The Impact of a Range-Shifting Predator Is Affected by Prey Preference and Composition

Global biodiversity is undergoing a grand reshuffling with species across taxa and biomes shifting their ranges in response to climate change. Research on the ecological impacts of range-shifting species has prioritized linking the traits of the range-shifting species themselves to impacts, with studies giving more limited attention to the characteristics of the recipient community and its prey composition. Understanding how community composition and structure can alter the impact of novel species via prey preferences is important for predicting and managing ecological changes. We used the range-shifting predatory whelk Mexacanthina lugubris as a case study to investigate how prey composition might influence prey preferences and overall range shift impacts on prey species. Specifically, we hypothesized that Mexacanthina lugubris' consumptive effects on a single prey species would be modified by the presence (or abundance) of a second prey species. We tested this hypothesis via a field experiment in southern California, where we caged whelks at a gradient of densities and observed their predation on mussels, barnacles living on bare rock, and barnacles living on mussels over 8 weeks. We found that Mexacanthina lugubris consumed barnacles on bare rock preferentially before consuming barnacles on mussels and mussels themselves. Our findings demonstrate that the presence of mussels (which act as both habitat and prey) can mitigate the overall impact of the range-shifting predator by altering accessibility of barnacle prey. This context-dependent attenuation of predator impacts highlights a form of apparent facilitation among prey and underscores the importance of considering recipient community traits when assessing or managing the ecological consequences of range-shifting species.