Montgomery, B. R.; Kelly, D.; Robertson, A. W.; Ladley, J. J. 2003. Pollinator behaviour, not increased resources, boosts seed set on forest edges in a New Zealand Loranthaceous mistletoe. New Zealand Journal of Botany 41: 277-286.
Abstract
The endemic New Zealand mistletoe Peraxilla tetrapetala
(Loranthaceae) has previously been shown to be pollinator limited, and
to experience higher fruit set in increasingly fragmented habitats,
but the mechanism for higher fruit set on edges has not been studied.
Edges could affect plant resources (through higher light) and/or pollinator
behaviour. This study measures the degree to which pollination and resource
limitation affect female reproductive success along a gradient of increasing
exposure to the forest edge. Forty-two plants in pairs at varying distances
from the forest edge were selected from within two Nothofagus
forest fragments in the 1999/2000 season, and on one plant in each pair,
all ripe undamaged flowers were hand-pollinated. Light levels and the
degree of edge exposure were measured for each plant, and path analysis
was used to determine the relationship of these variables to proportion
fruit set. In agreement with previous studies, unmanipulated plants
were found to be strongly pollen limited, especially in shady locations.
However, on plants receiving hand-pollination, fruit set was uniformly
high, and unaffected by edge exposure or light levels. Direct observation
of flower visitation rates by birds in the 2000/01 season showed edge
flowers were visited twice as often as interior flowers. These results
show that the higher fruit set on edges is due to visitation patterns
of pollinators, and not due to greater resource availability on edges.
This improved pollination on edges may help to buffer this declining
plant against local extinction.
Keywords:
bird pollination; edge effects; fragmentation; Loranthaceae; mistletoe; Peraxilla; pollinator limitation; resource limitation