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

Abstract

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.

Insect root feeders incur negative density‐dependent damage across plant species in an alpine meadow

“…However, our data reveal negative density‐dependent damage resulting from root feeders across plant species due to the mismatch of the vertical distribution of roots and root feeders, but not the feeding preferences of root feeders. This is similar to the phenomenology of mutualistic interactions, where pollinators facilitate reproductive success among common species but not among rare species (Evans et al, 2017; Xi et al, 2021). It is possible that such negative root feeder density‐dependent damage may lead to species loss and changes in community assembly.…”

“…One recent important finding is that density‐dependent plant damage depends on interaction types, for example, seed production is positively density dependent for predispersal seed predator interactions in an alpine meadow (Xi et al, 2021), whereas foliar damage of seedlings peaks at intermediate tree density, possibly because of predation satiation at high tree density in a tropical forest (Bachelot et al, 2016). Because plant density effects on plant fitness are collectively determined by different types of interactions, the CCT does not necessarily hold true for every different type of interaction.…”

Eco‐evolutionary causes and consequences of rarity in plants: a meta‐analysis

“…Many invasive species inhabit disturbed ecosystems (Catford et al ., 2012; Jauni et al ., 2015), and similarities in those systems, such as increased resource availability (Davis et al ., 2000), could favor traits generally associated with invasiveness, including rapid growth rates, high fecundity and highly efficient seed dispersal (Hamilton et al ., 2005; Pyšek & Richardson, 2007; van Kleunen et al ., 2010). By contrast, species can be rare for many reasons, including their evolutionary history (Hodgson, 1986; Jetz et al ., 2004), specialization to rare habitats (Miller‐Struttmann, 2013), biotic interactions such as competition or herbivory (Speed & Austrheim, 2017; Zhang & van Kleunen, 2019; Xi et al ., 2021), and/or anthropogenic factors including habitat loss and climate change (Lavergne et al ., 2005; Van Calster et al ., 2008; Harrison et al ., 2019). The myriad reasons underlying rarity could explain our findings of limited phenotypic differences.…”