Prior to my doctoral dissertation research, the basic biology of rare plant Polemonium vanbruntiae (Eastern Jacob's ladder) was unknown.  Because of this, conservation management policies for remaining populations of this globally threatened species were ineffective and uninformed.  

---

Mating system, pollen limitation, and offspring performance
In 2004-2005, I conducted a series of hand-pollination experiments in both the lab and the field to determine the mating system and the extent of pollen limitation for P. vanbruntiae.  Populations are not limited by pollen probably because of this species ability to self-fertilize (Hill et al 2008).  I determined that P. vanbruntiae is self-compatible, but selfing reduces offspring performance.  I also found that hybrid offspring resulting from crosses between distant sites exhibit hybrid vigor (heterosis) compared to selfed offspring (Hill Bermingham and Brody 2011).


Although Polemonium vanbruntiae is self-compatible, its floral characteristics promote
outcrossing.  The stamens become functionally mature prior to maturation of the pistil, and as the
corolla opens, the unreceptive stigma surpasses the corolla by 5 – 7 mm.


                                                                                                         
After discovering that populations of P. vanbruntiae are not limited by pollen-receipt,
I tested whether plants can self-fertilize.  I bagged a series of treatment plants
with breatheable organdy fabric to exclude pollinators and hand-pollinated receptive stigmas with
within-plant self-pollen.  Contrary to our initial assumptions, P. vanbruntiae is self-compatible. 


I collected four years (2004-2007) of demographic data from 9 sites within the Green Mountain National Forest in central Vermont. With these data, I built matrix population models to project population growth rate and extinction risk. I determined that both white-tailed deer herbivory and habitat type (forest seep and wet meadow) significantly influence long-term population growth, but deer herbivory poses a far more significant threat to P. vanbruntiae populations (Hill Bermingham 2010).


I individually flagged and tagged P.vanbruntiae ramets and collected
annual data on the population vital rates (survival, growth, and reproduction).




Life cycle graph for Polemonium vanbruntiae.

Last modified March 16 2012 04:29 PM