Plankton play a key role in regulating nutrient and carbon cycles in freshwater ecosystems. The uptake and processing of nutrients in planktonic biomass are highly sensitive to changes in the environment, such as alterations in the availability of limiting nutrients, increasing temperature due to climate change, and changes to the composition of interacting species. The focus of this thesis is to use a variety of experimental and theoretical methods to assess and predict the impact of multiple perturbations on community structure, dynamics and ecosystem function, with a particular focus on interactions between phytoplankton and their consumers (zooplankton). Increases in both temperature and phytoplankton species diversity independently decreased CO2 concentrations when the number of non-resource species (those inedible to the zooplankton) were high. Using structural equation modeling I show that the effect is indirect, resulting largely from the positive impacts on total biomass of phytoplankton. Phytoplankton are limited by a range of resources, and differences in the functional traits used to utilize light and nutrients can explain the distributions of species under different temperature regimes. I found that under light and nitrogen limitation, resource requirements are generally lowest at intermediate temperatures, and that changes in temperature may therefore alter the competitive hierarchy amongst species. Using the model freshwater phytoplankton Chlamydomonas reinhardtii, I also find that previous selection environments govern future competitive abilities in phytoplankton. Adaptation to a high salt and low nutrient stress increases competitive ability under light limited conditions, indicating a strong dependency of selection environment for overall competitiveness. This thesis provides a mechanistic insight into the role of diverse plankton communities for community dynamics and ecosystem functioning.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:766217 |
| Date | January 2018 |
| Creators | Lewington-Pearce, Leah |
| Publisher | Queen Mary, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://qmro.qmul.ac.uk/xmlui/handle/123456789/44691 |
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