Population Viability Analysis of Flat-tailed Horned Lizards in the Yuma Desert Management Area

Grimsley, Ashley A.

Leavitt, Daniel J. *

Ingraldi, Michael F.

Wildlife Contracts Branch

Arizona Game and Fish Department

Phoenix, AZ USA


*Current affiliation

Naval Air Weapons Station,

China Lake, CA USA

The Flat-tailed Horned Lizard (Phrynosoma mcallii) is distributed within a limited range, including extreme southwestern Arizona, southern California, and Sonora and Baja California, Mexico. Human expansion from both agricultural and urban development has caused significant habitat and range reduction. In order to determine the vulnerability of populations and relative risk of extinction of P. mcallii in Arizona, we carried out a structured population viability analysis (PVA) using demographic and occupancy data collected in the Yuma Desert from 2008 to 2015. Results suggested a low risk of population extinction (0.07 ± 0.01) over the next 100 years. Deterministic results showed a positive annual rate of change (lambda = 1.08) and a positive exponential rate of increase (r = 0.08). The exponential rate of increase for the stochastic results was also positive (rs = 0.02 ± 0.001), and the mean time to first extinction was 56 ± 3 years. Sensitivity analyses revealed potential drivers of population growth are related to reproduction and mortality. Specifically, results show future monitoring and research should be focused on evaluating the age at first offspring, reproductive success, clutch size, percent of females breeding, percent of females producing multiple broods, and drivers of mortality dynamics to enhance our understanding of these factors on population persistence. Finally, we determined that management should be considered when the Yuma Desert population size is near 122,309 or lower, based on a 30% decline in current population numbers. Future efforts will be focused on conducting a meta-population PVA of P. mcallii populations range-wide.