Pollen Limitation Of Seed Production Research Articles

Causes and Consequences of Seasonal Variation in Pollen Limitation of Seed Production in Blandfordia grandiflora (Liliaceae)

Natural seed set was consistently pollen-limited for 5 yr in the perennial herb Blandfordia grandiflora. The extent of pollen limitation varied within seasons, depending on when individual plants lowered. In all years, percent seed set was greatest in January (36-41%) and least in March (12-14%). Seed set of hand-pollinated fruits did not differ within lowering seasons (46-52%), indicating that pollination factors caused natural seed set to vary. Variation in natural seed set was positively correlated with frequency of visits to lowers by nectarivorous birds, but not their abundance in the area. Bird abundance increased during the lowering season, but floral visits decreased. B. grandiflora lowers received about 2 visits in December, 3 in January, fewer than 1 in February and none in March. In February and March, B. grandiflora plants coflowered and competed for bird pollinators with Banksia serrata. In these months, birds preferentially foraged at Banksia serrata inflorescences which produced about 10-fold more nectar per 24 h. The consistently greater natural seed set in January suggests that optimizing selection would favour plants that lower in this month

Consumer Driven Pollen Limitation of Seed Production in Marsh Grasses

While flower predators can limit the sexual expression and seed production of salt marsh grasses, the relationship between these two effects of consumers has not been explored. At our study site, predation on Spartina patens, Spartina alterniflora, and Distichlis spicata was twice as high in 1985 (~70% ovule destruction) as in 1986 (~35% ovule destruction). In both years consumers destroyed flowers before maturity, reducing sexual expression, and particularly suppressed male sexual expression. Sexual suppression of males was much more pronounced in 1985 when flower predation was severe and the seed production of undamaged ovules was dramatically reduced. A number of lines of evidence suggest that predator limitation of male sexual expression and pollen supply contributed to low seed output in 1985. 1) Undamaged ovules of all three grasses protected from consumers but exposed to ambient windbome pollen set many more seeds in 1986 than in 1985, suggesting that pollen was more abundant in 1986; 2) Artificial pollinations revealed that marsh grasses are generally pollen-limited and that pollen limitation at our study site was more severe in 1985 than 1986; and 3) Caging stands of marsh grasses generally led to less predator damage, increased male densities and seed sets similar to those for hand-pollinated flowers. Our results support the hypothesis that flower predators can indirectly limit seed production by decreasing pollen availability.