Positive relationships between interspecific association strength and elevational range overlap highlight the role of facilitation in community assembly

The interplay of abiotic conditions and biotic interactions determines individual species' ranges, and by extension therefore, community assembly. To date, studies have focused predominantly on abiotic filtering (e.g., temperature) and agonistic interactions (e.g., competition) as potential drivers of community assembly; the role of facilitation in setting geographical range limits and structuring communities remains unclear. We tested how participation in compositionally distinct modules of facilitative networks of interactions in mixed-species bird flocks (MSFs) influenced interspecific elevational range overlaps across a 2000m elevational gradient in the hyperdiverse Eastern Himalaya. Species that participated in MSFs had higher average elevational range overlap compared with MSF non-participants. Positive correlations between pairwise association strength in MSFs and elevational range overlap were found for all MSF modules. We highlight the potential role of facilitation in determining species co-occurrence patterns and assembling communities across large spatial gradients.