Dissertation/Thesis Abstract

Evaluating monitoring strategies and habitat for tortoises in the Sonoran desert
by Zylstra, Erin Rae, M.S., The University of Arizona, 2008, 66; 1457397
Abstract (Summary)

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.

Indexing (document details)
Advisor: Steidl, Robert J.
Commitee: Schwalbe, Cecil R., Shaw, William
School: The University of Arizona
Department: Natural Resources
School Location: United States -- Arizona
Source: MAI 47/01M, Masters Abstracts International
Subjects: Ecology
Keywords: Desert tortoise, Detection probability, Gopherus agassizii, Habitat, Monitoring, Site occupancy
Publication Number: 1457397
ISBN: 978-0-549-79352-6
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