Climate Driven Range Shifts Impact Communities Through Altered Species Interactions
Climate change is likely the greatest threat to global biodiversity and ecosystem functioning, and it is becoming increasingly apparent that understanding the effects of climate change requires going beyond single species or limited spatial scales. Climate change will impact species and communities through both direct and indirect effects, as mediated by species interactions, and incorporating these indirect effects can increase the ability to track shifting species distributions. I used a space-for-time approach to test if incorporating indirect effects increases predictive ability through surveys of vertical distributions of predators (sea stars) and prey species (mussels) spanning a thermal gradient along the West Coast. Prey distributions were directly influenced by temperature, but there was also a significant indirect effect of temperature, as mediated by predator distributions. Under future climate change, mussel ranges may undergo vertical shifts towards subtidal habitats, allowing for localized persistence of mussels and their associated species. However, both local and broad scale range-shifts can displace other species or alter community and ecosystem processes. Despite inherent differences between introduced and range-shifting species, impacts can occur via analogous mechanisms, and the magnitude of impacts can be similar. Risk assessments developed for invasive species provide a useful tool for assessing potential impacts of range-shifting species. Altered species interactions and communities can be observed locally in southern California intertidal communities, where the whelk Mexacanthina lugubris is undergoing a northward range shift. I assessed the impacts of Mexacanthina on local species, through long-term field surveys, coupled with manipulative experiments to assess current and future impacts on competitors. Mexacanthina is now well established and utilizes analogous resources and habitats as native whelk species. Mexacanthina can also survive at warmer temperatures than native whelks, suggesting that range-shifters may have a competitive advantage in a warming climate. The persistence of some species at the expense of others underscores the complexities of conservation in the era of climate change. My thesis research explores this dichotomy by examining how species interactions can indirectly alter distributions (Ch. 1), which traits are indicative of problematic range-shifters (Ch. 2), and how a range-shifting species is altering southern California communities (Ch. 3).