ACKNOWLEDGMENTS
We are grateful to J. Ejsmont-Karabin, J. Uchmanski,
and I. Sawicka for constant assistance
and providing the opportunity to perform studies
at the Hydrobiological Station belonging to
the Center for Ecological Research of the Polish
Academy of Sciences inMikolajki. This work
was supported by the Polish Ministry of Sciences
and Higher Education and the Russian and Belorussian
Foundation for Basic Research.