Niche character in a temporally varying environment
Nowack, Shane Patrick.
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One of the major goals in the field of ecology is to understand the connection between an organism and its environment. In this thesis both theoretical and empirical approaches were used to investigate the effects of environmental variation on niche structure. A mathematical model was developed to make predictions about the consequences of temporal frequency regime on optimal behavior. Three different time scales of environmental variation were studied: faster than the growth rate, slower than growth rate, and similar to growth rate. The model results predicted that (i) optimal behavior appears to be independent of fast environmental variation, (ii) niche width is largely determined by slow environmental variation, and (iii) biological clocks may have evolved from environmental variations that occur with a frequency that is comparable to the growth rate of the organism. Representatives of the predominant organisms inhabiting the microbial mats found in the effluent channels of Mushroom Spring, Yellowstone National Park, were cultivated, and the growth rates of the isolated strains were measured with respect to light, temperature, and availability of dissolved inorganic carbon. The growth rate measurements suggested that closely-related Synechococcus species with distinct ecological adaptations exist within the Mushroom Spring community, and may explain the genetic diversity found in situ. The results also suggested that the fundamental light niche is interconnected with other environmental parameters, such as temperature and dissolved inorganic carbon availability. To compare the results of the mathematical and microbiological approaches, environmental light data that were collected in the vicinity of Mushroom Spring were incorporated into the mathematical model. The optimal fundamental light niche that was predicted by the model and the measured light niche of one of the cultivated strains exhibited qualitative similarities. Collectively, this interdisciplinary approach has led to the identification of several environmental characteristics that are hypothesized to be important in determining niche structure.