Plant reproduction is often pollen-limited. Underlying causes of pollen limitation could include a lack of available mates or competition for mates. Mating potential between individuals increases with temporal synchrony of mating behavior and decreases with spatial proximity. If pollen-limitation occurs due to lack of conspecific mates, plants with higher mating potential should have higher fitness. We conducted an observational study on three tallgrass prairie perennials examining the relationship between mating potential, prescribed fire, and 4 components of reproductive fitness: stems, flowers, fruits, and seeds. Prairie fire is thought to stimulate flowering and in two of the species, fire is associated with higher flowering synchrony and reproductive success. Because all three species flower determinately, mating potential and fire may differentially impact components of reproductive fitness. We predict that fire influences stem, flower, and fruit counts which are determined before flowering begins, while mating potential influences seed production. Using an Aster modeling approach with six years of data for 319 Echinacea angustifolia plants and 1 year of data for 75 Liatris aspera and 79 Solidago speciosa plants, we examine how multiple components of reproductive fitness are related fire and the mating scene, and report the degree of pollen limitation for all species.
Results/Conclusions
Reproduction in all three species was pollen-limited when plants receiving hand pollination were compared with open pollinated plants (p < 0.05 for all species). In Echinacea, individuals in burned areas had on average 93% higher mating potential, 36% higher synchrony and nearly double the seed set. In Echinacea, burns and synchrony but not mating potential are associated with the number of flowering heads. In Liatris, seed production was doubled for individuals that experienced fire, and increased with mating potential. In contrast to Echinacea, Liatris stem and head counts varied with the mating scene and fire. In Solidago, we found that fire had no relationship with seed set. Solidago individuals with lower mating potential and high flowering synchrony had high reproductive fitness. This suggests Solidago has higher reproductive success when there is less local competition with mates. Stem count but not head count varied with mating potential and synchrony in Solidago. Our results suggest components of reproductive fitness differentially relate to mating potential and fire in tallgrass prairie forbs. Species specific responses yield insight into potential mechanisms driving pollen limitation. For Echinacea and Liatris, mate limitation may drive pollen limitation, while in Solidago, competition for mates may be the cause.