The abundance and persistence of Caprinae populations

Stable or growing populations may go extinct when their sizes cannot withstand large swings in temporal variation and stochastic forces. Hence, the minimum abundance threshold defining when populations can persist without human intervention forms a key conservation parameter. We identify this threshold for many populations of Caprinae, typically threatened species lacking demographic data. Doing so helps triage conservation and management actions for threatened or harvested populations. Methodologically, we used population projection matrices and simulations, with starting abundance, recruitment, and adult female survival predicting future abundance, growth rate (lambda), and population trend. We incorporated mean demographic rates representative of Caprinae populations and corresponding variances from desert bighorn sheep (Ovis canadensis nelsoni), as a proxy for Caprinae sharing similar life histories. We found a population's minimum abundance resulting in <= 0.01 chance of quasi-extinction (QE; population <= 5 adult females) in 10 years and <= 0.10 QE in 30 years as 50 adult females, or 70 were translocation (removals) pursued. Discovering the threshold required 3 demographic parameters. We show, however, that monitoring populations' relationships to this threshold requires only abundance and recruitment data. This applied approach avoids the logistical and cost hurdles in measuring female survival, making assays of population persistence more practical.

Automated summary

Stable or growing populations may face extinction when they cannot tolerate large fluctuations and random forces. This study aims to determine the minimum abundance threshold for Caprinae populations, which lack demographic data, in order to guide conservation and management actions. Using population projection matrices and simulations, the researchers found that a population with 50 adult females or 70 with translocation (removals) would have a low chance of quasi-extinction in 10-30 years. Monitoring the population's relationship to this threshold only requires abundance and recruitment data, making it a more practical approach.