Providing a quantitative assessment of threatened plant populations, that holds for varying management scenarios, has become an essential part of conservation planning. Here, renowned plant ecologists provide information on: major threats to plants, when and where to conduct a plant viability assessment (PVA), what type of PVA to conduct, what alternative options to PVA are available, what information is required for which kind of viability assessment, what attributes of the population in question should be considered, and what the limits of the PVA would be. As such, this volume can be used as a training tool for the environmental manager or a teaching aid for reviewing the current state of knowledge on plant population viability.
This important work features discussions on the distribution and significance of genetic variation, management and evaluation of rare plant germplasm, and conservation strategies for genetic diversity.
As human populations and the resources required to support societies continue to grow, an increasing number of plant and animal species around the world are facing extinction. Given limited time, space, and money, how do we decide which management actions will be most effective to avert extinctions? In this book, many of the world's leading conservation and population biologists evaluate what has become a key tool in estimating extinction risk and evaluating potential recovery strategies—population viability analysis, or PVA. PVA integrates data on the life history, demography, and genetics of a species with information on environmental variability, using computer models ranging from simple measures of population growth rate to complex spatial simulations, to predict whether a given population will remain viable (i.e., not go extinct) under various management options. A synthetic and objective overview of the latest theoretical and methodological advances, Population Viability Analysis will be crucial reading for conservationists, land managers, and policy makers.
Demographic information was collected from the only known, naturally-occurring population of Hazardia orcuttii in the United States located at the Manchester Conservation Area at Lux Canyon, Encinitas, California. Six surveys were performed between January 2004 and July 2005. Four surveys measured plant size (diameter and height) from all Hazardia within thirteen 12.56 m2 plots. The height data were used to create four size classes (SCI =less than 0.35 m; SC2 = 0.351-0.55 m; SC3 = 0.551-0.79 m; and SC4 =greater than 0.79 m) for a population viability analysis (PYA). Two additional surveys, collecting the same measurements described above, were performed on 40 tagged plants, one plant within each SC at ten of the thirteen plots, in December 2004 and April 2005. Height measurements from the 40 tagged plants, along with seed production and viability data, were used to create a Leftkovitch stage class model. This model was used to run a PVA which simulated changes in the initial population size, the distribution of individuals within size classes, fertility, growth, herbivory, and increased survival probability by size class (SC). The PVA revealed that under current demographic conditions the existing population is not sustainable, with a finite rate of increase (A.) of 0.960 individuals per year. Manipulations of the model indicate that increases in fecundity ofSC3 and SC4 (F 3 = 2.455, F4 = 3.480); an increase in the graduation probability between SCI and SC2 (G1,2 = 0.170); and increases in the survival probabilities of SCI, SC3, or SC4 may increase the population's viability potential. Additional populations may also help to decrease the extinction risk for Hazardia. Key words: Hazardia orcuttii, population viability analysis, stage class model, rare plant, California, endemic