Monday, August 6, 2007

PS 7-94: A quantitative method for the prediction and characterization of rarity in vascular plants of the southeastern US

Lee Anne Jacobs, University of North Carolina and Robert K. Peet, University of North Carolina.

To create a quantitative framework to define rarity, I used a multivariate ordination analysis for plant species of the southeastern United States to determine how species distributions are defined by abundance, habitat, and range.  I then extended the analysis in two ways.  First, I conducted a simulation to determine if the quantitative framework can detect species shifting between forms of rarity.  I systematically changed values for each measure (abundance, habitat, and range) for selected species, which revealed shifts between forms of rarity for those species as well as the direction of shift (decrease in range, or decrease in local abundance, for example) relative to other species.  Second, I used the quantitative framework in combination with trait data from the USDA PLANTS Database to identify the traits most commonly occurring in each form of rarity.  In addition, I compared species within each form of rarity to existing lists of state and federally threatened species to assess the ability of this approach to identify species of conservation concern. 

This analysis provides three significant contributions.  First, it provides a management tool that can be tailored to any group of organisms to identify species at greatest risk.  Second, it reveals how a species is changing, allowing design of more effective and biologically-based strategies for protection.  Third, the correlation of traits with rarity provides a more detailed understanding of why certain species tend to be rare, and will allow prediction of which species may be more likely to become rare in the future.