Positive interactions support complex networks

Ecologists have recognised the effects of biotic interactions on the spatial distribution of living organisms. Yet, the spatial structure of plant interaction networks in real-world ecosystems has remained elusive so far. Using spatial pattern and network analyses, we found that alpine plant communities are organised in spatially variable and complex networks. Specifically, the cohesiveness of complex networks is promoted by short-distance positive plant interactions. At fine spatial scale, where positive mutual interactions prevailed, networks were characterised by a large connected component. With increasing scale, when negative interactions took over, network architecture became more hierarchical with many detached components that show a network collapse. This study highlights the crucial role of positive interactions for maintaining species diversity and the resistance of communities in the face of environmental perturbations.