Influence of vegetation cover on the biological traits of pond invertebrate communities

Without human intervention, ponds progressively fill up with aquatic vegetation, so that the structure and age of the vegetal formations show great contrasts within a given set of water bodies. We hypothesized that the biological traits of pond invertebrate communities differed significantly among ponds having different vegetal formations. To test this hypothesis, we selected three neighbouring ponds showing a gradient of vegetation cover and type (sparse bryophytes on rocky substrata (pond 1), extensive submerged Chara beds (pond 2), aerial Typha stands (pond 3)), and we studied between-ponds variations in the combinations of species traits. Taxa biomass was monthly recorded in each pond over one year, to take into account species' seasonality. Species traits were described using a fuzzy-coding method and a simultaneous analysis of the two matrices (co-inertia analysis) was used to investigate changes in biological trait composition. Biomass increased from pond 1 to pond 3, and was higher in vegetal than in muddy mesohabitats. Among 25 biological traits, 10 were significantly correlated to the distribution of samples: number of generations per year, cohort production interval, adult longevity, adult size, number of eggs per female, dispersal ability, dispersal mode, consumer level, ingested food type, and feeding group. Invertebrates in pond 1 species allocated much energy to reproduction, while in pond 3 resource use was favoured by larger body size, long-lived organisms, and a higher diversity of feeding groups. Our results suggest that the structure and age of the vegetal formation play role in selecting species traits related to population dynamics and feeding habits.