Population modelling of Great Crested Newts (Triturus cristatus)

Summary Population Viability Analysis (PVA) provides a tool for assessing the risk of extinction in threatened species, but has rarely been applied to amphibian populations. Using existing life history data, we constructed several stochastic models to predict the effects of (1) progressive subdivision of crested newt habitat; and (2) different levels of juvenile dispersal between ponds, on the persistence of crested newt populations over a fifty year period. The models predict that small isolated populations have a higher risk of extinction than large isolated populations. In a subdivided population, increasing dispersal between subpopulations decreased the extinction risk of the metapopulation as a whole. Although the extinction risk of an individual isolated population is relatively high, the collective extinction risk of a group of such populations is lower than that of a single population with the same overall population size, even in the absence of dispersal. This appears to be a result of the asynchronous population dynamics that are generated in a group of isolated populations. A subdivided population may therefore persist for longer than a single population because it is unlikely that all the subpopulations will go extinct at the same time.