Abstract

AbstractDemographic models enhance understanding of drivers of population growth and inform conservation efforts to prevent population declines and extinction. For species with complex life histories, however, parameterizing demographic models is challenging because some life stages can be difficult to study directly. Integrated population models (IPMs) empower researchers to estimate vital rates for organisms that have cryptic or widely dispersing early life stages by integrating multiple demographic data sources. For a stream‐inhabiting frog (Rana boylii) that is declining through much of its range in Oregon and California, USA, we collected egg‐mass counts and capture–mark–recapture data on adults from two populations in California to fit IPMs that estimate adult abundance and the survival rate of both marked and unobserved life stages. Estimates of adult abundance based on long‐term monitoring of egg‐mass counts showed that study populations fluctuated greatly inter‐annually but were stable at longer timescales (i.e., decades). Adult female survival during 5–6 yr of capture–mark–recapture study periods was nearly equal in each population. Survival rate of R. boylii eggs to the subadult stage is low on average (0.002) but highly variable among years depending on post‐oviposition stream flow. Population viability analysis showed that survival of adult and subadult life stages has the greatest proportional effect on population growth; the survival of egg and tadpole life stages, however, is more malleable by management interventions. For example, simulations showed head‐starting of tadpoles, salvaging stranded egg masses, and limiting aseasonal pulsed flows could dramatically reduce the threat of extirpation. This study demonstrates the value of integrating multiple demographic data sources to construct models of population dynamics in species with complex life histories.

Highlights

  • Species extinction is occurring at an unprecedented rate (Barnosky et al 2011, IPBES 2019)

  • The CJS (P = 0.36) and eggmass count sub-models (P = 0.56) of the Fox Creek Integrated population models (IPMs) showed no evidence of a lack of fit to the observed data

  • There was no evidence for differences in survival and recapture rates between female and male R. boylii at Fox Creek

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Summary

Introduction

Species extinction is occurring at an unprecedented rate (Barnosky et al 2011, IPBES 2019). Demographic knowledge at a fine-grained level of detail is essential (Akçakaya and Sjogren-Gulve 2000), because species may face disparate stressors across their ranges, and life stages within a species can display incongruent risks from similar stressors (Otero et al 2011, Sturrock et al 2020). Structured population models, which condense demography into a few key age- or stage-specific vital rates, have proven useful for identifying the environmental factors, biological traits, and anthropogenic stressors driving growth or decline (Brook et al 2000, Caswell 2001). We develop an integrated population model (IPM) to quantify the efficacy of measures, including the management of water flow in rivers with dams, designed to minimize extinction risk of an imperiled frog. We address the difficulties of vital rate estimation for hard-to-study life stages

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