Spatial and temporal variation in survival of a rare reptile: A 22-year study of Sonoran desert tortoises

Erin R. Zylstra, Robert J. Steidl, Cristina A. Jones, Roy C. Averill-Murray

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


Although many species may be vulnerable to changes in climate, forecasting species-level responses can be challenging given the array of physiological, behavioral, and demographic attributes that might be affected. One strategy to improve forecasts is to evaluate how species responded to climatic variation in the past. We used 22 years of capture-recapture data for Sonoran desert tortoises (Gopherus morafkai) collected from 15 locations across their geographic range in Arizona to evaluate how environmental factors affected spatial and temporal variation in survival. Although rates of annual survival were generally high (Φ = 0.92), survival of adults decreased with drought severity, especially in portions of their range that were most arid and nearest to cities. In three locations where large numbers of carcasses from marked tortoises were recovered, survival of adults was markedly lower during periods of severe drought (Φ = 0.77-0.81) compared to all other periods (Φ = 0.93-0.98). Assuming continued levels of dependency of humans on fossil fuels, survival of adult tortoises is predicted to decrease by an average of 3 % during 2035-2060 relative to survival during 1987-2008 in 14 of the 15 populations we studied. This decrease could reduce persistence of tortoise populations, especially in arid portions of their range. Temporal and spatial variation in drought conditions are important determinants of survival in adult desert tortoises.

Original languageEnglish (US)
Pages (from-to)107-116
Number of pages10
Issue number1
StatePublished - Sep 2013


  • Capture-recapture
  • Climate change
  • Demography
  • Drought
  • Gopherus morafkai

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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