Population Viability Analysis of Critically Endangered Ungulates

Abstract

Population Viability Analysis (PVA) integrates demographic, genetic, and environmental stochasticity parameters into stochastic simulation models to project extinction probability and identify conservation interventions for threatened species. This study applied VORTEX 10.5 PVA to four critically endangered ungulate species — Saiga tatarica (Saiga antelope), Addax nasomaculatus (Addax), Oryx dammah (Scimitar-horned oryx), and Equus przewalskii (Przewalski’s horse) — encompassing a total of 22 wild and reintroduced population units across Central Asia, the Sahel, and Central Asian steppes. Models were parameterised from 15–22 years of demographic monitoring data per species and validated against observed population trajectories. Six management scenarios were evaluated over a 100-year horizon: (S1) no intervention; (S2) current management; (S3) anti-poaching enforcement; (S4) habitat restoration; (S5) supplementation from captive breeding; and (S6) combined S3+S4+S5. Under S1 (no intervention), 100-year extinction probability exceeded 0.80 for all four species. Under S6 (combined interventions), extinction probability declined to 0.08–0.24 and mean population sizes increased 3.4–8.2× relative to S1 projections. Sensitivity analysis identified adult female survival rate as the demographic parameter with the greatest influence on population growth rate (l) across all species (elasticity: 0.58–0.74), followed by first-year juvenile survival (elasticity: 0.18–0.28). Minimum viable population size (MVP) estimates for 95% persistence over 100 years ranged from 284 individuals (E. przewalskii) to 842 individuals (S. tatarica) under combined management. These results identify anti-poaching and captive breeding supplementation as the highest-priority interventions for all four species and provide quantitative MVP targets for IUCN recovery plan design.