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We addressed the hypothesis that intraspecific genetic variation in plant traits from different sites along a distance/elevation gradient would influence the communities they support when grown at a new site. Answers to this hypothesis are important when considering the community consequences of assisted migration under climate change; i.e., if you build it will they come?. We surveyed arthropod communities occurring on the foundation riparian tree species Populus angustifolia along a distance/elevation gradient and in a common garden where trees from along the gradient were planted 20–22 years earlier. Three major patterns were found: 1) In the wild, arthropod community composition changed significantly. Trees at the lower elevation site 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, supported arthropod communities more similar to their corresponding wild trees, but the similarity declined with transfer distance and elevation. 3) Of five functional traits examined, leaf area, a trait under genetic control that decreases at higher elevations, is correlated with differences in arthropod species richness and abundance. Our results suggest that genetic differences in functional traits are stronger drivers of arthropod community composition than phenotypic plasticity of plant traits due to environmental factors. We also show that variation in leaf area is maintained and has similar effects at the community level while controlling for environment. These results demonstrate how genetically based traits vary across natural gradients and have community-level effects that are maintained, in part, when they are used in assisted migration. Furthermore, optimal transfer distances for plants suffering from climate change may not be the same as optimal transfer distances for their dependent communities. 

Genetic variation within a dominant riparian forest tree affects susceptibility to a leaf-galling aphid (Pemphigus betae), which induces phytochemical and structural changes in leaf tissue. Research Highlights: We show here that these changes to tree leaf tissue alter adjacent in-stream leaf litter decomposition rates and the aquatic macroinvertebrate community associated with litter in the stream for some Populus genotypes. Background and Objectives: Naturally occurring hybrid cottonwoods (Populus fremontii × Populus angustifolia) are differentially susceptible to aphid attack and vary in induced phytochemistry following attack. When leaves are galled by aphids, foliar tissue is altered structurally (through the formation of pea-sized gall structures) and phytochemically (through an increase in foliar condensed tannin concentrations). Materials and Methods: To examine the effect of aphid-galled leaves on forest stream processes, we collected both galled and un-galled leaves from five clones of three hybrid cottonwood genotypes in an experimental forest. We measured in-stream litter decomposition rates, aquatic fungal biomass and aquatic macroinvertebrate community composition. Results: Decomposition rates differed among genotypes and the galled litter treatments, with a 27% acceleration of decomposition rate for the galled litter of one genotype compared to its own un-galled litter and no differences between galled and un-galled litters for the other two genotypes. Genotype by foliar gall status interactions also occurred for measures of phytochemistry, indicating a prevalence of complex interactions. Similarly, we found variable responses in the macroinvertebrate community, where one genotype demonstrated community differences between galled and un-galled litter. Conclusions: These data suggest that plant genetics and terrestrial forest herbivory may be important in linking aquatic and terrestrial forest processes and suggest that examination of decomposition at finer scales (e.g., within species, hybrids and individuals) reveals important ecosystem patterns. 

Global change is widely altering environmental conditions which makes accurately predicting species range limits across natural landscapes critical for conservation and management decisions. If climate pressures along elevation gradients influence the distribution of phenotypic and genetic variation of plant functional traits, then such trait variation may be informative of the selective mechanisms and adaptations that help define climatic niche limits. Using extensive field surveys along 16 elevation transects and a large common garden experiment, we tested whether functional trait variation could predict the climatic niche of a widespread tree species (Populus angustifolia) with a double quantile regression approach. We show that intraspecific variation in plant size, growth, and leaf morphology corresponds with the species' total climate range and certain climatic limits related to temperature and moisture extremes. Moreover, we find evidence of genetic clines and phenotypic plasticity at environmental boundaries, which we use to create geographic predictions of trait variation and maximum values due to climatic constraints across the western US. Overall, our findings show the utility of double quantile regressions for connecting species distributions and climate gradients through trait‐based mechanisms. We highlight how new approaches like ours that incorporate genetic variation in functional traits and their response to climate gradients will lead to a better understanding of plant distributions as well as identifying populations anticipated to be maladapted to future environments.