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Canopy arthropods and herbivory on the Tasmanian southern beeches, Nothofagus cunninghamii and Nothofagus gunnii

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Keble-Williams, PJ (2012) Canopy arthropods and herbivory on the Tasmanian southern beeches, Nothofagus cunninghamii and Nothofagus gunnii. PhD thesis, University of Tasmania.

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Abstract

The Gondwanan relict tree genus Nothofagus has generated much research due to
its biogeographical significance in understanding the biota of the Southern
Temperate Zone. However, the southern temperate forest arthropod fauna, including
that of Nothofagus, has received less attention than northern temperate forest and
tropical rainforest. The extant Tasmanian Nothofagus canopy arthropod fauna has
been considered depauparate. Yet with a palaeohistory of long persistence, high
diversity and widespread distribution of the genus within Australia, the endemic
Tasmanian Nothofagaceae – the evergreen Nothofagus cunninghamii and winter
deciduous N. gunnii - could be expected to have accreted a large and diverse
arthropod fauna, as have its sister Fagalean families in the northern hemisphere.
Conversely, range contraction of Tasmanian Nothofagus in the increasingly arid
conditions of the late Tertiary, and its cyclical isolation from the Australian mainland
during the glacial cycles of the Pleistocene, could have depleted the associated
arthropod fauna.
Thus the aims of this project were to document in detail the diversity and structure
of the invertebrate communities associated with both species of Tasmanian
Nothofagus; to build an inventory of canopy arthropod fauna according to feeding
guild; and to measure the levels of herbivory, as an indication of herbivore activity,
on the these host species. These data enabled comparison of the arthropod
communities on the two hostplants, and comparison with similar studies on closely
related tree species (Nothofagus elsewhere, northern temperate Fagales) and other
Australian tree taxa, now widespread (Acacia and Eucalyptus).
A cross section of survey sites was chosen, 17 for N. cunninghamii, and 12 for N.
gunnii, including three where the host plants were sympatric. Canopy arthropods
were sampled by branch beating, and leaves were collected from, or examined in situ
on marked branches. The sampling schedule from March 1998 until March 2002
yielded data sets by Nothofagus species, site, sampling aspect, season, region, and
between years. Priority was given to arthropod orders containing herbivorous taxa or
scavenging taxa known to forage on trees. These were sorted to family, then genus
and species where possible, otherwise to morphospecies; and allocated to feeding guilds. The leaves were designated ‘chewed’ or ‘intact’ and the leaf area lost from
the chewed leaves was estimated. Mean percentage leaf area loss was calculated as a
measure of herbivory.
The main finding from these investigations was that there existed a strong contrast
in the diversity and taxonomic profile of the arthropod fauna between the two
Nothofagus species. For N. cunninghamii, the associated fauna was relatively rich in
taxa and comparable with other temperate zone trees in both its diversity and guild
structure. Similarly the N. cunninghamii herbivory levels were within the range of
those found on temperate and subtropical tree taxa. N. gunnii in contrast was clearly
depauparate, particularly lacking many important folivorous groups such as
chrysomelid beetles, leaf miners and aphids. However there was, for the two
Nothofagus species, considerable local variation in the arthropod communities and
levels of herbivory - between regions; between sites within a region; and within a
site, seasonal variation and also differences between consecutive sampling years -
insights which have significance for effective biodiversity surveys and conservation
strategies.

Item Type: Thesis (PhD)
Keywords: Northofagus, canopy, arthropods, biodiversity, herbivory, biogeography, Gondwana, TAsmania
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Date Deposited: 17 Aug 2012 04:44
Last Modified: 11 Mar 2016 05:53
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