New Zealand Journal of Botany abstracts
Limitations on recruitment of the rare sand daphne Pimelea
arenaria (Thymelaeaceae), lower North Island, New Zealand
P. A. C. Dawson
G. L. Rapson*
A. W. Robertson
R. A. Fordham
Ecology Group
Institute of Natural Resources
Massey University
Private Bag 11-222
Palmerston North, New Zealand
*Author for correspondence: G.Rapson@massey.ac.nz.
Abstract Pimelea arenaria, an endangered
native sand dune plant, appears to be experiencing recruitment failure.
The structure of four populations from the lower North Island, New
Zealand, was examined for recruitment patterns, while one population
was examined for flowering, pollination, and seed germination limits on
regeneration. Line transects and searches found no seedlings, and
measures of individual plant sizes (n = 331) showed bias towards
medium, with some large, individuals, suggesting recruitment failure at
all sites. Flowers are plentiful. The standing crop of nectar was
c. 0.4–0.9 joules per hermaphrodite flower, with insects appearing
to be the main pollen vectors. Pollination manipulations were carried
out on both genders at one site, with fruit set measured from natural,
hand out-crossed, and pollinator-exclusion treatments. Female flowers
do not appear to be pollen limited as natural fruit set is only
non-significantly lower than that in hand-outcrossed flowers. Only
hermaphrodite plants selfed autonomously, with nearly 90% producing
fruit. One quarter of the seed from both female and hermaphrodite
flowers germinated. Results suggest that recruitment failure of Pimelea
arenaria is not due to reproductive biology, pollen limitation, or
poor seed germination. Therefore, recruitment failure probably occurs
during the seedling establishment phases, due to environmental
pressures and/or predation.
Keywords Pimelea arenaria; sand dunes;
regeneration; pollination; fruit set; population structure
B04025; Received 7 July 2004; accepted 13 May 2005; Online
publication date 15 July 2005
New Zealand Journal of Botany, 2005, Vol. 43: 619–630
0028–825X/05/4303–0619 © The Royal Society of New Zealand 2005
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