Epsilon Archive for Student Projects

Abstract

The impact of climate change on reptile populations is poorly studied, and this includes snakes, which are elusive by nature, making it problematic to preform long-term population studies. Here we have done both. With the help of over 60 years of mark-recapture data, 1942-2009 and 2021-2022, on a population of grass snakes (Natrix natrix), the goal was to assess the implications of climate change on the population dynamics.
The results found that adult survival was higher during the winter compared to the summer, especially for smaller individuals. Winter survival was positively influenced by increased winter precipitation, which is probably correlated with a greater snow cover. However, winter survival has decreased over time in line with climate change. The opposite was observed in summer survival, which has increased over time. Summer survival increased with the size of the snake, and along with this increasing winter and summer temperatures, associated with longer active periods, seem to have increased the body size of the snakes, especially the males. Males and females have increased in size with 5 and 9 cm, respectively, over a 60 years period.
Survival was also higher in males compared to a same sized female. Probably as a result of different predation pressure and/or higher survival cost of reproduction for the females. We also observed a decrease of the male ratio in the population over the years.
In line with a changed climate, the influence of season on survival, changes with increasing survival during the summers, and the opposite during the winter. But since the population seem to have been stable over time, the negative effects of increased winter mortality could have been balanced by the increased summer survival. As for now, there are no visible complications on the snake population due to climate change. But since the winters are expected to become more unstable which results in more extreme weathers, and as the survival is affected by factors associated with these changes, N. natrix could be threatened in a nearby future.