With the support of an NSF Macrosystems grant, we addressed the hypothesis that genetic differences among plants from different sites along a distance/elevation gradient would influence the communities they acquired in a common garden. In other words, “If you build it will they come?” Answers to this hypothesis are especially important when considering the community consequences of assisted migration along distance/elevation and latitudinal gradients. We surveyed the arthropod communities occurring on the foundation riparian tree species Populus angustifolia along a distance/elevation gradient of 90km and 530m, respectively and in a common garden where trees from along the gradient were randomly planted 20-22 years prior to our study.
Results/Conclusions
Three major patterns were found; 1) Arthropod community composition changed significantly along the gradient. Trees sourced from the lower elevation nearest to the common garden supported up to 58% greater arthropod abundance and 26% greater species richness than more distant, high elevation trees. 2) Trees grown in a common garden sourced from the same locations along the gradient, support arthropod communities more similar to their corresponding wild trees, but the similarity declines with distance and elevation. 3) Leaf area, a trait under genetic control that decreases at higher elevations, is correlated with differences in arthropod species richness and abundance. Over this experimental gradient, our results argue that genetic differences in functional traits are strong drivers of arthropod community composition that depending on transfer distance, do support communities from their source site rather than just supporting the local community. We also show that variation in a plant trait (leaf area) is maintained and has similar effects at the community level while controlling for environment. These results are an important demonstration of how genetically based plant traits vary across natural gradients and have community level effects that are maintained, in part, when they are moved to a new site.