Arthropod community similarity in clonal stands of aspen: A test of the genetic similarity rule

Understanding the factors that affect community composition is essential for community ecology. The geneticsimilarity rule (GSR) identifies 3 variables (host geneticcomposition, phytochemistry, and the environment) that could affect community composition. Few studies have determined the relative influence of these variables on community composition. Using path analysis, we found that arthropodcommunity similarity was better explained by geographic (56%) and environmental (32%) distance than geneticdistance in clonal aspen (Populus tremuloides). Comparing our data with data from similar studies of poplars (P. fremontii and P. fremontii × P. angustifolia hybrids), we found that hybrid poplar stands had higher levels of geneticand arthropoddiversity than did clonal aspen stands. We found a significant relationship between geneticand arthropoddiversity only in hybrid stands and across Populus systems. Our findings agree with the GSR expectations that the importance of the geneticcomposition of the host in structuring communitiesdepends in part on the amount of geneticvariation present in the study system. This is relevant for management and restoration strategies of geographically restricted species and of disjunct populations of otherwise widespread species, as these tend to have lower effective population sizesand reduced levels of geneticdiversity.