Competition alters species' plastic and genetic response to environmental change

Species react to environmental change via plastic and evolutionary responses. While both of them determine species’ survival, most studies quantify these responses only individually. As species occur in communities, competing species may further influence their respective response to environmental change. Yet, how environmental change and competing species combined shape plastic and genetic responses to environmental change remains unclear. Quantifying how species interactions such as competition alter plastic and genetic responses of species to environmental change requires integrating approaches from trait-based, community and evolutionary ecology. We exposed unicellular aquatic organisms to long-term selection of increasing salinity—representing a common and relevant environmental change. Then, we assessed plastic and genetic contributions to phenotypic change in biomass, cell shape, and dispersal ability along increasing levels of salinity in the presence and absence of competition. Species differed in their response to salinity and to competition. The observed trait changes during selection were mainly due to mean trait evolution, and differed whether species evolved in the presence or absence of competition. Moreover, our results show that species’ evolutionary and plastic responses to environmental change depended both on the presence of competing species and the magnitude of the environmental change, ultimately determining species persistence. Our results suggest that understanding plastic and genetic responses to environmental change within a community will improve predictions of species’ persistence to environmental change.