Abstract
Since pollen usually travels limited distances in wind-pollinated plant species, plants growing at low density may become pollen limited. We examined how local pollen availability and population density affect reproductive success in two wind-pollinated, dioecious species, Thalictrum fendleri and Thalictrum dioicum. Distance to the nearest flowering male, the number of flowering males within 2 m, and flower number on those males served as measures of local pollen availability. Increased distance from pollen donors reduced seed set in the lowest-density population of each species, but seed set in high-density populations was not correlated with local pollen availability. For plants in high- and low-density populations at similar distances from pollen donors, this distance only affected seed set in low-density populations. To ensure that differences in resource availability were not causing spurious correlations between seed set and plant density, we constructed low-density artificial arrays in populations of T. dioicum. In these, seed set decreased rapidly with increases in distance from pollen donors. Despite these effects, the density of males in a population was not correlated with average seed set in T. dioicum, and hand pollination in the T. dioicum populations also failed to increase seed set over natural levels. These results suggest that pollen receipt only limits seed set on isolated plants within low- density populations of T. dioicum and T. fendleri.
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Acknowledgements
We thank Murray Clayton, Thomas Givnish, Thomas Sharkey, Linda Graham, and four anonymous reviewers for helpful comments and discussion on earlier drafts of this manuscript. Brian Anacker, Jeanne Sheahan, Timothy Lisko and Josh Ladwig provided assistance in the field. This study constitutes part of JS’s dissertation research at the University of Wisconsin-Madison, and is based upon work supported under a National Science Foundation Graduate Fellowship to JS and grants from the Beta Chapter of SDE-Graduate Women in Science and the J. J. Davis fund of the Botany Department at UW-Madison.
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Steven, J.C., Waller, D.M. Isolation affects reproductive success in low-density but not high-density populations of two wind-pollinated Thalictrum species. Plant Ecol 190, 131–141 (2007). https://doi.org/10.1007/s11258-006-9196-2
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DOI: https://doi.org/10.1007/s11258-006-9196-2