Many mechanisms influence plant species distributions, including biotic and abiotic factors, and each differentially impacts the range and conservation status of species. However, many of the factors shown to be important, specifically interspecific interactions, are not well understood. Pollinator interactions are assumed to be important for the reproductive success and persistence of native plant species, but little is known about the pollination biology of endemic glade species. The frequently observed inverse correlation between growth and reproduction could be exacerbated in predictably stressful environments. Field and herbarium measurements suggest that glade endemics have traits (i.e., longer floral spur length and tube depth) associated with more specialized pollination systems and more restricted reproduction, specifically lower relative reproductive potential, than their widespread congeners. Consequently, the proposed objectives of this study are to elucidate the degree of specialization, overlap in the pollination biology, and stress adaptation of these glade endemics when compared with their widespread congeners. I conducted pollinator observations, pollen load analyses, pollen limitation experiments, and breeding system experiments of three glade endemics and their widespread congeners. I assessed the relationship between reproduction and stress adaptation with field measurements of multiple reproductive and vegetative traits along a natural gradient of environmental stress.

Results/Conclusions

I found that glade endemics have more specialized pollination systems and traits associated with adaptation to stressful environments. Glade endemics are less negatively impacted by stress along a natural gradient. Preliminary data suggest some overlap in the pollination biology of endemic and widespread species, which could result in competition for pollinator services. These results suggest a trade-off between reproduction and stress adaptation that may contribute to the limited biogeographical extent of these endemic glade species. These pollination interactions should be incorporated into ecological niche models used to predict species responses to climate change and into conservation strategies for glade endemics.