| Abstract |
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Flowering phenology is central to plant reproductive success and can relate to morphological traits such as size and quality of flowers, but phenology–trait associations of flowers remain unclear. Phenology–trait associations can vary within and among species, especially across climate gradients, due to allocational trade-offs in response to selective pressures from abiotic stress and/or biotic factors such as pollinator availability. It is unknown whether floral morphology and phenology experience coordinated selection across climate gradients or vary independently.
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Understanding the drivers of trait variation and its implications for floral phenology may be especially relevant in mountains where climate and abiotic gradients change sharply with elevation. At higher elevations, increasing cold and aridity may favour higher quality, stress-tolerant flowers that withstand harsher conditions better than cheaper flowers, but trade-off with size and showiness to pollinators. Relatively benign conditions at lower elevations may permit more flexible phenotypes and weaker association between trait and phenology by allowing species more leeway for flowering times compared with the short growing season at higher elevations.
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We examined trait–phenology associations within and among 250 herbaceous species in the Western Himalayas, spanning 2000–4500 m AMSL. Intraspecific variation in traits and phenology decreased from low to high elevation at the community scale, but species showed idiosyncratic responses. Trait–trait correlations indicated stronger selection and constraints on phenotypes and phenology at higher elevations. However, trait–phenology correlations were relatively weak throughout, suggesting independent selection on flower morphology vs. phenology.
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Overall, climate imposed strong selection on flower traits and regulated floral phenology, but without any strong or consistent associations between traits and phenology. It is likely that flower morphology responded to multiple abiotic and biotic drivers, within and across elevations, whereas phenology mainly responded to temperature and thaw. Our findings suggest that selection from ongoing warming will operate separately on floral morphology and phenology of alpine plant communities, and mechanisms and consequences should be evaluated using experiments.
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