Components of Pollen Limitation in Relation to Reproductive Success in Small Populations of Big Bluestem (Andropogon gerardii)
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Abstract
Reduced population size and plant density in fragmented habitats can limit fecundity due to inadequate pollination; however, the magnitude of pollen limitation in wind-pollinated species and the contributions of pollen quality versus quantity are poorly known. Here I investigated limits to reproduction in fragmented populations of Andropogon gerardii by quantifying seed production and its relation to pollen quantity and quality. The number of seeds per floret declined significantly with both population size and local density. Contrary to prediction, local density and population size were not related to pollen load. The percentage of compatible pollen and the percentage of florets with more than one pollen tube reaching the base of the style increased with both measures of abundance, likely due to increased mate availability. However, measures of pollen quality were weak predictors of seed set. In conclusion, fragmentation may affect reproduction in wind pollinated species through reductions in population size and local plant density, which influence the quality of pollen available.the quality of pollen available.