The increase of an amphibian population: 11 years of Rana temporaria Egg-mass monitoring in 30 mountain ponds

Mount Guglielmo in the Italian Alps is an ancient transhumance area where man-made ponds for watering cattle are an ancestral component of the landscape and represent the most important breeding sites for common frogs (Rana temporaria) in the study area. Egg-masses in 30 mountain ponds from the Mount Guglielmo were counted from 2005-2015 to monitor the population trends of R. temporaria, after a putative population decline due to lethal bacterial infections which affected the tadpoles from 2002 to 2006. Egg-mass counts were also used to understand how the recovery of ponds from the natural process of drying-out and the replacement of traditional ponds with pools waterproofed with polymers influence the population dynamics of R. temporaria and the suitability of the ponds as breeding sites. This R. temporaria population increased over the study period, suggesting that the population was able to withstand long lasting larval mortality. Population increase was also sustained by the recovery of some dried ponds, but the modern pools were less suitable than traditional ponds for R. temporaria reproduction. These results suggest that the persistence of the traditional practices related to transhumance (e.g. maintenance of man-made ponds) in the study area is probably of pivotal importance for the conservation of the local herpetofauna.