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).