Predicting species response to climate change: The role of evolutionary relatedness, environmental distribution, and physiology
Despite accumulating evidence that species respond individualistically to climate change, species performance may be predicted given a set of known ecological and evolutionary relationships. However, few studies have attempted to experimentally disentangle the factors that shape the climate change response of related species in a community. We tested whether the response of key physiological rates to ocean acidification in a guild of calcifying marine algae could be predicted from either phylogenic relationships, distributional patterns across environmental gradients, or baseline physiological traits. Specifically, we tested how net calcification, photosynthesis, and growth rates respond to ocean acidification in five species of rocky intertidal articulated coralline algae (family: Corallinales). We conducted a series of ocean acidification laboratory experiments, exposing species to increased pCO2 in a regression design from preindustrial levels (~285 ppm CO2) to ~2500 ppm. Several short term experiments and one long term experiment were conducted in a mass-flow controlled acidification system. Net calcification and photosynthesis rates were measured using the alkalinity anomaly method, where rates are calculated from the change in total alkalinity and dissolved inorganic carbon of the surrounding seawater of each sample during each experiment. Net growth was assessed over the long-term experiment using fluorescent staining.
In this study, we characterized the physiological response of five species of coralline algae to ocean acidification, four of which have never been studied for their acidification vulnerability. As expected, though there were species-specific differences in calcification, species generally decreased their net calcification and growth and increased their net photosynthesis with increasing pCO2. Our surveys of the distribution of these five species in the field revealed that congeners were rarely found co-occurring. However, despite this strong separation of congener species across habitats, preliminary results indicate that phylogenetic relationships were more important than environmental distribution or baseline physiological rates alone for predicting species response to ocean acidification. For example, during the long-term experiment, the shape of the functional response of growth rate to increasing pCO2 differed among genera, but not among species within genera that differed in their habitat distribution. Together, these results demonstrate the importance of shared evolutionary history in mediating individual physiological responses to a climate stressor. More generally, although species differ in their baseline metabolic rates, the functional response of these rates to climate change may be predictable from phylogenetic or ecological information, potentially reducing the information needed to make accurate predictions about community response to climate change.