Modelling population dynamics of great crested newts (Triturus cristatus):A population viability analysis

The effects of pond isolation, drought, habitat fragmentation and dispersal on populations of crested newts (Triturus cristatus) were investigated usi ng stochastic models constructed from existing life history data. The model s predict that small isolated populations have a higher risk of extinction than large isolated populations. However, even large populations had a rela tively high extinction risk over a fifty year period if they remained isola ted. Pond desiccation affects metamorphic success and recruitment, and the risk of extinction decreased with decreasing frequency of regional droughts . In a subdivided population, increasing dispersal between subpopulations d ecreased the extinction risk of the metapopulation as a whole. However, eve n in the absence of dispersal, a subdivided population had a lower overall extinction risk than a single isolated population of the same size. Environ mental stochasticity may therefore result in asynchronous dynamics within s ubpopulations, which leads to the risk of extinction being spread across th e subpopulations. Although population viability analysis has the potential to provide an objective assessment of population management decisions, it h as not yet been a component of conservation planning for the crested newt i n Britain.