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The population biology of two sympatric alien gallwasps and their recruitment of natural enemies

Townsend, Ian. 2013 The population biology of two sympatric alien gallwasps and their recruitment of natural enemies. Reading University, School of Biological Sciences, PhD Thesis.

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Abstract/Summary

There remain many unaddressed questions in both population biology and community ecology. For instance, there are gaps in our understanding of the population dynamics of complex life-cycles, certain life history strategies under variable environments, interactions between newly resident species (e.g. alien species etc.) and communities. In this thesis I address some of these open questions using two species of cynipid gallwasps, the species Andricus quercuscalicis (Burgsdorf, 1783) (Hymenoptera: Cynipidae) and A. grossulariae (Giraud, 1859), as a model system. Cynipid gallwasps offer a range of appropriate and convenient characteristics that make them a suitable but tractable study system. The four chapters in this thesis open with a range of questions, both specific to the chosen gall wasp system and of wider ecological interest. The first two chapters are address questions about the population biology and community ecology of the gallers and their parasitoid enemies. Chapters 3 and 4 take a theoretical approach, in the form of population models, to ask questions that have arisen from the complex life-cycles of the two galler species. In Chapter 2, The population biology of two niche sharing alien gallwasps, I present analyses using data from extensive rearings of galls for both A. quercuscalicis, and the newer resident alien A. grossulariae to gain a theoretical understanding of the population biology of the two species. I also ask questions regarding the extent of any interactions the two species may have. In Chapter 3, Native parasitoid communities and their interactions with invasive gallwasp hosts, I record the communities of parasitoids that attack both hosts and compare these to historical studies. I also examine patterns of spatial density dependence and the sex ratios of parasitoid species. The chapter is the first study to consider the associated parasitoid communities of both hosts together since the arrival of A. grossulariae in the British Isles. In Chapter 4, The Population Dynamics of a Complex Life-cycle, I derive and analyse a single species population model tailored specifically for the complex, non-overlapping, alternate generation life-cycles of A. quercuscalicis and A. grossulariae. I examine the range of dynamical behaviours displayed by these complex life-cycles and how these dynamics change under the influence of exogenous factors. I also use the model to explore generalities outside of the specific gall wasp system. In Chapter 5, Optimum Diapause Strategies Under Different Forms of Environmental Variability, I derive and analyse a general population model incorporating different types of environmental variation, both deterministic and stochastic. I explain how optimal diapause strategies can mitigate against environmental variability and how changes in strategies compare subject to stochastic environment types.

Item Type: Publication - Thesis (PhD)
Programmes: CEH Topics & Objectives 2009 - 2012 > Biodiversity > BD Topic 2 - Ecological Processes in the Environment > BD - 2.2 - Quantify the impact of invasive species, pathogens ...
CEH Sections: Pywell
NORA Subject Terms: Ecology and Environment
Date made live: 31 Mar 2014 13:09 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/506444

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