A population viability analysis of the Lassics lupine (Lupinus constancei)
Graduation Date
2012
Document Type
Thesis
Program
Other
Program
Thesis (M.S.)--Humboldt State University, Biology, 2012
Committee Chair Name
Erik S. Jules
Committee Chair Affiliation
HSU Faculty or Staff
Keywords
Granivory, Herbivory, Lassics lupine, Lupinus constancei, Small mammal, Humboldt State University -- Theses -- Biology, Extinction, Population viability analysis, Matrix model, Seed predation
Abstract
The Lassics lupine (Lupinus constancei T.W. Nelson J.P. Nelson) is a rare herb of limited distribution, with fewer than 400 reproductive individuals restricted to a single square kilometer in the Lassics Geological and Botanical Area of the Six Rivers National Forest, California, USA. In addition to the vulnerability resulting from its extremely small population size, the Lassics lupine faces heavy seed predation by small mammals and encroachment of surrounding plant communities into its preferred habitat. As a stop-gap measure to prevent population decline, managers began covering a large number of the reproductive plants with herbivory exclosures in 2003, but the population-level effects of seed predation and the effectiveness of this caging treatment were unknown. In this study, I used ten years of demographic monitoring data collected by the US Forest Service to build a stage-structured matrix model, project population growth, and estimate the probability of species extinction in the next 50 years. The model included vital rate estimates for each of three main sites, as well as vital rate correlations between and within sites and years. I used a one-way life table response experiment (LTRE) to quantify the effects of caging on the population growth rate. Finally, I used a regression LTRE to estimate the proportion of the population at each site that must be caged to avoid population decline. I found that in the absence of seed predation, the Lassics lupine population growth rate would be quite robust (λs = 1.17), but without continued human intervention (i.e., caging), the current rate of seed predation is projected to drive the population to extinction (λs = 0.92). Remarkably, the LTREs revealed that in order to best forestall population decline, plants should be caged at roughly the same proportions as they are under current management practices. Early identification by managers of the role of seed predation in Lassics lupine population decline was likely instrumental in the prevention of a substantial reduction in population size. The success of the current efforts can only be considered a deferment, however, and without further research into the underlying causes of this untenable seed predation rate, the Lassics lupine could be unable to recover.
Recommended Citation
Kurkjian, Helen, "A population viability analysis of the Lassics lupine (Lupinus constancei)" (2012). Cal Poly Humboldt theses and projects. 1544.
https://digitalcommons.humboldt.edu/etd/1544
https://scholarworks.calstate.edu/concern/theses/pc289m30r