Interactions Among Leaf Miners, Host Plants and Parasitoids in Australian Subtropical Rainforest
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Food Webs along Elevational Gradients: Interactions among Leaf Miners, Host Plants and Parasitoids in Australian Subtropical Rainforest Author Maunsell, Sarah Published 2014 Thesis Type Thesis (PhD Doctorate) School Griffith School of Environment DOI https://doi.org/10.25904/1912/3017 Copyright Statement The author owns the copyright in this thesis, unless stated otherwise. Downloaded from http://hdl.handle.net/10072/368145 Griffith Research Online https://research-repository.griffith.edu.au Food webs along elevational gradients: interactions among leaf miners, host plants and parasitoids in Australian subtropical rainforest Sarah Maunsell BSc (Hons) Griffith School of Environment Science, Environment, Engineering and Technology Griffith University Submitted in fulfilment of the requirements of the degree of Doctor of Philosophy February 2014 Synopsis Gradients in elevation are used to understand how species respond to changes in local climatic conditions and are therefore a powerful tool for predicting how mountain ecosystems may respond to climate change. While many studies have shown elevational patterns in species richness and species turnover, little is known about how multi- species interactions respond to elevation. An understanding of how species interactions are affected by current clines in climate is imperative if we are to make predictions about how ecosystem function and stability will be affected by climate change. This challenge has been addressed here by focussing on a set of intimately interacting species: leaf-mining insects, their host plants and their parasitoid predators. Herbivorous insects, including leaf miners, and their host plants and parasitoids interact in diverse and complex ways, but relatively little is known about how the nature and strengths of these interactions change along climatic gradients. In order to determine how elevational changes in climatic conditions affect interactions among leaf miners, their host plants and their parasitoids, I quantified these communities and their interactions along three elevational gradients in eastern Australian subtropical rainforest. In doing so, I aimed to 1) provide information on host plant use of leaf miners and the elevational associations of these relationships, 2) understand how the species richness and assemblage composition leaf miners and their parasitoids, and composition of interactions with their hosts (plants or leaf miners), is affected by elevation, 3) uncover any elevational changes in the structure of quantitative networks connecting leaf miners and their parasitoids, and 4) test if parasitism pressure increases at the lower edge of, and below the elevational range of a specific leaf miner species. Information on leaf miners, their host plants and parasitoids was obtained by hand- collecting active leaf mines at sites situated along three gradients, encompassing elevations ranging from 262 -1159m above sea level (a.s.l.), over a twelve month period. Mines were reared into adult leaf miners or parasitoids, which were identified to species or morphospecies. Following this, I carried out an experiment to test if parasitism pressure on a species of leaf-mining weevil was greater at lower, warmer elevations. i This research has provided a large amount of information on an insect guild that is relatively understudied in Australia. In terms of abundance, high elevation sites tended to be dominated by leaf miners that have a higher degree of host specificity, whereas the proportion of generalists tended to be higher at lower elevations. Three leaf miner species were identified as being particularly vulnerable to local coextinction as a result of their high host specificity and current restriction to high elevations. While leaf miners and parasitoids responded similarly to elevation in terms of species richness and number of different pairwise trophic interactions, this did not translate to assemblage-level similarities. Assemblage composition of leaf miners and their interaction composition with their host plants showed a strong elevational signal. On the other hand, there was no clear response in assemblages of parasitoids or their interaction composition with hosts. This indicates that that the response of parasitoids to climate change may be less predictable than for leaf miners. My results provide strong evidence that elevation affects quantitative, host-parasitoid food web structure. Climate change may therefore potentially lead to a restructuring of these food webs. Specifically, with increasing elevation, each parastioid species attacked fewer host species (decreasing generality) and each host was attacked by fewer parasitoid species (decreasing vulnerability), and consequently, energy flows were increasingly concentrated around single pairs of interactions (decreasing interaction evenness). In additional, several relatively abundant species of leaf miner appeared to be avoiding parasitism at higher elevations. Little evidence was found that the leaf-mining weevil, Platynotocis sp. (Curculionidae) experienced increased parasitism at lower, compared with higher, elevations. This suggests that this species may not be escaping parasitism as a result of its restriction to higher elevations, but due to other reasons, such as temporal escape from parasitoids, or because parasitoids may not be attracted to the leaf miner. Alternatively, the experimental protocol may not have allowed sufficient opportunity for parasitism and additional studies will confirm this. My research has demonstrated that interactions occurring among leaf miners, their host plants and parasitoids change along elevational gradients in Australian subtropical rainforest. In doing so, I have addressed a major gap in Australian and global biodiversity and climate change research. ii Statement of originality This worhas not previously been submitted for a degree or diploma in any university. To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made in the thesis itself. Sarah Maunsell iii Table of Contents Synopsis………………………………………………………………………………….i Statement of originality……………………………………………………………….iii Table of contents…………………………………………………………………...…..iv List of figures…………………………………………………………………….……vii List of tables………………………………………………………………………...…..x List of colour plates…………………………………………………………………..xiii Journal articles arising from this thesis…………………………………………….xiv Acknowledgements…………………………………………………………..………..xv Chapter 1 Introduction, aims and thesis outline..........................................................1 1.1 Introduction....................................................................................................1 1.2 Aims...............................................................................................................2 1.3 Thesis structure...............................................................................................3 Chapter 2 Literature Review: Leaf miner food webs, elevation and potential impacts of climate change...............................................................................................5 2.1 Introduction....................................................................................................5 2.2 Leaf mining insects and their parasitoids.......................................................6 2.3 Food webs.....................................................................................................10 2.4 Climate change.............................................................................................13 2.5 Summary.......................................................................................................21 Chapter 3 General methods..........................................................................................22 3.1 Introduction..................................................................................................22 3.2 Study region..................................................................................................22 3.3 IBISCA Queensland.....................................................................................25 iv 3.4 Study design and sampling...........................................................................26 3.5 Insect identification......................................................................................32 3.6 Data preparation and analysis.......................................................................32 3.7 Elevational changes in microclimate............................................................32 3.8 Translocation experiment.............................................................................36 3.9 Research permits..........................................................................................36 S3 Supplementary Material................................................................................37 Chapter 4 Leaf miner host plant use and elevation in Australian subtropical rainforest........................................................................................................................40 4.1 Abstract........................................................................................................40 4.2 Introduction..................................................................................................41 4.3 Methods........................................................................................................43 4.4 Results..........................................................................................................45