Climate drives community-wide divergence within species over a limited spatial scale: evidence from an oceanic island

Geographic isolation substantially contributes to species endemism on oceanic islands when speci-ation involves the colonisation of a new island. However, less is understood about the drivers ofspeciation within islands. What is lacking is a general understanding of the geographic scale of gene flow limitation within islands, and thus the spatial scale and drivers of geographical specia-tion within insular contexts. Using a community of beetle species, we show that when dispersalability and climate tolerance are restricted, microclimatic variation over distances of only a fewkilometres can maintain strong geographic isolation extending back several millions of years. Fur-ther to this, we demonstrate congruent diversification with gene flow across species, mediated byQuaternary climate oscillations that have facilitated a dynamic of isolation and secondary contact.The unprecedented scale of parallel species responses to a common environmental driver for evo-lutionary change has profound consequences for understanding past and future species responsesto climate variation