Decreases over time in shannon diversity of land snails

Sammanfattning: With rising temperatures as a consequence of climate change, suitable habitats for land snails in the northern hemisphere may be shifting northwards. However, there is a lack of studies that explore the latitudinal effects that climate change has on land snails. Therefore, the aim was to see if there are any temporal changes in the species composition of land snails. This was done using sieve samples with land snails that had been repeatedly collected from two sites in southern Sweden. Latitudinal data was provided by two different databases regarding the northernmost and southernmost range limits of the species that were found at the sites. The latitudinal preference of the species composition at the sites was calculated using the latitudinal data. Simple linear regression was used to assess whether the Shannon diversity for the samples was predicted by precipitation, temperature, or year. Simple linear regression was also used to test whether the latitudinal preference of the species composition was predicted by year. It was shown that the Shannon diversity was significantly negatively correlated with year for both of the sites. However, no significant effects of the other predictor variables on the Shannon diversity were found. These results suggest that something is going on which is causing the Shannon diversity to decrease. Also, the results do not exclude that there could be a real effect of latitude, as the latitudinal data may not be sensitive enough to detect a change in latitudinal preference over time for the species composition. Therefore, in future studies, it would be relevant to put some extra effort into examining what is causing the decrease in Shannon diversity over time.