Document: CUR-3-81-7

Desert tortoise reproduction: The influence of female size and abiotic factors on fecundity.

BJURLIN, C.D.* and J.A.BISSONETTE

Utah State University Logan Utah 84322 USA 1

Abstract:
Reliable estimates of vital rates (i.e., fecundity, survival, and growth) are of primary importance in the stewardship of threatened and endangered species, but these data are not often available throughout the geographic range of the organism. Such is the case for the desert tortoise (Gopherus agassizii), recently listed as a federally threatened species. From 19971999 we used radiographic techniques to determine prenatal egg production of a western Mojave population of the desert tortoise. Our findings corroborated past research: Total egg production (F1,21 = 4.68; P < 0.05) and size of the first clutch (F1,21 = 9.12; P < 0.01) increased with female body size. However, our data did not support a previous finding of positive correlation between female size and egg size. The resolution of this inconsistency is not trivial, since larger eggs produced larger hatchlings (F3,12 = 81.009; P < 0.001) with potentially greater resources to survive periods of scarce desert plant production. Interestingly, incubation condition was as influential on hatchling morphometrics as variation in egg dimension. Eggs incubating during a wet year, when soil moisture was high, produced much heavier hatchlings than same-sized eggs incubating during a dry year. In summary, protection of larger female tortoises will yield more offspring, but will not necessarily insure greater investment in individual eggs. Abiotic factors, such as temperature and soil moisture of the nest chamber, may play a greater role in desert tortoise hatchling morphometrics than has been previously reported. Future work on size related survival of tortoise young is needed.

Keywords: Desert Tortoise, Vital Rates, Fecundity, Hatchling, Abiotic Factors, Nest Microhabitat

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This abstract is being presented at: 9:00 AM in session:
Oral Session #27: Salamanders, Lizards, and Tortoises.