Background/Question/Methods   Patterns of evolutionary history in plant communities can affect productivity and ecosystem function but it is unknown what response arthropod assemblages will have. We compared diversity and abundance of herbivorous and predaceous arthropods with the phylogenetic diversity of plant communities from which they were collected, using a large dataset from a long-term ecological experiment in Cedar Creek Ecosystem Science Reserve. Additionally, we compared the explanatory power of phylogenetic diversity with a large number of other factors, including species richness, aboveground biomass, and a suite of plant traits, using Akaike's AIC model selection methods.

Results/Conclusions   We found that phylogenetic diversity was a strong positive predictor of species richness for both herbivorous and predaceous arthropods, as well as the abundance of predaceous arthropods (but not the abundance of herbivorous arthropods). We also found a strong interaction between plant phylogenetic diversity and plant species richness, which showed that arthropod diversity was most positively impacted by plant species richness when phylogenetic diversity of plants was high. When phylogenetic diversity was low, species richness had little impact on arthropods. Consistently, phylogenetic diversity explained more variation in arthropods than other factors. Plant communities with high phylogenetic diversity may support high diversity of arthopods for several reasons, including increased trait variation, which could lead to more complex habitat structure. Also, the presence of more lineages may allow for the recruitment of more lineage-specific specialists. These results show that a much greater understanding of assemblages at higher trophic levels can be achieved by incorporating information about the evolutionary history represented in plant communities. Specifically, our results suggest that the adding of more species to plant communities will not necessarily increase diversity at higher trophic levels unless those species add considerable evolutionary history to the community as well.