Ecological Niche Differentiation of the Adiantum pedatum complex in the Green Mountains

How do substrate preference and other ecological factors impact the distribution and interaction of closely related species? I pursued answers to this question through study of the Adiantum pedatum complex, a clade of maidenhair ferns that exhibit a complex distribution pattern in northeastern North America directly tied to the geological chemistry of the region. Whereas A. pedatum is widely distributed in calcium-rich woodlands, A. aleuticum and A. viridimontanum are both restricted to serpentine-influenced substrates in northern VT and southern Quebec. A. viridimontanum, though a serpentine endemic, is a tetraploid hybrid lineage derived from a sterile hybrid between the maidenhair ferns A. aleuticum and A. pedatum, which are diploid. This reticulate evolution, uniting ecologically disparate ancestors, leads to the hypothesis that the two serpentine maidenhair ferns are ecologically isolated from one another as a result of inherent hybrid ecological intermediacy, competitive exclusion due to interspecific competition, or a combination of the two. To determine if the ecological niches of A. aleuticum and A. viridimontanum are differentiated from one another, multiple populations of all three species of maidenhair ferns were located in 10 field sites across Vermont. Their ecological niches were characterized in terms of light availability, topography, soil properties, and natural community type. Soil samples were submitted to the UVM Soil Lab for detailed analysis and flow cytometry was used to verify field identifications. Ecological data were analyzed using principal components analysis and discriminant function analysis, in order to identity the factors most important in distinguishing the ecological niches of the three maidenhairs. Initial results suggest that the ecological niche of the hybrid maidenhair fern is intermediate between those of its progenitors, supporting the hypothesis that the niches of the two serpentine maidenhair ferns are ecologically differentiated from one another. Introduction Plant distribution results from a complex interplay between the abiotic and biotic ecological factors that characterize the landscape in which a plant lineage evolves. The presence of a particular plant in a given location reflects the convergence of ecological conditions in which the plant is physiologically able to live. The range of ecological conditions that different plants are able to inhabit varies widely. Some plants are generalists, able to grow in a wide range of habitats, whereas other plants are specialists, restricted to a narrow range of habitats. These habitats vary in abiotic conditions such as temperature, precipitation, topography, light availability, and bedrock and soil type. Biotic variables also define the habitat in which plants grow; these variables include relations with mycorrhizal fungi and other soil microbes, as well as with animals that act as pollinators, seed dispersers, and herbivores. Additionally, plants interact with one another, acting as hosts, competitors, parasites, and facilitators. Species distribution is also constrained by the different reproductive biologies of the major lineages of land plants. The distribution of flowering plants is influenced to some degree by their relations with pollinators and seed dispersers, because the ranges of the co-