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Abstract Detail

Conservation Biology

Deprenger-Levin, Michelle [1], Ramp Neale, Jennifer M. [1], Grant III, Thomas A. [2], Dawson, Carol [3].

Population Viability Analyses based on thirteen years of demographic data predict a grim future for the skiff milk vetch (Astragalus microcymbus), where can we go from here?

Astragalus microcymbus Barneby (Fabaceae) is a rare species endemic to Gunnison County, Colorado. Since 1995, Denver Botanic Gardens and the Bureau of Land Management (Colorado State Office) have monitored four populations of this sensitive species in the South Beaver Creek drainage. Large, statistically significant population declines have been documented. The demographic study has documented prolonged dormancy, episodic fruit production, and variable levels of leaf and inflorescence herbivory. Count-based and stage-based population viability analyses were conducted using the demographic data. The count-based PVA, a coarse analysis, indicates that the populations are declining at an average rate of 10% per year with individual populations declining at rates of 6-13% per year. A quasi-extinction threshold of 20 individuals was set for each site. Time to extinction for the populations ranged from 12-35 years with all populations extirpated within 35 years after study initiation. The stage-based PVA, a fine-scale analysis, was conducted on all data collected through 2008. The analysis indicates a flat to slightly declining population projection with an estimated decline of 5% per year. Despite the differences in growth rate between the two analyses, both indicate a decrease in population size over time indicating that management is needed to prevent these populations from extirpation. Additional sensitivity analyses to detect which life-stage is most sensitive to shifts will direct future management for this species to maintain population size.

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1 - Denver Botanic Gardens, Research & Conservation, 909 York Street, Denver, CO, 80206, USA
2 - Colorado State University, Graduate Degree Program in Ecology, Fort Collins, CO, 80523, USA
3 - U.S. Bureau of Land Management (BLM) - Colorado State Office, 2850 Youngfield Street, Lakewood, CO, 80215, USA

Demographic Monitoring
Population Viability Analysis (PVA)

Presentation Type: Oral Paper:Papers for Topics
Session: 58
Location: Wasatch A/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 8:45 AM
Number: 58004
Abstract ID:678