Table 1. Equations used to quantify components of reproductive isolation.

Barrier	Equation for calculating RI
Prezygotic
Geographic	1 – (no. of counties in which the species co-occur/no. of counties in which the species occurs)
Phenology	1 – (no. of days in which both species are in flower at the same time/no. total flowering days for the species)
Pollinator assemblage	1 – (flower visits by shared pollinators/total number of flower visits)
Pollinator behavior	1 – (no. of flower visits by pollinators coming from the respective other species/total no. of flower visits)
Postzygotic
Pollen precedence	1 – (the ration of pollen tube length to the total length of the style from interspecific/the ration from intraspecific pollination)
Seed production	1 – (no. of seeds per interspecific/no. seeds per intraspecific pollination)
Seed germination	(1 – no. of germinated seeds resulting from interspecific pollination/no. germinated seeds resulting from intraspecific pollination)

Each RI value was generally varying from 0 to 1, with 0 representing no barrier to inter-specific gene flow and 1 representing a complete barrier.