Figure 6

Pesticide pollution favors tolerant snails over less tolerant competitors. (a) No significant change in the community composition of grazers, predators and other taxa with pesticide pollution (PERMANOVA; n = 48, F = 0.80, res. df = 46, p = 0.502, R² = 0.02). For the graph, the range of TU_max values was evenly split in three categories, and for each pollution category the mean proportion of each guild on the macroinvertebrate community is shown. Because some taxa belong to more than one guild, we calculated proportions as the individuals in a guild divided by the summed-up individuals in all guilds (≠ the total individual number) so that the proportions sum up to 1. (b) Within the guild of grazers, the dominance of snails increases with pesticide pollution (n = 47, χ² = 13.82, res. df = 45, p < 0.001, McKelvey-Zavoina’s pseudo-R² = 0.37). One site was omitted because no grazers were found. Quasi-binomial GLM with logitlink function; means ± 95% confidence intervals are shown.