A male ornate wrasse Thalassoma pavo, a warm-water fish, which is the ‘winner’ species dominating the best quality habitat at the expense of the ‘loser’ species, a cool-water wrasse Coris julis, under conditions of warming. Photo by Agostino Tomasello. Milazzo, M., Mirto, S., Domenici, P. & Gristina, M. (2013) Climate change exacerbates interspecific interactions in sympatric coastal fishes. Journal of Animal Ecology, 82, 468–477. Species interactions have received little attention in climate-change studies, yet these interactions are fundamental to the functioning of ecosystems. Milazzo et al. (2013) combined field surveys and controlled experiments to show how increasing abundance of a range-extending species and ocean warming interactively affect the habitat occupancy of two co-occurring species with similar habitat preferences. The authors found that in warmer conditions the ‘cool-water’ species is competitively displaced from preferred algal habitat to sub-optimal seagrass habitat, but only at higher densities of the warm-water species. Their results provide an important first step for unravelling how simple species interactions can create novel communities.