Roles of substrate, herbivory and competition in the generation of edaphic endemics: Experimental and historical approaches

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Ecological specialization, the process by which species adapt to a certain environment, has been central to understanding two important drivers of biodiversity: speciation (the evolution of new species) and extinction. Edaphic specialists, or species that only occur on particular soil types, contribute greatly to overall biodiversity. In California, serpentine soil outcrops (with high concentrations of heavy metals and low concentrations of essential plant nutrients) make up only 1% of the land but contain 14% (312 taxa) of the state's plant taxa. Adaptation to stressful substrates explains why plant species are found on these substrates, but does not explain why such species are restricted to them. One hypothesis suggests that adaptation to odd substrates decreases the ability to live on more typical substrates, but many edaphic specialists can grow on common soils when planted. Interactions with other species may thus be preventing edaphic specialists from colonizing more common soil habitats. The goal of the proposed work is to evaluate whether combined selection from soil components, herbivores and plant competitors has generated species limited to stressful substrates. Soil properties, growth on different substrates, and interactions with herbivores and plant competitors will be measured for the species in the genus Streptanthus, members of the mustard family. The evolutionary relationships among the species will be accounted for in the analyses to gain insight into past speciation events and their relationship with adaptation to serpentine soils. Several species of Streptanthus are listed as rare or endangered. A website will be created with information on soils and all stages in the life of these plant species (seeds through fruits). Such information will be useful for land managers in surveying populations of these plants. Some of these soil specialists have unique properties, like the ability to hyperaccumulate metals in their leaves, and have been used to reclaim metal-contaminated soils and for phytomining, thus this research will better inform such bioremediation efforts. Undergraduate, graduate students and technicians will be trained.