Differences in individual flowering time change pollen limitation and seed set in three montane wildflowers

Abstract

Premise: Changes to flowering time caused by climate change could affects plant fecundity, but studies that compare the individual-level responses of phenologically distinct, co-occurring species are lacking. We assessed how variation in floral phenology affects the fecundity of individuals from three montane species with different seasonal flowering times, including in snowmelt acceleration treatments to increase variability in phenology. Methods: We collected floral phenology and seed set data for individuals of three montane plant species (Mertensia fusiformis, Delphinium nuttallianum, Potentilla pulcherrima). To examine the drivers of seed set, we measured conspecific floral density and conducted pollen limitation experiments to isolate pollination function. We advanced the phenology of plant communities in a controlled large-scale snowmelt acceleration experiment. Results: Differences in individual phenology relative to the rest of the population affected fecundity in our focal species, but effects were species-specific. For our earlyseason species, individuals that bloomed later than the population peak bloom had increased fecundity, while for our midseason species, simply blooming before or after the population peak increased individual fecundity. For our late-season species, blooming earlier than the population peak increased fecundity. The early and midseason species were pollen-limited, and conspecific density affected seed set only for our early-season species. Conclusions: Our study shows that variation in individual phenology affects fecundity in three phenologically distinct montane species, and that pollen limitation may be more influential than conspecific density. Our results suggest that individuallevel changes in phenology are important to consider for understanding plant reproductive success.

Phylogenetic diversity of flowering plants declines throughout the growing season across a subalpine elevational gradient

“…However, we found that abundance increased steadily over our data collection period (Supplementary material Fig. S2), which indicates that pollinators may not be more limiting over time and is consistent with prior findings [72,73].…”

“…Previous work has shown that pollen and pollinator limitation is often species-specific and/or context-dependent in RMBL plant communities [72,74,75], which suggests that the impact of co-flowering facilitation likely also depends on the context and individual species. Schiffer and colleagues (2023) found that early and middle-season species had higher fitness when they flowered separately from population peaks [72]. However, their late-season species, Potentilla pulcherrima , had the highest fitness when it flowered at its population peak.…”

Plant Species’ Capacity for Range Shifts at the Habitat and Geographic Scales: A Trade-Off-Based Framework

“…Pollination limitation, in which plants produce more ovules than are ultimately fertilized, can limit seed production, reducing colonization opportunities and wasting reproductive effort [ 172 , 173 ]. Plant phenological shifts related to climate change (e.g., early or delayed flowering) may increase or decrease individual fecundity [ 174 , 175 ], suggesting strong variation in seed production could occur across a species’ geographic range, which could enhance or reduce the colonization ability of specific populations. For example, the fecundity in eastern North American forests was shown to be highest towards southern edges of species’ distributions, limiting northward spread, whereas the ample fecundity and higher recruitment in western forests is facilitating tree species’ migration to higher latitudes [ 19 ].…”