked during spring but double-peaked during summer. Population densities of the study species and predation pressure did not vary significantly among the 5 examined biotopes. To investigate the thermal ecology of P. cretensis, we collected field body temperatures of active lizards, along with the available operative temperatures and we used a laboratory thermal gradient to estimate each population’s selected temperature range. Based on these data, we calculated indexes of precision, accuracy and effectiveness of thermoregulation, along with the index of the habitat’s thermal quality, which we used to evaluate the thermoregulatory strategies that the 5 study populations adopt during the two sampling seasons. According to the results, the thermal preferences of the 5 study populations did not vary significantly. All populations proved to be active thermoregulators and achieved higher accuracy and effectiveness of thermoregulation during summer. It also seems that P. cretensis adjusts its thermoregulatory strategy according to the conditions prevailing. In habitats where thermal restrictions are increased (e.g. high altitude sites), it thermoregulates effectively in spite of the associated costs, while in mild environmental conditions and if other ecological restrictions (e.g. risk of predation) are increased, it adopts a rather conservative thermoregulatory strategy. In all cases, it seems that the type of habitat -and in particular the percentage of surface coverage- has an impact on the species’ thermoregulatory strategy: in habitats with high percentage of surface coverage (i.e. plants & rocks), where it takes advantage of the thermal heterogeneity and the safety against predators, it achieves higher accuracy and effectiveness of thermoregulation than in habitats of similar or higher thermal quality, but with lower percentage of surface coverage.

Physical description

128 σ. : εικ. ; 30 εκ.

Language

Greek

Subject

Lacertidae

population density

predation

thermoregulation

ενδιαίτημα

θήρευση

θερμική βιολογία