SOME ASPECTS OF POPULATION BIOLOGY IN THE EUROPEAN TREEFROG, HYLA ARBOREA

Abstract

We studied a population of European treefrogs (Hyla arborea) during the breeding seasons in 1990 and 1991. All treefrogs were individually marked and their ages were determined by skeletochronology. Adult year-to-year survivorship was 37% and 20% for males and females, respectively, but this difference was not statistically significant. There were also no significant dif- ferences in age-specific survival rates. Males outnumbered females at the breeding site in both years; the observed sex ratio was 1.52:1 and 2.15:1 in 1990 and 1991, respectively. In general, males and females reached maturity at 2 yr, and the oldest individuals found were 6 yr in both sexes. Body size and age were positively correlated in both males and females. However, there was a decrease in growth rate with increasing body size and age in both sexes, resulting in considerable overlap of body size among different age classes, especially for older frogs. The age structure of the breeding population differed considerably between the two study years. This difference in the age structure was correlated with yearly differences in the amount of rainfall during the reproductive season, which mainly affects larval survivorship and, thus, adult recruitment.