Figure 1

Canonical correspondence analysis (CCA) of mollusk communities: (a) classification diagram of sampling sites based on period (as predictors): T1—XIXth century, T2—1995–2000, T3—2020 (adjusted explained variation 23.6%; first axis accounts for 17.6% the second for 6.0%, both axes are significant, p = 0.001); (b) CCA diagram of species occurrence constrained by environmental predictors (period, habitat: L—lakes, lentic sector in reservoirs, R—river, lotic sectors, and Impact—human impact) with functional diversity expressed as Rao quadratic entropy index (FD (Rao)) isolines plotted by generalized additive models (GAM) on the ordination space (adjusted explained variation 28.36%; first axis accounts for 16.3%, the second for 6.0%, both axes are significant, p = 0.001) .