Abstract
Protecting habitat and the species they shelter by setting up protected areas (PAs) has become a conservation priority to mitigate the current extinction crisis. This strategy has improved different aspects of biodiversity including species richness and abundance across ecosystems. However, to truly understand the effectiveness of mitigation measures against global environmental change, we must account for one of the fundamental dimensions of biodiversity: species interactions. Using 376 556 curated citizen science records of 509 bird species distributed across 45 networks of European PAs (collections of connected PAs), we show that the effects of PAs on the structure of avian food webs are mixed across Europe. Overall effects of protection include an increase in species richness and larger body masses of both top and intermediate species. For other food web features, the sign and magnitude of the effects are mixed. Our results further suggest that these effects are strongly influenced by geographical and environmental features of the PA networks such as remoteness, habitat diversity, human pressure and agriculture. Lastly, PAs with specific protection goals such as those administered by European Bird Directives for conservation sustain more complex food webs. Our study provides evidence for the need of including clear management goals and considering environmental context in the designation of PAs to increase their effectiveness at preserving biodiversity beyond species richness.