Species competing for resources also commonly share predators. While competition often drives divergence between species, effects of shared predation are less understood. Theoretically, competing prey species could either diverge or evolve in the same direction under shared predation depending on the strength and symmetry of their interactions. We took an empirical approach to this question, comparing antipredator and trophic phenotypes between sympatric and allopatric populations of threespine stickleback and prickly sculpin fish that all live in the presence of a trout predator. We found divergence in antipredator traits between the species: in sympatry, antipredator adaptations were relatively increased in stickleback but decreased in sculpin. Shifts in feeding morphology, diet and habitat use were also divergent but driven primarily by stickleback evolution. Our results suggest that asymmetric ecological character displacement indirectly made stickleback more and sculpin less vulnerable to shared predation, driving divergence of antipredator traits between sympatric species.

This repository contains the data and R-codes used for Roesti et al. ("Species divergence under competition and shared predation", Ecology Letters). Details can be found in the accompanying README file and in the Methods section of the publication. If you are using any of these data or codes, please cite Roesti et al. and this repository.