Influence of pollination mode on FST
We found that pollination mode plays a key role in population differentiation, contrary to the findings of the latest review of FST and species traits in seed plants (Duminil et al., 2007). Specifically, species pollinated by small insects have significantly higher FST than those with other pollination modes. This pattern is likely due to reduced gene flow among plant populations. In fact, small insects have a lower pollen carry-over capacity than bumblebees and vertebrates (Dick et al., 2008; Rhodes, Fant, & Skogen, 2017), and studies of pollinator movement show that euglossine bees, hawkmoths, and bats can all travel long distances, even across fragmented habitats (Brunet, Larson-Rabin, & Stewart, 2012; Finger, Kaiser-Bunbury, Kettle, Valentin, & Ghazoul, 2014; Janzen, 1971; López-Uribe, Oi, & Del Lama, 2008; McCulloch et al., 2013; Skogen, Overson, Hilpman, & Fant, 2019). Our results show that wind, large insects, and vertebrates have homogenizing effects on plant FST, which are statistically indistinguishable. Taken together, these patterns suggest that plants pollinated by small insects might be more sensitive to habitat fragmentation; the inability of these pollinators to connect distant fragments may decrease genetic diversity within populations, and along with it the ability to adapt in response to anthropogenic change.
One important caveat is that the limited information on pollination systems for many species necessitated a relatively coarse-grained division of pollination mode into broad taxonomic groups. This approach overlooks potential behavioral differences within these groups. For instance, within the vertebrate pollination category, territorial hummingbirds likely move pollen much shorter distances than trap-lining hummingbirds (Betts, Hadley, & Kress, 2015; Ohashi & Thomson, 2009), and bats may carry pollen more efficiently (Muchhala & Thomson, 2010) and to longer distances than hummingbirds (Lemke, 1984, 1985; Tello-Ramos, Hurly, & Healy, 2015).