FIGURE 6.

Predicted (black lines) and observed (symbols) competition coefficients between Phaeodactylum tricornutum and Thalassiosira pseudonana across assay temperatures in (a) high N conditions and (b) low N conditions. A coefficient of 0 indicates no competitive advantage for either species and predicts stable coexistence under the assay conditions. At coefficients greater than 0, Phaeodactylum tricornutum has the competitive advantage, and at coefficients below 0, Thalassiosira pseudonana has the advantage. The further the competition coefficient deviates from 0, the stronger is the competition between the two species. In (a), the solid black line indicates predictions for competition coefficients made from high N monoculture growth rates. The solid blue line is the LOESS smooth to visualize the progression of all observed high N competition coefficients across temperatures (R² = 0.97, RSE = 0.047). Observed coefficients were calculated from changes in species frequencies over time in mixed cultures (data from Figure  S10 ), calculated with Equation ( 5 ). Closed symbols represent the competition coefficients that were started when stock cultures were transferred to the temperature‐gradient block, open symbols those that were started 2 weeks later to investigate the potential effects of temperature acclimation. In (b), solid black line indicates predictions made from the initial exponential growth rate in low N medium for monocultures, whereas the dashed line indicates predictions made from monoculture carrying capacities across the temperature gradient. The solid blue line is the LOESS smooth to visualize the progression of all observed low N competition coefficients across temperatures (R² = 0.86, RSE = 0.051). Observed coefficients were calculated from changes in species frequencies over time in mixed cultures (data from Figure  S11 ), calculated with Equation ( 5 ). Closed symbols represent competition replicates that were started at the onset of N limitation, and open symbols those that were started from monocultures that were cultured under N limitation for an additional 7 days