Figure 2.

Relationship between the proportion of ineffective nodules and shoot biomass in the mixed and mutualist treatment, demonstrating the cost of assortative preference with mutualist rhizobia. Each dot is a line mean. Line means for exploiter occupancy (estimated in the mixed treatment) are correlated with the corresponding line means for plant biomass in the absence of exploitation (mutualist treatment, dashed line). A positive correlation shows a cost to increasing associations with beneficial partners, but our data indicate no significant positive or negative associations with these traits (dashed line, open circles). The relationship between shoot biomass in the mixed treatment and exploiter occupancy (solid line, closed circles) is shown for comparison.