Plant architecture directly and indirectly influences the abundance and diversity of arthropod predators and parasitoids

Background/Question/Methods

Intraspecific variation in plant traits is an important determinant of herbivore community composition, but the extent to which genetically-based plant traits have extended consequences on upper trophic levels is poorly understood.  Plants are often assumed to indirectly influence the abundance and diversity of upper trophic levels via herbivore community composition.  However, plant architecture may also directly influence the community composition of predators and parasitoids.  We examined how genetic variation in the willow, Salix hookeriana, directly and indirectly influences arthropod predator/parasitoid abundance and diversity.  Using a three-year-old common garden of the willow, Salix hookeriana, we photographed five replicate trees of 27 unique genotypes and quantified plant architecture using ImageJ.  We also vacuum-sampled 12 replicate trees of each genotype to determine arthropod community composition.  

Results/Conclusions

We found that willow genotype explained a significant amount of variation in plant architecture.  Furthermore, willow architecture had both direct and indirect consequences on predator/parasitoid abundance and diversity.  Our results highlight the fact that genetically-based variation in plant architecture may shift trophic structure in arthropod communities by directly influencing the abundance and diversity of upper trophic levels.