DEMOGRAPHY OF 2 LANDSNAIL POPULATIONS (PLACOSTYLUS-AMBAGIOSUS, PULMONATA, BULIMULIDAE) IN RELATION TO PREDATOR CONTROL IN THE FAR NORTH OF NEW-ZEALAND

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 i n a population of Placostylus ambagiosus paraspiritus. A significant i ncrease in the proportions of all juvenile snails with shells larger t han 10 mm long was observed. The only other comparable population of t his highly endangered snail species, P. a. michiei, was 33.7 km to the east. Here, predation mostly by birds had a similar effect on reducin g adult snail recruitment as rodents did on P. a. paraspiritus. No pre dator control was done at the site occupied by P. a. michiei, and adul t snail recruitment remained law throughout the study. This suggests t hat long-term pulse poisoning of rodents in remnant 'islands' of nativ e habitat on the New Zealand mainland can be beneficial to the recover y of a landsnail population. (C) 1998 Elsevier Science Ltd. All rights reserved.