Seed dormancy is expected to provide ecological advantages by adjusting germination to the favorable growth period. However, many species produce nondormant seeds, particularly in wet tropical forests, a biogeographic pattern that is not well accounted for in current models. We hypothesized that the global distribution of dormant seeds derives from their adaptive value in predictably fluctuating (i.e. seasonal) environments. However, the advantage conferred by dormancy might ultimately depend on other seed attributes, particularly size. This general model was tested within a phylogenetically informed framework using a data set comprising > 216 000 world-wide observations of Fabaceae, spanning three orders of magnitude in seed size and including both dormant and nondormant seeds. Our results confirmed our hypothesis: nondormant seeds can only evolve in climates with long growing seasons and/or in lineages that produce larger seeds. Conversely, dormancy should be evolutionarily stable in temperate lineages with small seeds. When the favorable season is fleeting, seed dormancy is the only adaptive strategy. Based on these results, we predict that, within a given lineage, taxa producing larger, nondormant seeds will necessarily predominate in aseasonal environments, while plants bearing small, dormant seeds will be dominant under short growing seasons.
Bibliographical noteFunding Information:
This paper is the product of the working group ?Germination, trait coevolution and niche limits in changing environments? organized by Kathleen Donohue and R.R.d.C. and sponsored by the National Evolutionary Synthesis Center, National Science Foundation EF-0905606. R.R.d.C. was additionally funded by the European Commission (MC-IIF-2011-300026 ?TEE-OFF?) and the Talentia program (Junta de Andalucia/EC ? FP7 CFUND; grant agreement no. 267226, ?Bet-hedging, trade-offs and the evolution of seed dispersal and dormancy?). J.C-B. would like to thank the EEB Theory Group at the University of Minnesota, particularly Tanjona Ramiadantsoa, Allison Shaw and Xiaojing Wei, for feedback on the mathematical model.
© 2017 The Authors. New Phytologist © 2017 New Phytologist Trust
- discrete traits
- mixed models
- phylogenetic comparative methods
- physical dormancy
- seed bank
- seed germination
- seed predation