The biogeography of evolutionary radiations on oceanic archipelagos

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1. Version published to 10.24072/pcjournal.688

   Mar 16, 2026
2. 

   Peer Community in Ecology

   Jul 18, 2025

   Island biogeography has long inspired theory, yet quantitative tests of how within-radiation diversity scales with island properties remain scarce. Brée et al. (2024) assembled a nicely curated dataset of 95 evolutionary radiations (ROAs) distributed across four classic volcanic archipelagos—Hawaii, the Canary Islands, the Galápagos and Fiji—encompassing vascular plants, invertebrates and vertebrates. By pairing island-specific species counts for each radiation with a common suite of geo-environmental descriptors, the authors ask two deceptively simple questions: (i) which island traits best explain richness patterns inside radiations, and (ii) does the strength of those effects vary among archipelagos and broad taxonomic groupings?
   Across the whole dataset, maximum elevation emerges as the most frequent and robust positive predictor of …

   Island biogeography has long inspired theory, yet quantitative tests of how within-radiation diversity scales with island properties remain scarce. Brée et al. (2024) assembled a nicely curated dataset of 95 evolutionary radiations (ROAs) distributed across four classic volcanic archipelagos—Hawaii, the Canary Islands, the Galápagos and Fiji—encompassing vascular plants, invertebrates and vertebrates. By pairing island-specific species counts for each radiation with a common suite of geo-environmental descriptors, the authors ask two deceptively simple questions: (i) which island traits best explain richness patterns inside radiations, and (ii) does the strength of those effects vary among archipelagos and broad taxonomic groupings?
   Across the whole dataset, maximum elevation emerges as the most frequent and robust positive predictor of intra-radiation richness. I find this result persuasive because it echoes broader evidence that steep environmental gradients boost speciation by multiplying ecological opportunities (Barajas-Barbosa et al. 2020; Steinbauer et al. 2016).
   Although elevation dominates overall, the strength and sign of other drivers vary with geological context. In Hawaii, richness tends to rise with island area and with a measure of topographic complexity, whereas in the Canaries a hump-shaped relationship with island age combines with a negative effect of inter-island isolation; Fiji shows a similarly strong age signal but little isolation effect, and the Galápagos yield no single dominant factor. Such contrasts fit neatly within the general dynamic model oceanic island biogeography, which predicts that the diversification process shifts as islands move through their ontogeny (Whittaker et al. 2008).
   A notable virtue of the study is its resolution at the level of clades rather than whole biotas. Treating each radiation as an independent replicate avoids the taxonomic pooling that can obscure lineage-specific responses. For example, Brée et al. (2024) show that elevation effects are stronger for plant radiations than for invertebrates in the Canaries but not in Hawaii, demonstrating an interaction between intrinsic life-history traits and extrinsic environment.
   The authors candidly discuss limits of coverage—Hawaii and the Canaries still dominate island-radiation research and explain why formal classification of speciation modes was premature given current phylogenetic evidence. Time since colonisation, although difficult to estimate consistently, could further refine the observed age–diversity relationships. Even so, the present analysis already sets a benchmark for clade-level biogeographic modelling.

   
   In sum, I am pleased to recommend this pre-print as it demonstrates convincingly that vertical relief—and the ecological heterogeneity it proxies—serves as the principal engine of speciation on young oceanic islands, while the influence of area, age and isolation is contingent on geological history and lineage traits. Their synthesis advances island biogeography by moving beyond the classical focus on total species counts to illuminate the environmental controls on diversification within lineages. This work will interest researchers in macroevolution, community ecology and conservation, and it supplies a rich openly accessible dataset for future comparative work.

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   The data editor's report can be found below:

   Editor: Matthias Grenié

   1. Data

   Data and metadata must be archived and adhere to FAIR guiding principles

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   Archived data corresponds with the data reported in the manuscript

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   2. Code

   Code and metadata must be archived and adhere to FAIR guiding principles

   [x] Code has a repository

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   [x] Code files are present in the repository

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   Archived code matches the manuscript

   |x] Code is present for all analyses in the manuscript, along with code used to produce figures/tables where appropriate

   
   Archived code runs with the archived data

   [x] Runs without errors

    

   3. Computational reproducibility

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   Comments from the data editor:

   Thank you for sharing your data and code openly!

   All of the analyses ran fine on my machine without a bug and the last minor details have now been fixed.

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   References

   Baptiste Brée, Thomas J. Matthews, José María Fernandez-Palacios, Christian Paroissin, Kostas A. Triantis, Robert J. Whittaker, François Rigal (2024) The biogeography of evolutionary radiations on oceanic archipelagos. bioRxiv, ver.2 peer-reviewed and recommended by PCI Ecology https://doi.org/10.1101/2024.10.07.616413

   Barajas-Barbosa, M. P., Weigelt, P., Borregaard, M. K., Keppel, G., & Kreft, H. (2020). Environmental heterogeneity dynamics drive plant diversity on oceanic islands. Journal of Biogeography, 47(10), 2248–2260. https://doi.org/10.1111/jbi.13925 

   Steinbauer, M. J., Field, R., Grytnes, J.-A., Trigas, P., Ah-Peng, C., Attorre, F., Birks, H. J. B., Borges, P. A. V., Cardoso, P., Chou, C.-H., De Sanctis, M., de Sequeira, M. M., Duarte, M. C., Elias, R. B., Fernández-Palacios, J. M., Gabriel, R., Gereau, R. E., Gillespie, R. G., Greimler, J., … Beierkuhnlein, C. (2016). Topography-driven isolation, speciation and a global increase of endemism with elevation. Global Ecology and Biogeography: A Journal of Macroecology, 25(9), 1097–1107. https://doi.org/10.1111/geb.12469

   Whittaker, R. J., Triantis, K. A., & Ladle, R. J. (2008). A general dynamic theory of oceanic island biogeography. Journal of Biogeography, 35(6), 977–994. https://doi.org/10.1111/j.1365-2699.2008.01892.x

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3. 

   Version published to 10.1101/2024.10.07.616413 on bioRxiv

   Oct 8, 2024