Drivers of plant local adaptation and the consequences for multi-trophic communities in a rapidly changing world

As global change disrupts historical patterns of variation in the abiotic and biotic environment, there is an urgent need to not only investigate the ecological impacts of these complex changes, but how these novel environments will affect the evolutionary trajectory of local populations. Local adaptation—the process by which populations within a species adapt to local abiotic and biotic conditions—bridges past evolutionary processes with contemporary ecological dynamics, and can serve as a vital tool for predicting how ecological communities might adapt to rapid global change. However, a gap remains in how local adaptation is shaped by the joint stressors of the abiotic and biotic environments, and climate change will impact both plants and their associated biotic communities. To fill this gap, my dissertation investigates (1) the roles of aridity, soil, and herbivore pressure in shaping plant local adaptation and (2) climate change impacts on plants and their associated biotic communities. Artemisia californica is a foundational shrub species of the critically endangered Coastal Sage Scrub habitat that occupies a broad range of environmental conditions and serves as a critical food source for higher-trophic levels. I leverage a series of common garden experiments comprised of populations of A. californica sourced along California’s coast to generate ecotype by environment mixtures. I found strong evidence of plant adaptation to local aridity and soil conditions, such that plants performed worse when growing in climatic and edaphic environments that differed from their home environments. Moreover, I report evidence that plant adaptation to latitudinal variation in resource availability influenced genetic variation in multi-variate defense strategies, with plants from high- vs low-resource environments being less resistant but more tolerant to vertebrate herbivory. With respect climate change impacts, increases in mean aridity had stronger impacts on populations adapted to dry (vs wet) soils. Regarding drought, southern (arid) populations were more resilient to extreme drought compared to norther (mesic) populations, allowing southern populations support greater lifetime arthropod abundance. Altogether, these results forecast that increases in mean aridity will favor the northward migration of populations or that populations will adapt a more “southerly” defense phenotype. However, there might be heterogenous impacts of climate change, with northern populations being more vulnerable to extreme drought and populations adapted to dry soils more vulnerable to increasing mean aridity, and these reductions on plant performance can ultimately reduce arthropod abundance and alter associated arthropod community composition