Host performance
The RGR was nearly 50% higher among algae at 15 °C compared to 22 °C and more than five-fold higher in non-natives compared to natives (p < 0.001, Figure 2A, B), but the interaction term was not significant (see Table S2a for all statistical output). Photosystem II quantum yields did not vary between temperatures or ranges. Of the observed disease symptoms, the thallus brittleness was more prevalent at 22 °C and more common among non-native algae (p < 0.001, Figure 2C, D) but did also not yield a significant interaction term. The observed thallus decay was overall low and did not vary with range or temperature. There were no strong correlations among the four response variables (maximum ρ = 0.31, between yield and thallus brittleness).