Figure 4 Structural equation model (SEM) of shading, nutrient loading and snail biomass effects on the growth of primary producers. Exogenous variables are indicated by rounded rectangles, and endogenous variables are represented by ovals. Coefficients of determination (r 2) are shown for all endogenous variables. Numbers adjacent to arrows are standardized path coefficients and indicate the effects of the relationship. Positive and negative effects among variables are depicted by green and orange arrows, respectively, with arrow thicknesses proportional to the strength of the relationship. Significant pathways (p < 0.05) are represented by solid lines, otherwise by dashed lines. The model satisfied each of the three model fit criteria with significant χ2 ofp = 0.239, standardized root mean squared residuals of 0.012, and comparative fit index values of 0.981.