Pollination of Echinacea angustifolia: Effects of Flowering Phenology and Spatial Isolation.

摘要

Elucidating patterns of pollination is vital to our understanding of native plant population persistence in ecosystems that have experienced severe destruction and habitat fragmentation, such as the North American tallgrass prairie. I quantified the effects of spatial isolation and flowering phenology on seed set in an experimental plot for three years. In all three years, later flowering plants set between 20-40% fewer seeds than early or peak flowering plants. Spatially isolated plants set significantly lower seed than plants in high density patches in two of the three years. I used microsatellite markers to assess effective pollen movement within an experimental plot and pollen immigration from outside the plot. Most (84%) of the plants in the plot sired at least one offspring of the 765 offspring that were assigned paternity. Significantly more pollinations occurred between near neighboring and synchronous plants than expected under random mating. There was also high pollen immigration (3-14%) from outside the experimental plot. Extensive fragmentation of the tallgrass prairie is predicted to limit pollen and seed dispersal. I characterized the genetic variation in 10 remnant populations. All remnants showed high diversity (gene diversity = 0.676-0.72), low inbreeding (FIS = -0.159-0.059), and low levels of differentiation (global FST = 0.043). However, smaller remnants had significantly higher pair-wise relatedness than larger remnants. Harvesting seed is central to many aspects of ex situ conservation. I examine how timing of seed collecting affects the quantity and quality of the seeds harvested. I found lower seed set in late harvested plants. Later harvested plants also had significantly lower germination and seedling survival. The overall neutral genetic diversity represented over harvest times was high. My studies provide the most detailed results to date regarding how pollination is influenced by both spatial isolation and flowering phenology. This research has conservation implications for both the population persistence of small isolated remnants and for seed harvest timing for ex situ conservation efforts.