Inducible defenses: continuous reaction norms or threshold traits?
Thomas Owens Svennungsen1, Øistein Haugsten Holen, Olof Leimar
1Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, Blindern, N-0316 Oslo, Norway. t.o.svennungsen@bio.uio.no
The American Naturalist
|August 11, 2011
Summary
Evolutionary models show that prey defense strategies can be continuous or threshold-based. The trade-off curve and disruptive selection favor threshold traits, influencing phenotypic plasticity.
Area of Science:
- Evolutionary biology
- Ecology
- Theoretical biology
Background:
- Phenotypic plasticity allows organisms to adjust traits in response to environmental changes.
- Plastic traits can manifest as continuous reaction norms or discrete threshold traits.
- Selective pressures favoring continuous versus threshold traits remain poorly understood.
Purpose of the Study:
- To investigate the evolutionary conditions favoring continuous reaction norms versus threshold traits in prey defense strategies.
- To model how trade-offs and predator-prey dynamics influence the evolution of phenotypic plasticity.
Main Methods:
- Developed a mathematical model of prey defense induction.
- Incorporated cues of predator density, defense-fecundity trade-offs, and predator-prey feedback loops.
- Analyzed evolutionarily stable strategies for defense induction.
Main Results:
- Both continuous reaction norms and threshold traits can be evolutionarily stable solutions.
- The shape of the defense-fecundity trade-off curve is critical in determining the outcome.
- Disruptive selection and dimorphism-favoring conditions promote threshold traits, especially with informative cues.
Conclusions:
- The type of phenotypic plasticity (continuous vs. threshold) depends on specific selective and ecological conditions.
- Threshold traits are favored under disruptive selection and when ecological conditions promote defense dimorphism.
- Observational data may obscure the underlying reaction norm type, necessitating careful interpretation.
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