Host specificity of herbivorous insects promotes negative species–genetic diversity relationship

Although genetic diversity and species diversity in a community often
covary, the direction and strength of the covariation vary. However, this
variation in the relationship of these two diversities is poorly
understood. Here we investigated the role of host-specific herbivores in
generating species–genetic diversity relationship in plant communities. We
quantified host specificity for Fagaceae plants–acorn weevil bipartite
networks in a subtropical forest and modeled the effect of weevil
herbivory on the relationship. The results showed a consistently negative
relationship between Fagaceae species diversity and the genetic diversity
of the dominant species, Lithocarpus glaber. Our analysis showed this
negative relationship arose from a positive effect of weevil
host-specificity on Fagaceae plant richness on the one hand and the
negative effect of weevil host-specificity on the genetic diversity of L.
glaber on the other hand. This latter negative effect was possibly due to
differentiated selection of weevils on different genotypes of L. glaber.
Our study highlights the importance of considering trophic interactions
and herbivore host-specificity in explaining the species–genetic diversity
relationship.