Adaptation in serpentine and non-serpentine habitats: Using 150 field plots across a landscape to understand adaptation to the biotic and abiotic environment in two locally adapted ecotypes of a native plant, Collinsia sparsiflora

Within any particular species range, populations exist across different habitats where natural selection varies in space and time. Locally adapted ecotypes are expected to respond to predictably different attributes of the environment. We have documented local adaptation in Collinsia sparsiflora ecotypes from both serpentine and non-serpentine soils. However, while botanists and ecologists often define habitats or communities as serpentine or non-serpentine, we do not know the specific environmental attributes that improve (or reduce) plant performance within these habitats. Here we show that the ecotypes respond differently to competition as well as soil attributes. Plants from serpentine and non-serpentine ecotypes were grown in 100 field plots where soil and habitat data had been quantified. In addition, there were 50 plots where all aboveground biomass had been removed. Removing above-ground competitors resulted in much higher fitness in both ecotypes, however, serpentine ecotypes had a greater response, suggesting that the observed poor performance of serpentine plants in non-serpentine habitats could be related to competition. Survival to flowering was greater overall for serpentine plants, however, there was a negative relationship between survival to flowering and zinc as well as plot biomass. Furthermore, an ANCOVA showed variation in slopes between serpentine and non-serpentine plants for their response to both biomass as well as calcium in the soil (an important limiting nutrient in most serpentine soils). Our data show that there is adaptation to both the biotic and abiotic environment, and suggest a tradeoff where the serpentine ecotype shows greater abiotic tolerance but reduced competitive ability.