Figure 1 Effects of shading and snail biomass on primary producers. P. crispus shoot biomass (A) , V. spinulosa biomass (B) , periphyton chl a content (C) , and phytoplankton chl a content(D) . S0 indicates full light, S1 indicates low light intensity under shading. Lines are fitted by gam functions in package ggplot2, and a solid line indicates p < 0.05, and a dashed line indicatesp > 0.05. Dot symbol indicates nutrient loading, and triangles indicate no additional nutrients were added. P values in the panel indicate a significant effect of shading on the mean of the response variable.