Sex ratios, fruit set and size-class structure in the threatened, gynodioecious, sand-dune species Pimelea arenaria (Thymelaeaceae) from New Zealand
Merilyn F. MerrettLandcare Research, Private Bag 3127, Hamilton, New Zealand. Present address: The Open Polytechnic of New~Zealand, Private Bag 31 914, Lower Hutt, New~Zealand. Email: merilyn.merrett@openpolytechnic.ac.nz
Australian Journal of Botany 55(5) 554-560 https://doi.org/10.1071/BT06017
Submitted: 31 January 2006 Accepted: 8 February 2007 Published: 17 August 2007
Abstract
Pimelea arenaria sens. str. Cunn. is one of a small suite of native species that occur exclusively on unconsolidated sand dunes and in dune hollows of the North Island and Chatham Islands of New Zealand. It has become extinct at several beaches, and is currently listed in the Gradual Decline category of threatened plants. Eighteen populations of P. arenaria from throughout the North Island of New Zealand were investigated to determine sex ratios, fruit set and population size-class structures. Sex ratios were variable among the 18 study populations; the proportion of females was higher in populations in the northern half of the North Island (15.9–45.5%) than in populations from Kawhia southwards (0–12.7%). Females were absent from three south-western coastal populations. Although fruit set was relatively high, averaging 47% for female and 68% for hermaphroditic plants, recruitment failure was evident at most of the 18 sites surveyed. There was no evidence that sex ratios or fruit set were factors contributing to recruitment failure. Although most of the populations surveyed are not under immediate threat, lack of recruitment could affect population persistence in the long term.
Acknowledgements
I thank Edna Leet, Neil Fitzgerald, Katie Cartner, David Burnett, Diane Miller and Jim Campbell (Department of Conservation, Wanganui) and Garry Foster (Department of Conservation, Masterton) who helped at various times with fieldwork; the curators of AK, CHR and WAIK for access to herbarium records; Craig Briggs for producing Fig. 1; and Greg Arnold for statistical advice. Comments from Alastair Robertson, Bruce Burns, Bill Lee and three anonymous referees greatly improved the manuscript. This research was funded by the Foundation for Research, Science and Technology (Contracts C09X0204 & C09X0205).
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