Applying stochastic and Bayesian integral projection modeling to amphibian population viability analysis

Integral projection models (IPMs) can estimate the population dynamics of species for which both discrete life stages and continuous variables influence demographic rates. Stochastic IPMs for imperiled species, in turn, can facilitate population viability analyses (PVAs) to guide conservation decision-making. Biphasic amphibians are globally distributed, often highly imperiled, and ecologically well suited to the IPM approach. Herein, we present a stochastic size- and stage-structured IPM for a biphasic amphibian, the U.S. federally threatened California tiger salamander (CTS) (Ambystoma californiense). This Bayesian model reveals that CTS population dynamics show greatest elasticity to changes in juvenile and metamorph growth and that populations are likely to experience rapid growth at low density. We integrated this IPM with climatic drivers of CTS demography to develop a PVA and examined CTS extinction risk under the primary threats of habitat loss and climate change. The PVA indicated that long-term viability is possible with surprisingly high (20%-50%) terrestrial mortality but simultaneously identified likely minimum terrestrial buffer requirements of 600-1000 m while accounting for numerous parameter uncertainties through the Bayesian framework. These analyses underscore the value of stochastic and Bayesian IPMs for understanding both climate-dependent taxa and those with cryptic life histories (e.g., biphasic amphibians) in service of ecological discovery and biodiversity conservation. In addition to providing guidance for CTS recovery, the contributed IPM and PVA supply a framework for applying these tools to investigations of ecologically similar species.

Automated summary

Integral projection models (IPMs) and population viability analyses (PVAs) are valuable tools for understanding and conserving imperiled species. In this study, a stochastic IPM was developed for the California tiger salamander (CTS) and integrated with climatic drivers to assess the extinction risk of CTS under habitat loss and climate change. The results showed that CTS populations are most sensitive to changes in juvenile and metamorph growth and indicated the importance of terrestrial buffer zones for long-term viability. This study highlights the importance of stochastic and Bayesian IPMs for understanding climate-dependent and cryptic species and provides a framework for similar ecological investigations.