Demography of two landsnail populations (Placostylus ambagiosus, Pulmonata: Bulimulidae) in relation to predator control in the far north of New Zealand Original Research Article

Two Placostylus ambagiosus populations were studied in New Zealand for 8 years to determine if poisoning rodent predators in the habitat of one population resulted in increased adult snail recruitment. ‘Pulse’ poisoning four times a year commenced a year after the study started in a population of Placostylus ambagiosus paraspiritus. A significant increase in the proportions of all juvenile snails with shells larger than 10 mm long was observed. The only other comparable population of this highly endangered snail species, P. a. michiei, was 33·7 km to the east. Here, predation mostly by birds had a similar effect on reducing adult snail recruitment as rodents did on P. a. paraspiritus. No predator control was done at the site occupied by P. a. michiei, and adult snail recruitment remained low throughout the study. This suggests that long-term pulse poisoning of rodents in remnant ‘islands’ of native habitat on the New Zealand mainland can be beneficial to the recovery of a landsnail population.