Patch size distribution and network connectivity affect species invasion dynamics in dendritic networks

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.