The tiny hunter Partula
Partula incrassa exigua
Partula exigua was one of the most restricted of all species, being found only in half a dozen valleys in north-eastern Moorea.It was overlooked until 1925 when Henry Crampton recognised it as distinct from its sister species P. taeniata.Crampton's name for it, 'exigua' means simply tiny, a rather unexciting name but reflecting that it was the smallest of the Partula. It has the unfortunate honour of being the first Partula to be driven to extinction by the invasion of the predatory snail Euglandian, by 1987 it had been lost.
What is ironic about this is that the centimetre long P. exigua was itself a predator. Dissections of wild collected specimens in the 1960s by Professors Bryan Clarke, Jim Murray and Mike Johnson found small snails in their guts. A more extensive dietary study based on the material collected in the 1960s has identified the prey as two minute tree snails: Georissa striata and Diastole conula (see pdf of the report). Jim Murray noted that after the extinction of the tiny hunter there was a dramatic increase in the numbers of the tiny black snails (Georissa) on the plants in that area.
Why was the tiny hunter Partula a predator? It was not exclusively a carnivore, in fact it only ate snails in one valley and all of them mainly fed on dead plant matter. It was probably eating other snails not for their meat, but for the calcium contained in their shells. Interestingly the shells of its strictly vegetarian sister species P. taeniata in the same valley were all fragile and clearly short of calcium.
Most aspects of Partula ecology still need to be investigated, over the next few years more answers will be posted here.
Other research on Partula
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