When environments change sequentially, past conditions can leave legacies that modify population growth and trait expression under subsequent stress. Under global change, sequences such as marine heatwaves followed by pollution runoff increase the likelihood and consequence of such legacies for population and community dynamics. We tested for sequence‐dependent legacy effects in six globally distributed strains of the marine phytoplankton Synechococcus sp. using a full‑factorial microcosm experiment with warming, herbicide pollution, and control treatments as both chronic (constant) and sequential (changing) exposures. We quantified chronic and acute sensitivities as changes in population density, per capita growth rate, cell size and chlorophyll content following respective exposures. Significant chronic sensitivity occurred in 58.3% of strain–exposure combinations and significant acute sensitivity in 48%; acute responses often showed decoupling between growth and traits. Comparisons of chronic and acute sensitivities demonstrate that past environments systematically alter subsequent responses, producing strain‑ and exposure‑specific overcompensation or undercompensation. Consequently, incorporating sequence‐based legacies into predictions of biodiversity dynamics and ecosystem function under global change is essential.
Sikder et al. (Fri,) studied this question.