Age- and sex-specific survival of the Gunnison's prairie dog (Cynomys gunnisoni)

Abstract

Age- and sex-specific survival rates are essential for understanding animal population dynamics and discerning environmental influences on population parameters. To date, little research has been done on age- and sex-specific survival of the Gunnison's prairie dog (Cynomys gunnisoni), a colonial ground-dwelling squirrel inhabiting the sagebrush ecosystem of the southwestern United States. To discern impacts of the year of study, age, sex, and reproductive status on survival, we conducted a capture-mark-recapture analysis on a previously collected long-term dataset of a population of Gunnison's prairie dogs (n = 2508) from 1989 to 1995. We implemented two models: age-cohort Cormack–Jolly–Seber (CJS) models (to examine survival by age, sex, and year) and multistate mark-recapture models (to analyze survival by age and year, as well as breeding status). Females had higher apparent survival than males. Yearlings had a low apparent survival rate (0.288 ± 0.022, [±SE]) compared to juveniles (0.461 ± 0.019) and adults (0.482 ± 0.055). Less than 50% (48.0 ± 2.7) of female yearlings successfully weaned litters each year. Yearling survival rate was lower than other highly social prairie dog species that do not reproduce as yearlings, suggesting that there may be a cost to reproduction. We also constructed a postbreeding matrix population model and associated elasticity analysis, which indicated that the reproductive output of yearlings was the most significant potential driver of population growth. Our findings provide more nuanced estimates for age- and sex-specific survival in this species than were previously available and also more broadly inform linkages between demography and sociality in prairie dogs.