Wednesday, May 18, 2011

Modelling distribution of jellyfish with ANN

A new paper first-authored by David Pontin, my ex-PhD student from Lincoln University. This describes how he used MLP to model to presence and absence of a species of stinging jellyfish (Physalia physalis) at New Zealand beaches.

There are a couple of interesting points about this paper. Firstly, because there have been no surveys of Physalia distribution, a surrogate data set was used. This data set was stings recorded by lifeguards of Surf Lifesaving New Zealand. Since lifeguards treat jellyfish stings, each incident has to be recorded, and Physalia is the only stinging organism in New Zealand waters, a fairly large data set was available as to the presence of these jellyfish. Predictions were made from oceanic variables such as wave height and direction, and wind speed and direction.

Secondly, the data was carefully cleaned: since stings of swimmers was used as the surrogate for Physalia presence, times when there were no swimmers at the beach were excluded from the data set. While this introduced a small missing-not-at-random bias, it also removed a large number of false absences: if an example was recorded as an absence, then it was because there were no stings recorded, not because there was no one in the water.

Thirdly, an analysis of the contributions of each input of the ANN was performed. This showed which of the oceanic variables contributed the most to the presence of Physalia. This analysis indicated that there may be a hitherto unknown spawning ground for this species in the Tasman Sea.

Finally, and this is in many ways the focus of the paper, the contribution analysis of the ANN was compared with the results of input contribution analysis by an evolutionary algorithm.

Overall, this is a nice little paper that neatly sums up David's work and contributes to the understanding of the behaviour of Physalia. This shows how useful computational intelligence is to ecological applications, an area where there is, in my opinion, enormous potential for computational intelligence researchers to make real, meaningful contributions.