The biology of Placostylus ambagiosus (Pulmonata: Bulimulidae) in New Zealand: Part 1. Behaviour, habitat use, abundance, site fidelity, homing and the dimensions of eggs and snails

Abstract

The large land snail Placostylus ambagiosus (Pulmonata: Bulimulidae) was investigated during a long-term study in northernmost New Zealand. The snails fed at night on fallen leaves from a variety of broadleaf trees and bushes. During the day, most snails in shrubland rested under plants close to their food sources at densities of up to 53 snails per m² and mean live biomasses of 47–72 g/m². Individual snails stayed close to their food plants for up to 12 years, seldom moving away. Resting behaviour and site fidelity in forest was not investigated in detail, but some adult snails in forest returned to their original sites after being moved up to 60 m into a fenced area built to protect them from feral domestic animals. The ovoid eggs (mean 7.0 mm long×5.6 mm wide; ranges 5.5–7.7 mm long; 5.1–6.7 mm wide) were laid in clutches averaging 43 eggs (range 1–113 eggs) in shallow cavities covered with soil. More than one snail may contribute to a clutch. Adult shell height ranged from 43 mm to 97 mm and varied with habitat quality. Where snail abundance was high adults were small. Implications of these results for conservation management are discussed.

Keywords:

• long-term monitoring
• resting site
• clutch size
• biomass
• conservation management

Acknowledgements

We thank the following who assisted with many days of field work: Tristan Armstrong, Paul Barrett, Suzanne Bassett, Andrea Booth, Murray Efford, Ian Flux, Diane Gleeson, Elizabeth Grant, Katrina Hansen, Tracy Harris, Ruth Henry, Leigh Honnor, Maree Hunt, Carrie Jane, Jens Jorgensen, Cathy Lake, Gary Land, Megan McLean, Peter MacGregor, Nigel Miller, Kahori Nagakawa, Carol Nicholson, Richard Montifiore, Graeme Murtagh, Richard Overwijk, Gerard Pilon, Tony Porteous, Stephanie Prince, Christine Reed, Tim Shaw, Michele Salas, Catherine Yong.

The field staff of the Department of Conservation provided extensive practical support and included Whiti Abahams, Mike Aviss, Trevor and Gail Bullock, Nik Conrad, Francis Fitzpatrick, Rod Green, Simon Job, Alan and Willie McCrae, Bill McLeod, DJ Neho, Siebert Rohiopa, Eddie Smith and Aileena Sucich. We thank Don Newman and two unknown reviewers for constructive criticism of the text, and Sandra Parkkarli and Chris Edkins for preparing the figures. This research was supported by DOC (Science Investigation No. 2386) and Massey University.