Résumé
Much research has been devoted to the ecological interactions in food webs in the littoral. Different kinds of grazers such as snails play a very important role in this ecological system. I investigated the snail-periphyton interactions in 3 laboratory experiments. In the first experiment, I tested whether different snails select their food based its quality. The results showed that Valvata viviparum chose the high P-content algae, whereas Theodoxus fluviatilis had no preference and Bythinia tentaculata, a more sedentary species, did not discriminate between food items. The second experiment (6 d) dealt with the influence of grazing by these same three snails on periphytic biomass and algal growth forms. A shift in algae composition, removing unicellular with raphe and chains diatoms to allow green colonies to grow up, was caused by T. fluviatilis and less intensely by V. viviparum, but not by B. tentaculata. The biomass of the periphyton was not significantly affected, probably because of the short duration of this experiment. Experiment three studied the impact of grazing in a long-term laboratory experiment (23 d) on epilithic periphyton with two different grazers (T. fluviatilis and B. tentaculata). The biomass of the periphython decreased in the "grazed" treatments. Moreover, grazing enhanced the spatialheterogeneity of periphton. This decrease of difference of Chi.a was not explained by the distances between each tile. The snails grazed periphyton in a homogeneous way: they were not concentrated to feed on the algae, which were close to each other. The grazing pressure of these two snails and its effetcs on spatial heterogeneity were similar
| la date de réponse | 2002 |
|---|---|
| langue originale | Anglais |
| Superviseur | Jean-Pierre DESCY (Promoteur) |