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Abstract Detail


Conservation Biology

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

Use of Population Viability Analysis (PVA) in the conservation of a rare and declining narrow endemic, Astragalus microcymbus (Fabaceae).

Astragalus microcymbus is a rare species endemic to Gunnison County, Colorado, found in 42 scattered populations representing approximately 10,000 plants. Since 1995, Denver Botanic Gardens and the Bureau of Land Management (Colorado State Office) have monitored four populations (~1500 plants). The demographic study has documented prolonged dormancy, episodic fruit production, and variable levels of leaf and inflorescence herbivory. Statistically significant population declines have been documented, followed by non-significant increases in population sizes since 2002. A count-based PVA 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 population. Time to extinction for the populations ranged from 12-35 years with all populations extirpated within 35 years after study initiation. This study is in the 12th year and immediate action is needed to prevent extirpation of these populations. A detailed stage-based PVA will be conducted to examine the sensitivity of each life-stage to changes in survival. Seed set in all populations is low with an average of 18% of individuals producing fruit in a given year. A seed bank study conducted in 2005 found only one A. microcymbus seed in 12 plots, indicating effectively no seed bank. In addition to low seed set, all populations suffer from high levels of herbivory each year, further reducing the number of seeds produced. Mammal exclusion plots were installed in the summer of 2006 to determine the effects of herbivory on the populations. Given the narrow range of this endemic species and the low level of seeds found in the seed bank study, herbivory may have a large, irreversible effect on this species as a whole. The results of the stage-based PVA will be used to direct future management.


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1 - Denver Botanic Gardens, Research, 909 York Street, Denver, CO, 80206, USA
2 - U.S. Bureau of Land Management (BLM) - Colorado State Office, 2850 Youngfield Street, Lakewood, CO, 80215, USA
3 - Denver Botanic Gardens, Research, Herbaria & Records, 909 York Street, Denver, CO, 80206, United States

Keywords:
Population Viability Analysis (PVA)
Demographic Monitoring
conservation.

Presentation Type: Poster:Posters for Topics
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P65006
Abstract ID:1744


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