Estimating Population Sizes, Viability and Sensitivity of the Crested Newt (Triturus cristatus) at a Landscape Scale
Population sizes, viability and sensitivity of the threatened amphibian crested newt (Triturus cristatus) were estimated in an area of 144 km2 in southeastern Sweden. Eighteen ponds were monitored during spring and summer 2004 using drift fence with pitfall traps, funnel traps, visual observation and netting. Estimated adult population sizes ranged between 0 and 620 individuals, and the mean (±SD) in local populations was 297 ±233 individuals. Viability with and without management, and sensitivity of different parameters were simulated with a demographically and spatially structured stochastic model. Due to uncertain data, the model was simulated with parameter ranges to estimate upper and lower bounds of viability.
Estimated quasi-extinction risk (the risk of each population in the study area falling below 10 females) within a 50-year period ranged from 100% to 0%, with a “best” estimate of 1.2%.
However, just by setting the most sensitive parameter, juvenile survival, to its lower bound, the quasi-extinction risk increased to nearly 100%. The sensitivity of juvenile survival points out the importance of focusing conservation efforts and research on this life stage. Management measures in form of restoration of ponds and increased pond density had only marginal effects on the quasi-extinction risk. Nevertheless, these measures decreased the risk for the species to end up below certain abundances after 50 years considerably, making the study populations more viable at a longer term. Concrete management measures for the study area are presented.