Monitoring rare species: A case study with the Missouri bladderpod

Monitoring rare species and setting goals for restoration efforts are challenging when populations exhibit naturally high spatiotemporal variability.  The Missouri Bladderpod, Lesquerella filiformis, is a federally threatened winter annual that exemplifies such a restoration challenge.  Known only from a few counties in Missouri and Arkansas, this species occurs in clusters and exhibits dramatic population fluctuations among years.  Using computer simulations, we evaluated five different sampling approaches, including three adaptive designs, and compared these to a comprehensive survey based on abundance class estimates.  Overall, simulations revealed relatively small differences in sampling efficiencies among the designs evaluated, and demonstrated that sampling fraction was the most important factor that determined the precision of parameter estimates.  A comprehensive survey approach based on abundance class estimates resulted in similar to lower ranges of uncertainty associated with point estimates of population parameters, and produced spatially explicit information for the entire population.  Such information is valuable in elucidating changes in the spatial distribution of this population over time, and in evaluating the success of restoration efforts.  For example, cedar tree encroachment is thought to be an important factor in the decline of this species, and cedars are common at the study site.  Removal of cedars resulted in significant increases in L. filiformis densities.  Such a spatially explicit survey approach may be useful for the monitoring and restoration of other rare species.