Disturbances as a structuring factor of plant palatability in aquatic communities

Plant palatability plays an important part in the fitness of species and is therefore regarded as a key functional trait. The aim of this study was to relate the palatability of aquatic macrophytes to their distribution in riverine wetlands differing in their exposure to spate flood disturbances. Thirty-three former channels of the Rhone River Basin (eastern France) were characterized in terms of flood-disturbance level. Nutrient richness was also measured to eliminate its potential confounding effect. The coverage of 40 macrophyte species was recorded in these wetlands, and their palatability was assessed through laboratory feeding trials using a generalist consumer, the pond snail Lymnaea stagnalis. The consumption rate of L. stagnalis ranged from 3.9 mg (.) g(-1) (.) d(-1) (for Hottonia palustris) to 137.9 mg (.) g(-1) (.) d(-1) (for Sagittaria sagittifolia) and was used as a palatability index. Plant palatability was unrelated to the nutrient richness of sites but was positively correlated with their flood-disturbance level. However, the strength of this correlation decreased as nutrient richness increased. These results suggest that spate floods promote functional diversity in riverine wetlands, allowing the persistence of the most palatable plant species otherwise eliminated by herbivores, especially in nutrient-poor habitats.