Range-wide occupancy trends for the Mojave desert tortoise (Gopherus agassizii)

Amanda M. Kissel, Bryan Wallace, Jesse Anderson, Brett G. Dickson, Kristen Van Neste, Vincent Landau, Roy C. Averill-Murray, Linda J. Allison, Amy Fesnock

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Data from long-term monitoring programs, such as the US Fish and Wildlife Service (USFWS) line distance sampling (LDS) program for Mojave desert tortoises (Gopherus agassizii), are increasingly being used in new ways to elucidate trends in population dynamics. We used the USFWS LDS data in a novel way to generate range-wide predictions of occupancy, colonization, and local extinction rates from 2001 to 2018. We developed a dynamic occupancy model to answer fundamental questions posed by Bureau of Land Management personnel regarding how G. agassizii are distributed across the landscape over space and time. We transformed the LDS data into detection/nondetection data and constructed a Bayesian dynamic occupancy model using several time-varying (e.g., temperature, precipitation, normalized difference vegetation index, fire, and a proxy for invasive grasses) and static covariates (e.g., soil properties, topography, distance to roads, distance to urban areas) hypothesized to influence G. agassizii occupancy dynamics. We estimated that over the entire time series (2001–2018) the probability of G. agassizii occupancy is declining in over one quarter (26%) of the range, largely in the northeastern part of the range, but that from 2011 to 2018, 77% of the range has a declining trend. Drawing on these model outputs, we developed an interactive, web-based tool for exploring trends in dynamic occupancy across the species range, allowing users to focus on areas of management interest or concern.

Original languageEnglish (US)
Article numbere4462
JournalEcosphere
Volume14
Issue number3
DOIs
StatePublished - Mar 2023
Externally publishedYes

Keywords

  • Bayesian modeling
  • Gopherus agassizii
  • colonization probability
  • dynamic occupancy
  • extinction probability
  • management tools
  • population trends

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology

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