Abstract
Mating activities change within a season in many animal and plant populations. In plants, selection towards early flowering is commonly observed. Pollinator-mediated selection is hypothesized to be a pervasive evolutionary force acting directionally on flowering time. However, pollinator-mediated mechanisms have rarely been tested in realistic field conditions, especially in perennial plants visited by a diversity of generalist insect pollinators. We examined pollinator visitation in eight Echinacea angustifolia populations in western Minnesota, USA, to gauge the potential for pollinator-mediated selection. Echinacea is a common prairie perennial that persists in isolated remnant populations. Echinacea is self-incompatible and is pollinated by a diversity of generalist solitary bees. A previous study found that early flowering Echinacea plants have higher seed set and their reproduction is less pollen-limited than late flowering plants. Twelve times throughout a flowering season, we quantified pollinator visitation rates and pollinator community composition. In three sites, we also estimated the quality of pollinator visits by examining the composition of pollinators’ pollen loads brought to Echinacea plants. We found that three aspects of pollination dramatically decreased over the course of the flowering season. 1) Pollinators visited early flowering plants more frequently than late flowering plants. 2) The pollinator community was also less diverse late in the flowering season and became dominated by a single species of small bee, Augochlorella aurata. 3) Pollinators visiting Echinacea late in the season carried proportionally less conspecific pollen compared to pollinators visiting Echinacea early in the flowering season. Understanding within-season dynamics of pollination helps predict the prevalence of inbreeding, phenological assortative mating, and reproductive failure, especially in fragmented plant populations.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1657-1669 |
| Number of pages | 13 |
| Journal | Oikos |
| Volume | 127 |
| Issue number | 11 |
| DOIs | |
| State | Published - Nov 2018 |
Funding
Acknowledgments – We thank members of Team Echinacea 2016 for observing pollinators and monitoring flowering phenology. In addition, we thank L. C. Leventhal for assisting with catching pollinators, G. Kiefer for organizing the flowering phenology data, D. Sponsler for advice on pollen grain identification, and L. C. Leventhal, A. Jacobs and A. Fairbanks-Mahnke for organizing and watching the pollinator visitation videos. Thank you to The Nature Conservancy, U.S. Fish & Wildlife Service, Minnesota D.N.R., and private land owners for access to the sites. We thank E. J. Austen and J. Ogilvie for helpful comments on this manuscript. Funding – This research was funded through National Science Foundation awards 1557075, 1555997, 1355187 and 1052165 to SW and a supplemental ROA award to SW and JLI. Additional funding was provided through The College of Wooster’s Wilson and Copeland Awards. Author contributions – JLI and LJP contributed equally to this work. JLI, LJP and SW designed the study. All authors contributed to the field and laboratory work. SWN, AW and SW analyzed the data and prepared figures and tables. JLI and LJP wrote the first draft of the manuscript. All authors contributed significantly to revisions of the manuscript and gave final approval for publication.
Keywords
- Echinacea angustifolia
- flowering phenology
- fragmentation
- mate limitation
- plant–pollinator interactions
- pollinator-mediated mechanisms
- temporal mating patterns
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics