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Pollination ecology of Tasmanian leatherwood (Eucryphia lucida Eucryphiaceae Labill.) and the impacts of hive honeybees

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Mallick, SA (2001) Pollination ecology of Tasmanian leatherwood (Eucryphia lucida Eucryphiaceae Labill.) and the impacts of hive honeybees. PhD thesis, University of Tasmania.

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Abstract

Tasmanian leatherwood (Eucryphia lucida Labill.) is a tall (up to 30 m) native
tree occurring as a canopy co-dominant in Tasmania's cool temperate rainforest.
A large proportion (ca. 37%) of E. lucida's total distribution occurs within the
Tasmanian Wilderness World Heritage Area. The nectar of E. lucida is used in
the production of leatherwood honey and is highly sought after by commercial
apiarists.
I investigated the impacts of commercially managed honeybees on E. lucida and
its native pollinators. Because the type and severity of honeybee impacts are
intimately related to the pollination system of the forage species, I also
examined aspects of the pollination ecology of E. lucida.
Flowers of E. lucida are relatively long-lived (12-13 days) and protandrous, with
around 6-7 days of pollen presentation followed by 6 days of stigma receptivity. -
However, the degree of overlap between the male and female phases of anthesis
depends on the rate at which pollen is removed from anthers by insect visitors
(i.e. flowers are facultatively protandrous). E.lucida flowers secrete a relatively
dilute nectar (ca. 20% sugar wt/wt) from nectaries at the bases of the stamens.
Nectar is secreted continuously, although secretion rates are substantially lower
at night. Flowers typically contain small volumes of liquid nectar in the early
morning which on warm days is rapidly concentrated through evaporative water
loss to > 60% wt/wt. This concentrated nectar is highly attractive to insects and
flowers typically receive multiple insect visits over a single day.
E. lucida is partially self fertile. Fruit and seed set in bagged flowers which
received a superabundance of autogamous self pollen (34% fruit set and 16 %
seed set) was relatively low compared to fruit and seed set in un-bagged flowers
(80% fruit set and 36% seed set). Stigmas of un-bagged flowers carried large
amounts of pollen (estimated at 1700 grains/stigma), and E. lucida flowers do
not appear to be pollen limited. Flowers of E. lucida received visits from a broad range of native diurnal insects
(dipterans;16 families, coleopterans; 6 families, hymenopterans; 5 families, and
lepidopterans; 2 families) and nocturnal insects (tipulid flies, elaterid beetles,
blattellid cockroaches, and geometrid and pyralid moths), as well as from the
introduced honeybee. E. lucida flowers also supported a range of squatter
insects which used the flowers as a semi-permanent refuge (mainly thrips,
staphylinid beetles, and spiders). Visitation rates varied enormously between sites, ranging from < 2 to > 25 visits per flower per 10-hour day. Nocturnal
visitation rates were < 2 visits per flower per 10-hour night. Large dipterans and
large coleopterans appeared to be the most important native pollinators of E.
lucida.
E. lucida appears to be well adapted for maximising pollination under
conditions of temporal and spatial heterogeneity in the native pollinator service.
Nectar production is independent of temperature, humidity and local shading,
and flowers rapidly accumulate nectar sugar on cold days when insects are
inactive. E. lucida flowers do not reabsorb accumulated nectar sugar. In
contrast, the rate of anther dehiscence is strongly and positively dependent on
temperature above 10°C, so that pollen release is retarded on cold days. The
resulting patterns of nectar and pollen release appear to maximise both male and
female function in E. lucida flowers under a broad array of weather and
pollinator-abundance conditions.
I examined the impacts of hive bees at 13 sites, 7 in the vicinity of a commercial
apiary and 6 control sites located >2 km from the nearest apiary (hive bees
foraged within 2 km of hives during E. lucida flowering). Honeybee activity at
flowers was significantly higher near apiary sites compared to control sites,
although the mean increase (by a factor of 2.5) was relatively modest. This
increase in honeybees resulted in a significant depression in the availability of
nectar sugar in flowers around apiaries. Hive honeybees appeared to be
excluding feral honeybees from the vicinity of apiary sites. However, there was
little evidence that hive bees caused a decline in the visitation rate or abundance
of native insects, apparently due to very low numbers of native insects and a
superabundance of nectar sugar at some of the sites. However, hive bees may
reduce the number of native insects visiting E. lucida flowers at a subset of
rainforest sites with abundant native insects and low levels of available nectar
sugar.
E. lucida flowers were also depleted of pollen more quickly at apiary sites
compared to control sites, resulting in a 17% reduction in the standing crop of
pollen in male flowers in the vicinity of apiaries. Fruit set tended to be higher
near apiaries, although there was no difference in the number of pollen grains on
stigmas, fruit dehiscence, fruit weight or seed set between apiary and control
sites. Therefore, despite removing pollen more rapidly and reducing the
availability of pollen in male flowers, hive bees appeared to have little net
impact on the reproductive performance of E. lucida trees.

Item Type: Thesis (PhD)
Keywords: Eucryphia, Eucryphia, Honeybee
Copyright Holders: The Author
Copyright Information:

Copyright 2001 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2001. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:41
Last Modified: 17 Nov 2016 22:38
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