Recent evidence is casting doubt on the assumption that competition has a limited role in influencing diversity at large spatial scales. Here, we test how species interactions (competition and predator-prey) influence the ranges of individual species and how this scales up to diversity within areas (e.g. species richness). To do this, we couple a newly assembled food web for all European vertebrates with species distribution information, and use statistical models to quantify the effect of species interactions (derived from the food web) as well as climate on the species distributions. We then use the models to predict what would happen to species if we increase prey or decrease competition. Finally, we scale up these scenarios for a prediction of how lessening competitive pressure or resource constraints might change species richness across Europe.
Results/Conclusions
In general, we find that a species is more likely to occur if their prey species are present, but less likely to occur if their competitors are present (while considering the effect of other interactions and climate). This suggests that competition in particular is acting to limit the distributions of species from otherwise suitable climate space. By ‘releasing’ competition (setting the competition term to zero), most species greatly expand their range. This effect scales up, such that the models suggest species richness is limited by competition, especially in already diverse, climatically moderate areas—linking theory on species niches and species richness gradients.