[{"key":"dc.contributor.author","value":"Bell, Thomas","language":null},{"key":"dc.date.accessioned","value":"2009-08-04T21:29:49Z","language":null},{"key":"dc.date.available","value":"2009-08-04T21:29:49Z","language":null},{"key":"dc.date.issued","value":"2001","language":null},{"key":"dc.identifier.uri","value":"http:\/\/hdl.handle.net\/2429\/11632","language":null},{"key":"dc.description.abstract","value":"The two experiments described in this thesis attempt to identify the mechanisms\r\nthat determine the biomass of trophic levels in freshwater communities. Early work in\r\nthis field suggested that trophic level biomass is determined by resource supply and levels\r\nof predation. I present the results of two studies that investigate the impact of various\r\nother factors on the biomass of trophic levels. In the first study, I describe the short-term\r\nimpact of prey (phytoplankton) edibility on the phytoplankton response to nutrient\r\nenrichment and the addition of a top (third) trophic level. The results suggest that the\r\nproportion of inedible phytoplankton in the community modifies the degree to which\r\nphytoplankton biomass is regulated by bottom-up (nutrient supply) or top-down\r\n(predation) forces. Compensation by inedible phytoplankton could therefore preclude the\r\npropagation of top-down signals in these communities. As a result, experiments over\r\nlonger time scales might show a progressive weakening of top-down signals. In the\r\nsecond study, I therefore describe the results of a long-term (4-year) experiment in which\r\nzooplanktivorous fish are either present or absent. The results of this experiment,\r\ncombined with the results of an extensive literature analysis, provide evidence that there\r\nis in fact no obvious decline in the strength of top-down signals with increasing\r\nexperiment duration. The results do suggest, however, that the experimental results\r\ndepend to some degree on the type of system in which the study is performed.","language":"en"},{"key":"dc.format.extent","value":"3199518 bytes","language":null},{"key":"dc.format.mimetype","value":"application\/pdf","language":null},{"key":"dc.language.iso","value":"eng","language":"en"},{"key":"dc.publisher","value":"University of British Columbia","language":null},{"key":"dc.rights","value":"For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https:\/\/open.library.ubc.ca\/terms_of_use.","language":null},{"key":"dc.title","value":"The propagation of top-down and bottom-up signals in heterogeneous aquatic food webs","language":"en"},{"key":"dc.type","value":"Text","language":null},{"key":"dc.degree.name","value":"Master of Science - MSc","language":"en"},{"key":"dc.degree.discipline","value":"Zoology","language":"en"},{"key":"dc.degree.grantor","value":"University of British Columbia","language":null},{"key":"dc.date.graduation","value":"2001-11","language":"en"},{"key":"dc.type.text","value":"Thesis\/Dissertation","language":"en"},{"key":"dc.description.affiliation","value":"Science, Faculty of","language":null},{"key":"dc.description.affiliation","value":"Zoology, Department of","language":null},{"key":"dc.degree.campus","value":"UBCV","language":"en"},{"key":"dc.description.scholarlevel","value":"Graduate","language":"en"}]