Riparian ecosystems in the southwestern U.S. are currently in decline due to drought from increased warming, urban development and exotic species invasion. In this NSF Macrosystems project, we evaluate how climate influences landscape genetic connectivity in a widespread foundation species (Populus fremontii, Fremont cottonwood) and how this, in turn, affects connectivity in dependent arthropod communities across the species range. Using three experimental common gardens distributed across a climate gradient, we assess how simulated climate change impacts Fremont cottonwood performance and survival. Using genome-wide SNP markers we have generated a “genetic connectivity” map for Fremont cottonwood and examined gene flow in the context of environmental variables that either impede or facilitate the movement of genes across the landscape. Using this information in the context of a reciprocal causal modeling framework, we test a battery of competing hypotheses that describe how landscape genetic connectivity, in turn, influences dependent community connectivity.
Results/Conclusions
Our results indicate that: 1) Fremont cottonwood responds to environmental variation across a climate gradient, exhibiting significant G, E, and GxE effects; 2) Genotypes from both low, mid and high elevation gardens show significant phenotypic plasticity in important functional traits that may enhance adaptation to a warming climate; 3) Landscape genetic connectivity in Fremont cottonwood is broadly structured into three main ecoregions comprising the Utah High Plateau, the Sonoran Desert and the California Central Valley. These ecoregions are accompanied by strong correlations to several environmental variables, further suggesting adaptation to large-scale environmental patterns; 4) At a finer scale within an ecoregion, individual populations are adapted to their local environment, as reflected in higher survival and growth; 5) Fluctuating leaf asymmetry and leaf thermal regulation is associated with a mismatch in plant traits and the local environment and is correlated with reduced performance, effectively functioning as a biomarker for evaluating the limits of assisted migration; 6) Arthropod species richness and abundance are structured according to different ecoregions, as defined by Fremont cottonwood. Overall, our results provide alternative genetics-based management strategies to conserve foundation species and their dependent communities in the context of a changing climate.