Interspecific competition for phosphorus was studied in continuous lake water cultures of phytoplankton communities from Lake Memphremagog, and its outcome shown to depend primarily on the size of the competitors. Comparison of the activity of the inducible enzyme alkaline phosphatase between the lake and cultures operated at various dilution rates (0.06-0.93 day('-1)) established that in situ phosphorus limitation rarely depressed average community growth rates much below 0.6 day('-1). Growth rates under comparable, or even more severe (0.2-0.3 day('-1)) limitation in culture decreased significantly with increasing cell size. Phosphorus uptake kinetics and cell quotas measured by track autoradiography on the competing species showed that biomass and quota-specific uptake rates varied inversely with cell size in highly significant allometric regressions, correctly predicting that competitive outcome should depend on size. Substituted in a variable internal stores model of phosphorus limited growth, the allometric functions for uptake, cell quota, and maximum growth rate correctly predicted observed growth rates except in competition much stronger than natural (D = 0.06-0.2 day('-1)). Failure of the model to encompass cell senescence and death due to severe nutrient stress appeared to account for the discrepancy. Neither the absolute difference in growth rates due to cell size nor the direction of selection among the naturally co-occurring species varied systematically with the intensity of competition, indicating that spatio-temporal variation of limiting phosphorus supply in nature is unlikely to directly select the size or taxonomic composition of phytoplankton communities.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.68623 |
| Date | January 1981 |
| Creators | Smith, Ralph E. H. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biology) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000139598, proquestno: AAINK54918, Theses scanned by UMI/ProQuest. |
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