WERC Publication Brief: Long-term data clarifies desert tortoise growth, maturity and survivorship parameters. Updated October 2012.
THIS BRIEF REFERS TO:
Medica, PA, KE Nussear, TC Esque, MB Saethre. 2012. Long-term growth of desert tortoises (Gopherus agassizii) in a southern Nevada population. Journal of Herpetology 46(2): 213:220. doi: 10.1670/11-327
Data on the life history parameters of the Agassiz’s desert tortoise (Gopherus agassizii
) are necessary to develop accurate population viability analyses, which will allow land managers to make more informed decisions with regard to desert tortoise populations.
Long-term mark-release-recapture studies provide the best means of obtaining the most accurate information on life history characteristics such as growth, age at maturity, and survivorship.
A USGS study by Phil Medica, Ken Nussear, Todd Esque and Mary Saethre in the Journal of Herpetology
reports on the growth, age at sexual maturity and survivorship of a cohort of 17 known-age, semi-wild desert tortoises over a 47 year period.
Growth of desert tortoises was positively correlated with the amount of winter rainfall and production of ephemeral plants. Winter rainfall and ephemeral plant production are highly correlated and served as equivalent predictors of annual growth of desert tortoises.
Desert tortoise growth was linear and not significantly different between sexes until tortoises reached the early to mid-20’s in age. The inflection point of reduced growth in desert tortoises coincided with reaching sexual maturity. At this inflection point growth slowed for both sexes, but females grew significantly less than males.
Survivorship of this cohort averaged 43 years, notably less than the estimate of 50 to 100 years used in previous population viability analyses. Over the course of the study, mortality of adult desert tortoises was primarily caused by stochastic events, such as predation and drought.
Long-term studies are cruicial to obtain accurate information and clarify historic assumptions on tortoise life history parameters, such as growth and survivorship. Image credit: Ken Nussear/USGS.
The following files are related to this product:
Some files associated with this product may require the ability to read Portable Document Format (PDF) documents; the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge