Trait-dependent species responses weaken the effects of response diversity on community stability

The diversity of species responses to environmental change (response diversity) is a key mechanism of ecological stability. However, anticipating where strong or weak stabilizing responses emerge is challenging because species responses can depend on the local community and the specific stability metric. Whether species traits can consistently inform on how species respond to disturbances, enabling less context-dependent predictions, remains an open question. To address this gap, we use microcosm experiments on marine phytoplankton to test how response diversity supports multiple aspects of community stability under pulse temperature changes, testing both an increase (heatwave) and a decrease in temperature (coldspell). We then map species traits to their responses in a community to identify which traits modulate and predict species' sensitivities. Fundamental response diversity, based on the diversity of species responses to temperature measured in isolation, was a weak predictor of community stability, and relationships differed between disturbances (i.e., heatwave and coldspell). Instead, species traits were consistent predictors of species responses in communities. Small, fast-growing species were more tolerant and benefited from the disturbance, while large, slow-growing species were less tolerant and decreased in proportion - these patterns were consistent across disturbances and community compositions. These results suggest that strong trait-performance relationships might reduce the importance of response diversity for stability. But these findings also show that general species traits, such as size and growth rate, can predict which species, and how, contribute to community responses, providing an empirical basis to relate species traits to stability outcomes under climate change.