Some aspects of behaviour and ecology of the land snail Powelliphanta traversi traversi Powell (Rhytididae: Rhytidinae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University
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Date
1997
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Massey University
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Abstract
Powelliphanta traversi traversi Powell was studied at two sites in the Horowhenua. The use of an harmonic radar allowed the snails to be relocated, and followed for 20 months in their natural habitat. Morphometrics, population sizes, diet, movement, dispersal, and predation were examined. Different formae (morphs) lived at each site but mean shell lengths (43.2 mm at Papaitonga, 42.41 mm at Makahika) did not significantly differ. Frequency histograms of shell length for live and dead P. t. traversi were of similar shapes and there were few small shells. This could suggest that mortality was constant regardless of age, that young grow rapidly, or they live for a long time once full sized. The mean growth of new shell to the lip of the shell was found to be 1.71 mm (range 0.11 - 6.82 mm).The densities were not significantly different at each study site at 282 snails ha-1 for Papaitonga and 300 snails ha-1 at Makahika. A significantly positive correlation was found between P. t. traversi presence and leaf litter depth. Karaka (Corynocarpus laevigatus) was the only plant that was consistently found in quadrats with high snail numbers. The number of empty shells in a quadrat was a poor predictor of the number of live snails present. P. t. traversi were nocturnal and moved slowly in comparison to the garden snail H. aspersa. P. t. traversi were not active continuously though the night, and moisture related factors were the only significant predictors of movement. The most active snail moved 152 m in 107 days. Maximum displacement from point of origin averaged 49.8% of total movement. I suggest movement could be random, but appeared to adhere to a home-range. Limited dispersal suggested that fragmented P. t. traversi colonies should be considered discrete populations. The primary predator of P. t. traversi was the ship rat Rattus rattus. There was no evidence of predation from the brushtail possum, Trichosurus vulpecula, an important Powelliphanta predator in other localities. Diet and water uptake of P. t. traversi was examined in the laboratory. P. t. traversi appeared not to drink, but rather obtained water via integumentary absorption. Full hydration was reached in around three hours. Earthworms were the only food items consumed in this study. The snails did not forage in dry conditions.
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Snails, New Zealand