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 using stochastic models constructed from existing life history data. The models predict that small isolated populations have a higher risk of extinction than large isolated populations. However, even large populations had a relatively high extinction risk over a fifty year period if they remained isolated. 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 decreased the extinction risk of the metapopulation as a whole. However, even in the absence of dispersal, a subdivided population had a lower overall extinction risk than a single isolated population of the same size. Environmental stochasticity may therefore result in asynchronous dynamics within subpopulations, which leads to the risk of extinction being spread across the subpopulations. Although population viability analysis has the potential to provide an objective assessment of population management decisions, it has not yet been a component of conservation planning for the crested newt in Britain.