Natural communities are structured by a complex of direct and indirect species
interactions. It is well recognized theoretically that if these interactions are weak, the entire community is more likely to persist. Several mechanisms can weaken a predator-prey interaction. I studied interference among conspecific predators and heterogeneity at the prey level. Incorporating these mechanisms into realistic functional responses is
required for accurate model predictions at the community level. However, controversy
remains on which dependencies need to be included. Using laboratory microcosms, I was
able to demonstrate moderate predator-dependence in my model system. This effect was present even at low predator densities and after accounting for prey depletion. In separate experiments, I experimentally compared the functional responses of a gape-limited predator feeding on its prey in the absence or presence of species outside the predator's diet (non-prey). I demonstrated that both density and diversity of non-prey species can also substantially reduce the strength of predator-prey interactions. I further tested this non-prey effect on a long time-scale, where I compared the population dynamics of predator and prey alone to the dynamics of predator and prey when a non-prey species was present. Prey and predators had both gone extinct at the end of the experiment for all replicates containing only predator and prey. However, in the treatment that included non-prey, all species persisted in 4 out of the 5 replicates until the last day of the
experiment. Prey species also spent significantly more time above the detection limit in the treatment with non-prey. In addition, I studied how inducible anti-predator defenses affect an aquatic food web with intraguild predation. I detected substantial clonal variation in the expression of a morphological inducible defense and the long-term experiment showed that the intraguild prey with greater ability to increase their body width as a response to predation also have longer persistence times. These results show that predator interference and prey heterogeneity may be important factors that increase
persistence of predator and prey as predicted by theory. Their incorporation into simple food web models can improve our ability to reliably predict community dynamics.
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/2822 |
| Date | 26 May 2010 |
| Creators | Kratina, Pavel |
| 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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