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Contributed Talk

Session: : Conservation Ecology and Extinction 6

COS 281-2 - Climatic drivers of Mojave desert tortoise survival

Thursday, August 10, 2023
1:45 PM – 2:00 PM PDT
Location: C125-126
Abstract: Survival is a key demographic process that can result in population growth or decline. Its influence may be especially pronounced in long-lived species that inhabit extreme or dynamic environments The life history of the federally-listed Mojave desert tortoise is typified by high annual survival rates. However, survival rates may be influenced by droughts and heat waves, which have become more prevalent and intense in the range of the species. Understanding how these climatic processes alter tortoise survival is important to predicting how tortoise populations will fare in future climate scenarios. We leveraged long-term tortoise telemetry datasets from Nevada and California to model annual survival using a Bayesian known-fate model. Our datasets came from 17 different sites, span three decades (1992 through 2022), and included data from 821 individual tortoises. Specifically, we examined how individual-level covariates (age class, sex) and climate covariates determined annual survival. We used sliding climate window analyses on past precipitation and temperature data to determine how to best parameterize these covariates. We found that adult male tortoises had higher survival rates than females, and that juvenile tortoises had a lower survival rate than adults. Tortoise survival was positively related to the amount of precipitation in the previous and concurrent year while negatively related to the average monthly maximum temperature of the prior active season. These results suggest that hold over effects of the prior year are important in determining tortoise survival, providing context for how future climates may affect tortoise demography.