Studying Partula survival and recovery

Justin Gerlach

When I first became involved in Partula conservation in the early 1990s my main interest was in the impacts of the predatory snail Euglandina. At that time I developed a basic population model for partulid snails and Euglandina. This gave a reasonable representation of the pattern of extinction that had been observed in Polynesia. I subsequently realised that the model contained a number of errors. The model contained a number of errors and was based on completely the wrong approach. I am currently revising the population model and have developed a new version, that is simpler and more realistic. A refinement of this is that it allows modeling of the spread of Euglandina across each island. Testing this on Moorea gives a very accurate representation of what we know happened on that island. It also predicts that small populations of one species would survive in some parts of Moorea, even with the presence of the predators. These predicted areas precisely match where Partula taeniata survives today.

Now, though, Eugandina has been replaced as the main predator by the New Guinea flatworm Platydemus manokwari, so a new model is needed.

The reintroductions are providing new data and new approaches, which move us beyond modelling and my new focus is devising release methods that reduce the predation risk and identifying the best sites for partulid survival. This is all part of the reintroduction programme.

Other interests in Partula: