Hybrid zones occur as range boundaries for many animal taxa. One model for how hybrid zones form and stabilize is the tension zone model, a version of which predicts that hybrid zone widths are determined by a balance between random dispersal into hybrid zones and selection against hybrids. Here, we examine whether random dispersal and proxies for selection against hybrids (genetic distances between hybridizing pairs) can explain variation in hybrid zone widths across 131 hybridizing pairs of animals. We show that these factors alone can explain ~40% of the variation in zone width among animal hybrid zones, with dispersal explaining far more of the variation than genetic distances. Patterns within clades were idiosyncratic. Genetic distances predicted hybrid zone widths particularly well for reptiles, while this relationship was opposite tension zone predictions in birds. Lastly, the data suggest that dispersal and molecular divergence set lower bounds on hybrid zone widths in animals, indicating there are geographic restrictions on hybrid zone formation. Overall, our analyses reinforce the fundamental importance of dispersal in hybrid zone formation, and more generally in the ecology of range boundaries.

These data were culled from a meta-analysis of over 150 studies of 131 hybrid zone systems.

Also included are the scripts available on GitHub, zipped for archival purposes: https://github.com/singhal/hz_metaanalysis 

Data on column descriptions are available as Appendix Table A1 & A2. Inline citations are referenced in the 'References for Online Enhancement Only'.