Age structure in a declining population of Rana temporaria from northern Italy

In recent years the population of Rana temporaria from Laghi Paradiso (northern Italy) declined without any appearing reason. We applied skeletochronology to study the age structure of this population during the breeding season 2005. Males were on average smaller in body length than females. The modal age was 6 yrs in males and 3 yrs in females. Maximum age ascertained (10 yrs) was the same in both sexes. Sexual maturity was attained after the second or third year from metamorphosis in males and after the third year in females. Based on skeletochronological patterns, we conclude that in the examined population of R. temporaria females are larger than males not because they are on average older but because they grow faster beginning their pre-adult stages of life (2 yrs), this fact contributing to sexual size dimorphism in adults. Comparisons with skeletochronological data obtained from other European populations of R. temporaria confirm that in this species body length, longevity and age at maturity are inversely correlated to the activity period. Finally, we aimed to investigate potential demographic factors responsible for decrease in the study population.