The studies described in this thesis investigate the role of indirect effects in invasion biology. The Introduction provides a brief overview of indirect effects and an outline of the thesis structure. The role of indirect effects in the context of invasion biology is addressed in an in-depth published literature review that comprises the second chapter, providing a theoretical background for the subsequent empirical studies. Chapters Three to Six are comprised of manuscripts that have been published or are under review or in press, which describe studies that investigate the importance of indirect effects in invasion biology using a model system consisting of the alien Asteraceae Senecio madagascariensis, a closelyrelated native, Senecio pinnatifolius, and the insect species with which they interact. Senecio madagascariensis and S. pinnatifolius occur in a similar geographic range in eastern Australia and these studies were conducted in mixed and pure populations of the two species. The herbivore and floral visitor assemblages of the two Senecio species at seven field sites in South-east Queensland were compared using sweep-net sampling, manual searching and floral visitor observation techniques. The floral visitor assemblages were similar between the two species, comprised largely of species of Syrphidae and the European honeybee, Apis mellifera. Herbivore assemblages, however, were highly variable both between species and between sites, with greater herbivore abundance and diversity recorded on the native S. pinnatifolius than its alien congener. The most commonly recorded herbivores were sap-sucking species such as Myridae. The magpie moth, Nyctemera amica was the most common folivore on both Senecio species and laboratory studies demonstrated a clear preference by ovipositing females and feeding larvae of this species for the native Senecio species, over the alien. Field surveys supported these findings, recording greater leaf damage on the native species than the invader. Herbivory levels were lower, rather than higher, in mixed populations than in pure populations, thus there was no evidence that the presence of one species enhanced herbivory in the other. Field pollination trials were conducted to determine whether competition for pollinators or facilitation of pollination occurred in mixed Senecio populations. The presence of the native S. pinnatifolius affected pollinator visitation rates to the alien Senecio; bee visits to S. madagascariensis were significantly reduced by the presence of S. pinnatifolius, whilst syrphid visits increased. However, altered visitation rates were not reflected in seed set. The presence of the alien species had no impact on pollinator visits to the native. Surprisingly, S. pinnatifolius seed set was higher in mixed populations than in pure populations. This might be due to abiotic factors, lower rates of herbivory at these sites or transfer of pollen between species resulting in the production of hybrid seed (if S. madagascariensis has greater male fitness). Hybridisation in the field was investigated using AFLP techniques. No mature hybrid plants were recorded in mixed populations, but hybrid seeds were produced by both species. Senecio pinnatifolius maternal parents produced higher numbers of hybrid seed than expected based on the relative frequencies of the two species, whilst hybridisation in S. madagascariensis was lower than expected. This may indicate greater male fitness of the invader. A range of complex indirect interactions can occur between invasive and native species, with these interactions having the potential to influence the success or failure of the invader and its impacts on co-occurring natives. The Discussion addresses the findings of the studies described here in the context of invasion biology theory.

Submitted by Cássia Santos (cassia.bcufg@gmail.com) on 2015-10-26T13:53:50Z No. of bitstreams: 2 Dissertação - Paola Arielle Ferreira Nobre - 2015.pdf: 2865061 bytes, checksum: eb60843824dc4bc74edc88795332bc18 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-10-26T14:09:22Z (GMT) No. of bitstreams: 2 Dissertação - Paola Arielle Ferreira Nobre - 2015.pdf: 2865061 bytes, checksum: eb60843824dc4bc74edc88795332bc18 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-10-26T14:09:22Z (GMT). No. of bitstreams: 2 Dissertação - Paola Arielle Ferreira Nobre - 2015.pdf: 2865061 bytes, checksum: eb60843824dc4bc74edc88795332bc18 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-03-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / the factors that influence the choice of egg-laying sites by adult insects is critical in order to identify the major drivers of host-plant use by insects. The abundance of different plant species and the level of feeding specialization of insects have been considered as determinants of the preferential use of host-plants by herbivorous insects. We analyzed the host use patterns of endophagous insects that feed on Asteraceae flower-heads to test the following hypotheses: (i) the abundance of a plant species has a positive effect on the preference of herbivorous insects for that plant species, and (ii) the relative importance of plant abundance in determining preferential use is greater for herbivorous species that use a wider range of host-plant species. We used data on the interactions between herbivorous insects and Asteraceae host-plants family sampled in 20 Cerrado areas in São Paulo State. We analyzed 11 species of endophagous insects and 12 host-plant species. For eight species of herbivorous insects, plant species abundance showed a positive influence on herbivore preference. Three insect species did not respond to any influence of plant abundance on feeding preferences, but one of them showed a positive effect of plant species identity. Furthermore, both the most specialized and the most generalist insect species presented a stronger positive effect of plant species abundance in their choice of a host-plant. Therefore, our study shows that the abundance of plant species is a major factor determining the preferential use of hostplants by the endophagous insects of Asteraceae. Moreover, we show that herbivore diet breadth mediates the relationship between host use and plant abundance. / Estudos abordando interações entre insetos herbívoros e plantas hospedeiras abrangem uma vasta gama de aspectos ecológicos. Boa parte desses aspectos pode ser relacionada diretamente ou indiretamente com a alta dependência que os herbívoros apresentam em relação às suas plantas hospedeiras. Devido a essa alta dependência os insetos herbívoros respondem tanto à riqueza e densidade, quanto ao arranjo espacial das hospedeiras no habitat (Wright and Samways 1999, Summerville and Crist 2001, Tsharntke and Brandl 2004). Além das plantas hospedeiras proporcionarem recurso alimentar para os insetos, elas também fornecem abrigo e microclima adequado para o desenvolvimento dos imaturos (Gaston et al. 1992). Insetos herbívoros não consomem indiscriminadamente as plantas, havendo geralmente alguma preferência por poucas espécies de plantas hospedeiras (Futuyma and Gould 1979). Assim, mudanças, por exemplo, em aspectos quantitativo e qualitativo, nessas hospedeiras podem ter grandes efeitos sobre as populações desses herbívoros. Nesse contexto, pode-se dizer que a amplitude da dieta é um componente fundamental do nicho das espécies de insetos herbívoros, influenciando desde sua dinâmica populacional e suscetibilidade à extinção (Brown 1984), até sua distribuição geográfica (Strong et al. 1984).