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    Evaluating Monitoring Strategies and Habitat for Tortoises in the Sonoran Desert

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    Author
    Zylstra, Erin R.
    Issue Date
    2008
    Keywords
    desert tortoise
    detection probability
    Gopherus agassizii
    habitat
    monitoring
    site occupancy
    Advisor
    Steidl, Robert J.
    Committee Chair
    Steidl, Robert J.
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    Effective conservation requires efficient population monitoring, which can be challenging for rare species like the desert tortoise (Gopherus agassizii). We compared two alternative survey methods that can be used to monitor tortoise populations: distance sampling and site occupancy estimation. In 2005 and 2006 combined, we surveyed 120 1-km transects to estimate density and 40 3-ha plots with five presence-“absence” surveys to estimate occupancy of Sonoran desert tortoises in two mountain ranges in southern Arizona. We found that monitoring programs based on an occupancy framework were more efficient and had greater power to detect linear trends. We also found that habitat use by Sonoran desert tortoises was influenced most by slope and aspect, contrasting with patterns observed in the Mojave Desert. Given its efficiency, power, and ability to gauge changes in distribution while accounting for variation in detectability, occupancy offers a promising alternative for long-term monitoring of Sonoran desert tortoise populations.
    Type
    text
    Electronic Thesis
    Degree Name
    M.S.
    Degree Level
    masters
    Degree Program
    Natural Resources
    Graduate College
    Degree Grantor
    University of Arizona
    Collections
    Master's Theses

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