[1] Uppsala Univ, Dept Ecol & Evolut, S-75236 Uppsala, Sweden
[2] Univ Vienna, Dept Limnol, A-1090 Vienna, Austria
[3] Univ Antwerp, Dept Biol, B-2610 Antwerp, Belgium
[4] Stroud Water Res Ctr, Avondale, PA 19311 USA
[5] Univ Vienna, Dept Chem Ecol & Ecosyst Ecol, A-1090 Vienna, Austria