Protected areas (PAs) are a key element of global conservation strategies aiming to protect habitats and species from various threats such as non-natives species (NNS) with negative ecological impacts. Yet little is known about the mechanisms by which PAs are colonized by NNS, and more specifically the role of colonizing events from surrounding areas. Here, we compared terrestrial and freshwater non-native plants and animals recorded in Norwegian PAs and in 5-km belts around them, using the database of the Norwegian Biodiversity Information Centre Species Map Service. Our analysis included 1,602 NNS and 671 PAs. We found that NNS were recorded in only 23% of the PAs, despite the fact that 90% of the 5-km belts were colonized by at least one NNS. A Zero-inflated negative binomial regression model showed that the number of NNS in the 5-km belts was a strong explanatory variable of the NNS richness inside PAs. Other significant variables included the surface area of the PA, mean human population density in the PA, main type of habitat and accessibility of PAs. We also observed similarity in the species in and around the PAs, with, on average, two thirds of the NNS present in a specific PA also present in its 5-km belt. Furthermore, NNS were recorded in PAs on average 4.5 years after being recorded in the 0–5 km belts, suggesting a dynamic of rapid colonization from the belts to the PAs. Invasive NNS represented 12% of NNS in the belts but 40% in the PAs. This difference was related to the higher abundance of invasive NNS in the belts. Our results highlight the necessity of expanding the focus of NNS management in PAs beyond their boundaries, in particular to prevent incursions of NNS with high negative ecological impact.

Biological invasions are globally affecting ecosystems, causing local species loss and altering ecosystem functioning. Understanding how such biological invasions occur and succeed is thus of high priority. Both local properties and the spatial network structure have been shown to be determinants of invasion success, and the identification of spatial invasion hubs directly promoting invasion dynamics is gaining attention. Spatial dynamics, however, could also indirectly alter invasion success by shaping pre‐invasion local community structure: in many ecosystems, such as riverine networks, regional properties such as patch size distribution are known drivers of local community structures, which themselves may affect the establishment success of invading species. Using microcosm experiments in dendritic networks, we disentangled how inherent patch size distribution and dispersal along specific network topologies shaped local resident communities, and, subsequently, affected the establishment success of invading species. After controlling for regional scale effects of connectivity on pre‐invasion diversity, we find that patch size distributions independently shaped pre‐invasion community diversity and invasion success, with no direct effect of pre‐invasion diversity on invasion success. Our results suggest that 1) landscape configuration plays an underestimated role in invasion success and that 2) invasion success should follow predictable landscape‐scale patterns in riverine networks given non‐random patch‐size distribution.

Biological invasions are globally affecting ecosystems, causing local species loss and altering ecosystem functioning. Understanding the success and unfolding of such biological invasions is thus of high priority. Both local properties and the spatial network structure have been shown to be determinants of invasion success, and the identification of spatial invasion hubs directly promoting invasion dynamics is gaining attention. Spatial dynamics, however, could also indirectly alter invasion success by shaping local community structure: in many ecosystems, such as riverine networks, regional properties such as patch size distribution are known drivers of local community structures, which themselves may affect the establishment success of invading species. Using microcosm experiments in dendritic networks, we disentangled how patch size distribution and dispersal along specific network topologies shaped local communities, and, subsequently, affected the establishment success of invading species. We find that inherent patch size distributions shaped composition and diversity of local communities, and, subsequently, modulated invasion success. Specifically, the relationship between local diversity and invasion success changed across an increasing patch size gradient from a negative to a positive correlation, while overall increasing patch size reduced invasion success. Connectivity did not have a direct effect on invasion success but indirectly affected invasions by shaping diversity patterns in the whole network. Our results emphasize the relevance of indirect, landscape-level effects on species invasions, which need to be considered in the management of spatial habitat networks.