Natural fluctuations in a stream dwelling newt as a result of extreme rainfall: a 21-year survey of a <em>Calotriton asper</em> population

Abstract

Amphibians living in streams are often subjected to spates. These waterfloods are the main cause of organism drift and mortality, and these effects can be confounded with population decline. Discrimination between population decline and natural fluctuations in unpredictable habitats requires the study of population dynamics through monitoring and long data series. We conducted a 21-year demographic field survey of a newt (Calotriton asper) population in the eastern Pyrenees. Our results indicate that the adult population showed high fluctuations in response to heavy rainfall. Maximal rainfall in 24 h (higher than 50 l / m2) caused population decreases as a result of catastrophic drift. The larval population also decreased after heavy rainfall. The data from this survey show that the population recovered three years after catastrophic drift. Subadult C. asper show terrestrial activity and are not affected by waterfloods. Interannual dynamics revealed that the stock of subadults allowed for rapid population recovery after catastrophic drift episodes. Flooding produced higher mortality when it occurred during winter than during the active cycle of newts. This long-term study provides new insights into the survival strategies displayed
by newts in response to extreme stream environments.