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The effect of the non-native superb lyrebird (Menura novaehollandiae) on Tasmanian forest ecosystems

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Tassell, S (2014) The effect of the non-native superb lyrebird (Menura novaehollandiae) on Tasmanian forest ecosystems. PhD thesis, University of Tasmania.

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Abstract

Some 900 species of bird have been introduced throughout the world but the research
effort regarding their ecological impact as non-native species has been minimal and
largely based on ad hoc observations. In particular, the impact of non-native birds on
non-avian components of native biota and ecosystem function are poorly understood. I
addressed this knowledge gap by investigating the effect of the non-native superb
lyrebird (Menura novaehollandiae) on native soil- and leaf litter-dwelling forest
invertebrates, seedling survival and ecosystem processes within the wet eucalypt forests
of Tasmania, Australia. The superb lyrebird is a predator of invertebrates and is an
ecosystem engineer capable of turning over hundreds of tonnes of soil and leaf litter per
hectare every year. The absence of any native equivalent-sized predator of invertebrates
or native species capable of such large-scale habitat modification within Tasmanian wet
forest means that the superb lyrebird may have a significant negative effect on
Tasmanian forest ecosystems.
I used a multifactorial approach consisting of field surveys and manipulative
experiments to examine the impact of the superb lyrebirds at a number of spatial and
temporal scales. Firstly, I surveyed six sites, three invaded by lyrebirds and three
without lyrebirds to investigate the patterns of association between macroinvertebrate
assemblage structure and abundance and the presence of superb lyrebirds. I found that
the presence of superb lyrebirds was associated with lower abundance and taxonomic
richness of invertebrates, higher evenness and altered assemblage composition but the
magnitude of this relationship was strongly dependent on small-scale variation in
microhabitat.
To establish any causal link between the presence of lyrebirds and patterns in
invertebrate assemblages and seedling numbers, I conducted two manipulative field
experiments that examined the short and long term influence of superb lyrebird
disturbance. The physical disturbance of soil and leaf litter immediately reduced the
abundance and taxonomic richness of macroinvertebrates, those that inhabit leaf litter
being more affected than generalists and soil dwelling taxa. However, the influence was
short-lived: the abundance of generalist and soil dwelling taxa was similar to that of
individuals in undisturbed areas within 21 days. Similarly, a longer-term experiment found no evidence of impact on invertebrates after approximately two months. Next, I
used a multi-scale survey to determine how the magnitude of the effect of superb
lyrebirds on invertebrate assemblages varied across different spatial scales. While their
effects on invertebrates were profound at small spatial scales and short timeframes, they
were weaker over longer timeframes and at intermediate and landscape scales. In
general, mesoinvertebrates showed a weaker response to the presence of superb
lyrebirds than did macroinvertebrates. Thus, although superb lyrebird scratching causes
obvious changes to the structure of the forest floor of Tasmanian wet eucalypt forests; it
appears that their disturbance is neither frequent nor intense enough to result in lasting
changes in biotic communities. Finally, I tested the influence of superb lyrebirds on
ecosystem function through experiments on the effect of their activity on several
ecosystem processes (decomposition, nitrogen cycling and soil respiration). Superb
lyrebirds increased decomposer potential but did not appear to influence soil respiration
or pH. The concentration of inorganic nitrogen was lower at lyrebird sites; this may
have been linked to their disturbance but the lack of any experimental treatment effects
weakens the strength of this inference. Overall, it is unlikely that the presence of superb
lyrebirds will significantly affect functioning of mature forest ecosystems, as they are
resilient to all but extreme perturbation such as wildfire. This thesis represents an
integrated and holistic examination of the ecological impact of a non-native bird. In
doing so it makes a substantial contribution to global understanding by demonstrating
that non-native birds can have an influence, albeit a limited one in this case, on native
biota and ecosystem function.

Item Type: Thesis (PhD)
Keywords: invasive species, ecosystem engineer, macroinvertebrate, Menura novaehollandiae
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Date Deposited: 10 Nov 2014 00:45
Last Modified: 15 Sep 2017 00:59
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