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Evolutionarily stable investment in secondary defences

  1. M. BROOM1,*,
  2. M. P. SPEED2,
  3. G. D. RUXTON3

Article first published online: 27 SEP 2005

DOI: 10.1111/j.1365-2435.2005.01030.x

Issue

Functional Ecology

Functional Ecology

Volume 19, Issue 5, pages 836–843, October 2005

Additional Information

How to Cite

BROOM, M., SPEED, M. P. and RUXTON, G. D. (2005), Evolutionarily stable investment in secondary defences. Functional Ecology, 19: 836–843. doi: 10.1111/j.1365-2435.2005.01030.x

Author Information

  1. 1

    Centre for Statistics and Stochastic Modelling, Department of Mathematics, University of Sussex, Brighton BN1 9RF, UK,

  2. 2

    School of Biological Sciences, University of Liverpool, Liverpool L69 7ZB, UK, and

  3. 3

    Division of Environmental & Evolutionary Biology, Institute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, UK

* †Author to whom correspondence should be addressed. E-mail: M.Broom@sussex.ac.uk

Publication History

  1. Issue published online: 10 OCT 2005
  2. Article first published online: 27 SEP 2005
  3. Received 28 January 2005; revised 10 May 2005; accepted 18 May 2005

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Keywords:

  • Automimicry;
  • Evolutionarily Stable Strategy;
  • levels of defence;
  • mixed strategy;
  • toxins

Summary

  • 1
    Previous workers have suggested that the evolutionarily stable strategy (ESS) for investment in antipredator defences, such as toxins, will critically depend on the nature of expression of the defence. Specifically, it has been suggested that if the different levels of a defence are best described as a continuous variable, then this will lead to pure ESSs with all individuals in a population adopting similar defence levels; whereas defences that can only take on discrete levels will lead to mixed ESSs (featuring variation in defence within the population).
  • 2
    Our principal aim is to determine the validity of these viewpoints, and examine how the pure and mixed strategies predicted by the two types of defences can be reconciled with practical and philosophical difficulties in defining any given defence unambiguously as continuous or discrete.
  • 3
    We present the first model of a continuously varying defence that is solved explicitly for evolutionarily stable strategies.
  • 4
    We are able to demonstrate analytically, that the model always has a unique ESS, which is always pure. This strategy may involve all members of the population adopting no defence, or all members of the population making the same non-zero investment in defence.
  • 5
    We then modify our model to restrict the defence to a number of discrete levels and demonstrate that the unique ESS in this case can be either pure or mixed. We further argue that the mixed ESS can be a combination of no more than two defence levels, and the two levels in a mixed ESS must be nearest neighbour levels in an ordered list of the levels that the defence can take.
  • 6
    This, in turn, means that the mixed ESS will be practically identical to a pure ESS if the discrete defence is fine-grained.
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