**Group 6**

====== Too big to gobble: inducible defences in intraguild predation systems ======

Wiki site of the practical exercise of the [[http://www.ictp-saifr.org/mathbio7|VII Southern-Summer School on Mathematical Biology]].

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===== Introduction =====

When predation risk is high, many prey species employ defence mechanisms that potentially reduce their chances of being consumed. These mechanisms can involve shifts in the morphology, physiology, life-history and/or behaviour of prey species. These so-called //inducible defences// can have major effects on the dynamics of interacting species.

Kratina et al. (2010) studied the dynamics of an experimental food web consisting of the unicellular algae //Rhodomonas minuta// which is consumed by both the turbelarian flatworm, //Stenostomum virginianum//, and hypotrich ciliates of the genus //Euplotes// spp., while the latter is also eaten by the turbelarian flatworm.
{{:2018:groups:g6:euplotes.jpg?380 | }} 
The presence of predatory flatworms induces a change in morphology of //Euplotes//, considerably increasing its size. These defended altered forms then have a reduced risk of being eaten by the gape-limited predators. By selecting //Euplotes// clones with high and low inducibility the authors show that inducible defences enhance persistence of //Euplotes// in this system.

//Figure: Normal and induced morphs of //Euplotes octocarinatus//. Scale bar is 40 microns. Figure taken from [[http://web.uvic.ca/~banholt/anhlabsite/id.html|here]]. //


{{ :2018:groups:g6:intraguild_predation.png?240}}
This system is an instance of one of the basic three-species community modules: //intraguild predation//. It is composed of two consumers that share a common resource and one of the consumers (the intraguild predator) can prey on its competitor (the intraguild prey) - see figure. One of the challenges of these systems is to find robust conditions for persistence of all three species - they are ubiquitous in nature, but are usually restricted to narrow parameter ranges in models!


===== Assignment =====

Develop and analyze a model for the population dynamics of the system described, taking into account inducible defences of the //Euplotes// prey, and use it to explore the consequences of this defence mechanism.

===== Questions and suggestions =====
  * Do inducible defences enhance the persistence of the intraguild prey? What are the conditions or parameter values that allow persistence?
  * It is quite reasonable to assume that induced morphs individuals might have a decreased foraging efficiency, as pointed out in Kratina et al (2010). What are the effects of this trade-off in the dynamics?
==== Challenge ====
  * Inducible defences are not free: they incur extra developmental costs. Assuming a small cost, is it advantageous to have these defences? That is, could it be better to be always small or always big? Under what circumstances?

===== Reference =====
[[http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2656.2010.01705.x/full|Kratina, P., Hammill, E. and Anholt, B. (2010), Stronger inducible defences enhance persistence of intraguild prey. Journal of Animal Ecology, 79: 993–999. doi: 10.1111/j.1365-2656.2010.01705.x
]]