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Group 6
Inducible defences in intraguild predation systems
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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. 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.
Normal and induced morphs of Euplotes octocarinatus. Scale bar is 40 microns. Figure taken from here.
The goal of this assigment is to study the effects of inducible defences on the dynamics of intraguild predation.
Fig. 1. The intraguild predation community module.
Intraguild predation is one of the basic three species community modules. 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).
Assignment
Develop an ordinary differential equations model for intraguild predation that takes into account inducible defences on the intraguild prey. Can you show that inducible defences enhance the persistence of the intraguild prey? What are the conditions or parameter values to allow persistence?
Extension
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?