Role of biotic interactions in patterning epiphytic diatoms assemblages
Rôle des interactions biotiques sur les assemblages d'espèces des diatomées épiphytiques
Résumé
Although relationships between aquatic organisms and environmental variables are usually well studied in lakes, the contribution of biotic relationships is rarely considered for explaining diversity patterns. Here we aimed to evaluate whether environmental variables and epiphytes interactions with other aquatic communities drive the diversity patterns of epiphytic diatom communities. More precisely we tested a substrate effect of macrophytes and mechanisms of facilitation, competition and predation with phytoplankton and micro-meiofauna. During one year, we sampled epiphytic diatoms on 5 different macrophytes species in 6 stations of one large and shallow lake, and estimated their biomass, richness and taxonomic composition. We then tested how these measures vary according to season, water physico-chemical composition, macrophyte species colonized, epiphytic heterotrophic biomass and phytoplankton composition. We found significant variation in diatom biomass and richness according to season and water chemistry, but also according to their host plant and particularly to the macrophyte stature. We also found some positive influence of grazers and phytoplankton on diversity, but evidenced limited competition mechanisms with phytoplankton. These results suggest that epiphytic diatoms communities are not only patterned by environmental conditions, but that biotic interactions also play a determining structuring role.