Modelling the Fundamental Niche to Predict the Effects of Climate Warming on Interactions Between Native and Invasive Mussels in South Africa

ABSTRACT Aim Climate change is reshuffling the distribution of species globally and threatening to modify the structure and functioning of natural and managed ecosystems. Most studies predicting species distributions rely on statistical approaches that do not capture the species' fundamental niche. In contrast, energy budget models include lethal and sublethal levels of stress to explore traits, such as growth and reproduction, that drive ecological responses. We used models parameterised for two competing intertidal mussels, the native Perna perna and the invasive Mytilus galloprovincialis , to investigate their current and projected distributions. Location South African rocky shores. Taxa Mussels, Mytilus galloprovincialis and Perna perna . Methods We used previously parameterised dynamic energy budget (DEB) models. Model predictions were validated using a 2‐year dataset describing current conditions (body temperature and chlorophyll‐ a concentration) and fitness‐related traits (growth and reproductive effort) at nine sites: three western sites inhabited by Mytilus alone, three eastern sites occupied by Perna and three southern sites where the species coexist. We then tested the effects of three climate change scenarios on the model predictions of maximum size, growth rate and gonadosomatic index around South Africa. Results Current spatial patterns are likely to be maintained until the century's end, and the physiological mechanisms presently excluding Mytilus from the east coast (impaired growth due to food limitation) and Perna from the west coast (impaired reproduction due to cold temperatures), will continue to operate until the end of the century. Our model also revealed a possible change in the competitive hierarchy between these species as warming will favour the reproductive potential of Perna more than that of Mytilus . Conclusion Our approach of exploring the fundamental niche rather than using a statistical approach suggests that the effects of projected temperature conditions on the distributions of these species will be less severe than expected.