The wide diversity of species found in ecological communities provides numerous ecosystem services to humankind. Yet scientists are only beginning to understand what factors maintain the diversity seen in plant communities. What keeps the fastest growing, most competitive plant from driving other species extinct? For a century, ecologists answered this question with "niche differences", where plant species differ in key ways that allow them to minimize competition. For example, different plants may take up water from different soil depths. Recently however, ecologists have come to recognize that species need not differ to coexist. In fact, identical species co-occur for long periods of time in mathematical models, raising an alternative hypothesis for coexistence. The principle investigators of this proposal have developed a novel framework for determining whether species differences underlie the biodiversity seen in plant communities. This framework relies on the fact that 'niche differences' give species advantages when they drop to low density, decreasing their probability of extinction and increasing diversity. The investigators will assess whether California annual plant species living on serpentine soils experience such advantages when rare. In so doing, they assess the role that niche differences play in maintaining diversity in this unique and diverse habitat. The broader impacts include the training of graduate students at two universities, the development of ecological teaching modules, outreach to students from underprivileged schools, and increased understanding of a habitat of conservation concern. The research will be among the first experimental studies addressing the role that species differences play in controlling biodiversity.
