Rare plant species are at a disadvantage when both herbivory and pollination interactions are considered in an alpine meadow

1. Rare plant species often suffer less damage than common species because
of positive density-dependent herbivory, and it has been suggested that
this “rare species advantage” fosters plant species coexistence. However,
it is unknown whether rare species have an advantage when pollination
interactions are also considered. 2. We hypothesized that a “positive
density-dependent pollination success” across plant species would result
in common plants experiencing higher seed set rates compared to rare
species, and that positive density-dependent effects would negate or even
override the positive density dependent damage due to herbivory resulting
in higher seed loss rates in common plant species. 3. We tested this
hypothesis by concurrently examining a plant-predispersal seed predator
system and a plant-pollinator system for 24 Asteraceae species growing in
an alpine meadow community (Sichuan Province, China). Having previously
reported a positive density-dependent effect on seed loss rates due to
seed predators, we here focus on the density-dependent effects on
pollination success by investigating pollinator species richness,
visitation frequencies, and seed set rates for each plant species. We also
estimated the seed output rate of each plant species as the product of
seed set rate and the rate of surviving seeds (i.e., 1 – the seed loss
rate). 4. Consistent with our hypothesis, a positive density-dependent
effect was observed for pollinator species richness, visitation
frequencies, and seed set rates across plant species. Moreover, the
positive effect overrode the negative density-dependent effect of
herbivores on seed production, such that common species tended to have a
higher seed output rate than rare species (i.e., we observed a “rare
species disadvantage”). 5. These results indicate that the low seed output
rate of rare species might result from a pollination limitation, and that
both mutualistic and antagonistic interactions should be examined
simultaneously to fully understand plant species coexistence in local
communities. 23-Feb-2021