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bioRxiv · 10.64898/2025.12.16.694722

The Goldilocks effect drives plant diversification on middle-aged Hawaiian islands

Lichter-Marck, I.·Swiston, S. K.·Mendes, F. K.·May, M. R.·Neupane, S.·Baldwin, B. G.·Wood, K.·Ronsted, N.·Wagner, W. L.·Zapata, F.·Landis, M. J.
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Abstract

Islands are natural laboratories for studying dispersal, speciation, and extinction, yet the historical dynamics of many insular radiations remain poorly understood because of the difficulty aligning the tempo and mode of diversification with paleogeography during phylogenetic inference. We introduce a phylogenetic modeling framework, named TimeFIG, that combines data about species ranges and genetic variation with paleogeographic information to simultaneously infer divergence times, ancestral ranges, and historical diversification rates, without relying on fossils to time-calibrate the phylogeny. Applying TimeFIG to the spectacular radiation of Hawaiian Kadua (Rubiaceae) points to colonization of either modern Kaua'i or ancient now-eroded islands, with island isolation as the strongest correlate of dispersal, and with a tendency for net diversification to be highest on "middle-aged" islands. Modeling diversification within an explicit spatiotemporal context, while accounting for historical uncertainty regarding the timing and placement of phylogenetic and biogeographic events, enables the rigorous testing of foundational hypotheses in island biology and evolutionary theory for clades beyond Kadua.

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Lichter-Marck, I., Swiston, S. K., Mendes, F. K., May, M. R., Neupane, S., Baldwin, B. G., Wood, K., Ronsted, N., Wagner, W. L., Zapata, F., Landis, M. J.. 2025-12-19. The Goldilocks effect drives plant diversification on middle-aged Hawaiian islands. https://doi.org/10.64898/2025.12.16.694722

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