New Zealand Journal of Botany abstracts
Is dispersal easier than pollination? Two tests in New Zealand Loranthaceae
Dave Kelly
Jenny J. Ladley
Biological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
Alastair W. Robertson
Ecology Group
Institute of Natural Resources
Massey University
Private Bag 11222
Palmerston North, New Zealand
Abstract We tested the relative frequency of pollen
limitation and dispersal limitation for two bird-pollinated and bird-dispersed
New Zealand mistletoes, Peraxilla tetrapetala and Alepis flavida,
at a South Island site where the bellbird (Anthornis melanura) is
the sole pollinator and disperser. There was no evidence of dispersal limitation
for P. tetrapetala over four seasons or A. flavida over two
seasons. Few ripe fruits were present on plants at any one time (usually
<5%), and more than 90% of the fruit crop was removed. A. flavida
was not pollen limited, but P. tetrapetala was significantly pollen
limited in 6 of 10 years. The presence of pollen limitation but not dispersal
limitation, despite both services depending on the same bird, is influenced
by the much faster rates of flower ripening per day compared with fruit ripening
(15-54 times faster in P. tetrapetala). In New Zealand, pollination
failure probably threatens at least as many plant species as dispersal failure.
In theory, dispersal should threaten fewer plant species, because dispersal
usually involves more animal species, makes smaller quantitative demands
on the dispersers (fewer fruits ripening per day, and fruits can wait longer
for attention), and may be less obligate for at least some reproduction to
occur.
Keywords agents of decline; Alepis flavida; bird
dispersal; disperser limitation; frugivory; Loranthaceae; mistletoe; mutualisms;
Peraxilla tetrapetala; pollinator limitation
B02086; Online publication date 30 March 2004; Received 20 December 2002;
accepted 10 September 2003
New Zealand Journal of Botany, 2004, Vol. 42: 89-103
0028-825X/04/4201-0089 © The Royal Society of New Zealand 2004
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