Reproductive site selection and characteristics of sources and sinks in an Italian Tree Frog metapopulation (Hyla intermedia, Boulenger 1882)

Abstract

In this work we carried out one of the first extensive field researches on the reproductive site selection and the reproductive success of a wide metapopulation of Italian Tree Lrog (Hyla intermedia), an Italian endemism that only recently has been recognized as different from the better known European Tree Erog (Hyla arborea). An accurate census of all the water sites in the territory of the “Baraggia del Piano Rosa” Natural Reserve (Piedmont, Northern Italy) was conducted in the years 1997 and 1998. This particular environment (anthropogenic sub-montane continental heathland) is characterized by a heterogeneous open landscape and many small seasonal wet zones. We observed a good overall presence of tree frogs and their spatial distribution showed a typical metapopulation structure. Data collected on many environmental parameters characterizing the sites and their surroundings were investigated using Discriminant Function Analysis, in function of the presence and reproductive use by H. intermedia and their role in a “source-sink” metapopulation model. These analyses show that tree frogs avoided almost completely deep, shadowed, permanent water sites, suggesting the strong thermophily of the species. Generic disturbance caused by human activities resulted to influence negatively H. intermedia reproduction, but not their presence. The preference for intermediate and advanced phases in the hydroserai succession was also evidenced. Our study indicated the importance of some “source” sites characterized by a trade-off between water temperature and stability for the successful completion of the critical larval stage.