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Title: Modelling the impact of an alien invasion : Harmonia axyridis in Britain
Author: Comont, Richard Francis
ISNI:       0000 0004 5349 9431
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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Harmonia axyridis is a ladybird native to Asia, but introduced widely as a biocontrol agent. It is invasive and detrimental to native species in North America, which meant its arrival in Britain was met with concern. Establishment was seen as an opportunity to track the spread of an invasive alien species (IAS) whilst also monitoring impacts on native species. The aims of this thesis were to examine the responses of native British ladybirds to the arrival of H. axyridis, to establish the effect of the IAS on native ladybirds when compared to other drivers, and to investigate the possible facilitation of the H. axyridis invasion by natural enemy release. Modelling ladybird distributions with life-history and resource-use traits found that species predatory on a wide range of prey families had larger range sizes than those which ate fewer prey types. This suggests that the wide diet breadth of the IAS is likely to have played a critical role in the species’ rapid spread. Dietary niche overlap between H. axyridis and native ladybirds showed positive correlation with declines of native ladybirds. This indicates that the IAS is playing an important role, but the significance of urbanisation suggests habitat destruction is also significant. Abundance of H. axyridis was influenced by habitat type and aphid abundance, but not by the native ladybird community, suggesting the spread of the IAS will not be slowed by biotic resistance. Harmonia axyridis is attacked by native parasitoids, but at a much lower rate than is the native Coccinella septempunctata, in line with natural-enemy release theory. There was no evidence of attack rate increasing with time since arrival in an area. Overall, H. axyridis is an extremely successful IAS, with detrimental effects on native ladybirds which are likely to continue.
Supervisor: Roy, Helen E.; Purse, Bethan V.; Lewis, Owen T.; Harrington, Richard; Shortall, Chris T. Sponsor: Natural Environmental Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biology ; Life Sciences ; Biodiversity ; Zoological sciences ; Ecology (zoology) ; Biology and other natural sciences (mathematics) ; Biotic resistance ; Climate ; Coccinellidae ; Coleoptera ; Colonisation ; Community ; Diet breadth ; Distribution ; Enemy release hypothesis ; Extinction ; Great Britain ; Habitat ; Harmonia axyridis ; Invasive alien species ; Native species ; Natural enemies ; Niche breadth ; Niche overlap ; Range fill ; Range size ; Traits