Structure of a population of the lizard Podarcis bocagei in northwest Spain:: variations in age distribution, size distribution and sex ratio

Mark-recapture techniques were used to investigate population size, age distribution, size distribution and sex ratio in a population of the lacertid lizard Podarcis bocagei in an abandoned gravel pit in northwest Spain. The study was carried out over a 2-year period. Despite relatively high maximum longevity, the population age distribution was characteristic of small, short-lived lizard species (i.e., there was a relatively high proportion of immature individuals). Population size declined over the study period, largely because of a drop in the number of immature animals: this may be partially attributable to density-dependent factors, but was probably due largely to a decline in habitat favourability as a result of colonisation of the study site by vegetation. The sex ratio was significantly female-biased in all cohorts studied, not only among adults but also among juveniles and sub-adults. However, sex ratio at hatching (as investigated by laboratory hatching of clutches laid by captured pregnant females) did not differ significantly from one-to-one. There was no difference found in survival probabilities between males and females. The observed bias in sex ratio must therefore be attributed to between-sex differences in net emigration.