The ecological and evolutionary dynamics of multiple natural enemies

Natural organisms are infected by many different parasites, and how these parasites interact with each other has important ecological and evolutionary implications. This
study is to understand how organisms with different transmission strategies effect the evolution of each other. Parasites that transmit vertically benefit from the host having a high reproductive rate whilst hosts that transmit horizontally are not affected by host reproduction. Some horizontal parasites may reduce host fecundity to benefit
their own replication within the host. Therefore there will be clear conflict between vertically and horizontally transmitted parasites. The evolution of traits such as
vertically transmitted `protection' and `sabotage' are likely to be costly in terms of other life history traits. In the presence of such `trade-offs,' the parasite population will evolve towards the evolutionarily stable strategy (ESS) that balances the costs and benefits of these strategies in response to a horizontally transmitted parasite. The ecology of the interaction
of vertically and horizontally transmitting parasites is also examined. Further to this, field data is used to construct a model of two horizontally transmitting parasites, a pathogen and a parasitoid that occur on the Orkney Isles. We demonstrate how each of them, and both in combination, may have a large effect on resultant dynamics of winter moth, Operophtera brumata, populations.