Species immigration, extinction and turnover of vascular plants in boreal lakes

Dictated by limited resource availability for land acquisition, a central q uestion in conservation biology is the ability of areas of different size t o maintain species diversity. The selected reserves should not only be spec ies rich at the moment, but should also maintain species diversity in the l ong run. We used two sets of data on vascular plant species in boreal lakes collected in 1933/34 and 1996 to test the relationships between lake area and the extinction, immigration and turnover rates of the species. Moreover , we investigated, whether the number of species in 1933/34 or water connec tion between lakes was related to extinction, immigration and turnover rate s of species. We found that lake area or shoreline length was not correlate d with immigration or turnover rate. But extinction rate was slightly negat ively correlated with shoreline length. The original number of species was positively related to the number of species extinctions and to the absolute turnover rate in the lakes, which indicates that species richness does not create stability in those communities. Species number was not correlated w ith immigration rate. Upstream water connections in the lakes did not affec t immigration, extinction or turnover rates. We conclude that length of the shoreline is a better measure of suitable area for water plants than the l ake area, and that because the correlation between shoreline length and ext inction rate was slight. also small lakes can be valuable for conservation.