Morphological variation, biogeography and local extinction of the northern New Zealand landsnail Placostylus hongii (Gastropoda: Bulimulidae)

Placostvlus hongu (Lesson) is recorded from sites between Whangaroa and Whangarei on the mainland Northland coast, and from the Poor Knights, Chicken, Mokohmau and Great Barrier Islands offshore There is considerable variation in shell morphology between the various populations, commonly with marked morphological divergence at a local scale but with overlapping variation overall across all populations of the taxon Patterns of morphological variation show no clear geographic trends and are at least in part related to local environmental factors Correlations are identified between shell shape and substratum type, and between shell size and vegetation type

Placostvlus hongu has a very restricted stratigraphic distribution in mainland Northland, with most if not all of the tew known fossil populations post‐dating Polynesian settlement at c 900–700 years BP We suggest that P hongii populations on the Poor Knights and possibly also those on the Mokohinau Is are endemic, whereas the mainland populations and those on Great Barrier and the Chicken Is have originated from anthropic redistribution of snails in prehistoric time A high proportion of the mainland P hongii populations and some offshore island populations became extinct in the last tew hundred years as a result of predation by introduced mammals and the modification and destruction of shrubland and foiest habitat

Keywords:

• landsnail
• Placostylus hongu
• biogeography
• extinction
• variation

Notes

Department of Conservation, P O Box 842, Whangarei, New Zealand

School of Biological Sciences University of Auckland, Private Bag 92019 Auckland, New Zealand