Evol Ecol Res 14: 125-146 (2012)     Full PDF if your library subscribes.

Evolution of host resistance towards pathogen exclusion: the role of predators

Andy Hoyle1, Alex Best2,3 and Roger G. Bowers4

1School of Natural Sciences, University of Stirling, Stirling, UK,  2School of Mathematics and Statistics, University of Sheffield, Sheffield, UK,  3Biosciences, College of Life and Environmental Sciences, University of Exeter, Cornwall Campus, Penryn, UK and  4Department of Mathematical Sciences, The University of Liverpool, Liverpool, UK

Correspondence: A. Best, School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH, UK.
e-mail: a.best@shef.ac.uk


Question: Can increased host resistance drive a pathogen to extinction? Do more complex ecosystems lead to significantly different evolutionary behaviour and new potential extinctions?

Mathematical method: Merging host–parasite models with predator–prey models. Analytically studying evolution using adaptive dynamics and trade-off and invasion plots, and carrying out numerical simulations.

Key assumptions: Mass action (general mixing). All individuals of a given phenotype are identical. Only prey vulnerable to infection. Mutations are small and rare (however, the assumption on the size of mutation is relaxed later). In simulations, very small (negligible) populations are at risk of extinction.

Conclusions: The presence of the predator can significantly change evolutionary outcomes for host resistance to a pathogen and can create branching points where none occurred previously. The pathogen (and sometimes the predator) is protected from exclusion if we take mutations to be arbitrarily small; however, relaxing the assumption on mutation size can lead to its exclusion. Increased resistance can drive the predator and/or pathogen to extinction depending on inter-species dynamics, such as the predator’s preference for infected prey. Predator co-evolution can move exclusion boundaries and prevent the predator’s own extinction if its rate of mutation is high enough (with respect to that of the prey).

Keywords: adaptive dynamics, co-evolution, eco-epidemiology, extinction, parasite, singular strategy.

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