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Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 69-75).

Thesis--Wisconsin. / Vita. Includes bibliographical references.

This thesis investigates the effect of resource recovery delays, both continuous and discrete, on the behaviour and population dynamics of harvested predator-prey systems. Three models were tested with respect to local stability, global stability, and state-space trajectories. The method of D-partitions was used to determine local stability properties while simulations were performed to discover global properties. Generally, delays were found to induce multiple transitions between locally stable and unstable equilibria as harvest rates are changed. This phenomenon occurred under the management strategies of constant-effort harvesting and constant-quota stocking and harvesting. In addition, in the predator-prey models with delay, a high conversion efficiency and a high satiation limit for the predators can effect instability; this is not possible without delays. Global investigations confirmed the local results and extended them to the simultaneous harvesting of the predator and prey for constant-quota harvesting and stocking. The simulations also showed bifurcations in limit cycles as the carrying capacity was altered and as the stocking rates were varied. Nutrient-limited phytoplankton cultures in chemostats were analyzed with the mathematical techniques. It is shown that multiple stability transitions with changes in dilution rates are theoretically possible but observed delays are not large enough to produce this behaviour. / Graduate and Postdoctoral Studies / Graduate

This study aimed to better understand the role of rodents as seed predators and dispersers in the fynbos biome at De Hoop Nature Reserve, South Africa in May and June, 2013. Based on previous studies I hypothesised that the large, nut-like seeds of Ceratocaryum argenteum (Restionaceae) are scatter-hoarded by rodents and that rodent seed choices and seed fates are affected by seed size and hull thickness. Field trials using three seed types showed that smaller seeds with a high reward and low processing cost were consumed significantly(p<0.01) more than large, thick hulled seeds. Application of wire tags to facilitate discovery of relocated seeds had no significant influence on seed choice (p>0.05), but further research should be conducted to determine if spooling of C. argenteum seeds influences rodent seed choice. Smaller seeds with a high-reward and low processing cost showed a significantly greater percentage of usage (p<0.01) where seed stations were encountered and exploited. Rhabdomys pumilio was confirmed as being the most common murid at the study site, however, it seems unlikely that it scatter-hoards C. argenteum seeds, as no consumption or burial of seeds was observed. However, R. pumilio did show an interest in C. argenteum seeds and attempted to consume some seeds or carried seeds over distances not significantly different (p>0.05) from the observed distances between nearest neighbour C.argenteum plants before discarding them on the soil. Additionally, the maximum distance R. pumilio moved C. argenteum seeds was commensurate with the maximum distance between nearest neighbour C. argenteum stands, so the end fate of the seeds remains unknown. Further research should account for seasonal variability in scatter-hoarding behaviour.

Intraguild (IG) predation, where species within the same guild prey on each other, is common in aquatic communities. I used the abundance and distributional patterns of three species of Rhyacophila (Trichoptera), derived from a survey of 25 streams in Nova Scotia, Canada, to test several predictions of IG theory. I first sampled microhabitats and conducted behavioural observations to establish that the species do co-occur and prey on each other. Abundance patterns did not conform to two key model predictions: (1) Neither of the IG prey (R. minor, R. vibox) was excluded from the most productive streams, and (2) IG prey densities were not inversely related to productivity in streams with the IG predator (R. fuscula). It remains possible that intraguild predation occurs between these species of Rhyacophilia, the measured abundances do not indicate any measurable effects from IGP, the abundance being determined instead by the availability of prey.

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