Inducible defenses alter the strength of interaction in food webs. Theoretical models that incorporate their effects are therefore critical for predicting community dynamics and stability. I examined ecological effects of an inducible morphological defense in a microbial model. I first investigated the effect of genotype. number of predators, and previous exposure to predators on the speed and maximum level of defense for eight clones in three species of the ciliate Euplotes. The effectiveness of defense depends on both of these aspects of defense induction: therefore these traits should evolve in concert. The speed and maximum level of induction varied among genotypes, showing that there is genetic variance for these traits and the potential for evolutionary change under selection. Higher predator densities led to more rapid induction and higher maximum levels of defense. but previous exposure to predators had no detectable effect on either of these traits. I then used a model selection approach to determine the shape of the functional response of clones that differed in their level of defense, and to estimate and compare the model parameters attack rate and handling time. Defense decreased the attack rate of Euploes on Chlorella vulgar-is algae in one highly defended clone, but did not affect the functional response in two less defended clones. My results demonstrate that Euploes ciliates can precisely and rapidly adjust their morphological defense to the magnitude of predation risk in a way that varies among genotypes. This variation will lead to diversity in prey vulnerability to predators under natural conditions and translates to genetically-based differences in the foraging impact on resources of Euplotes. These estimates of ecological effects of induced defense in this system allow their inclusion in the development and testing of dynamic models. This in turn will inform our understanding of the influence of induced defenses and related trait-mediated indirect effects on community dynamics and stability.
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/1743 |
| Date | 09 September 2009 |
| Creators | Duquette, Shelly |
| Contributors | Anholt, Bradley Ralph |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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