XVI International Botanical Congess

Distribution of aquatic plants was studied in 50 lakes during 50 years period. Some species were found in the same few lakes in all censuses with no extinctions or colonisations and obviously have distinct, closed populations. Many species have wide distributions in majority of the lakes forming open populations. Some of the species occur only in a fraction of the ecologically available lakes and show high numbers of extinctions and colonisations. Lake area and isolation affect significantly population dynamics of these species. Unoccupied lakes and those where populations became extinct were also smaller and more isolated than those with persistent populations. Species with this kind of dynamics are evidently distributed in metapopulations.