Snails keep the pace : shift in upper elevational limit on mountain slopes as a response to climate warming

Predicted biological responses to climate warming are changes in phenology and poleward shifts or upslope displacements of the distribution of species. We investigated changes in the upper elevational limit of the land snail Arianta arbustorum (L., 1758) by repeating historical records from 1916 to 1917 on nine mountain slopes in the Swiss National Park in 2011-2012. We found that the upper elevational limit for snail populations has risen, on average, by 164 m in 95 years, accompanying a 1.6 degrees C rise in mean annual temperature in the investigation area. The higher temperature results in an upslope shift of the vegetation and in a prolonged activity period of the snails. Upslope extension of snail distribution was not influenced by the inclination of the slope, but it was larger on south-exposed slopes (mean: 233 m) than on north to northeast exposed slopes (122 m). On some slopes we found that the snails have already reached natural barriers (vertical rock walls with no soil), preventing any farther upward dispersal. To our knowledge, this is the first evidence for an invertebrate species with low dispersal capacity ascending to higher elevations in a mountain area in response to climate warming.