Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level



Biological Sciences


Frederick W. Spiegel

Committee Member

Steven L. Stephenson

Second Committee Member

Mary Savin

Third Committee Member

Burton H. Bluhm

Fourth Committee Member

Kusum Naithani


Biological sciences, Earth sciences, Amoebae, Biogeography, Carbon, Microbial ecology, Soil


Investigations into the distribution and ecosystem functions of fruiting amoebae revealed that local-scale environmental conditions can largely explain broad biogeographical patterns in species assemblage, the way in which amoeboid predators shape bacterial communities and how this top-down influence may affect global biogeochemical processes in a changing climate. The distribution and assemblage of protosteloid amoebae on the islands of New Zealand and Hawaii did not yield any expected patterns of island biogeography, and conformed to other global regions studied. The strongest predictor of species richness in a given region was sampling effort and these species do not appear to have any extant barriers to global dispersal. It is proposed that morphological adaptations such as tiny resilient spores contribute to their ability to disperse widely. In addition, the role of soil amoebae in stimulating the mineralization of soil nutrients was examined using a series of microcosm experiments. It was confirmed that amoeboid predators are causative for large increases in carbon and nitrogen mineralization but that the magnitude of this effect depends on complex interactions between climate and edaphic variables. In particular, land management practices such as no-till agriculture determine the nature of predator responses to climate change with regard to biogeochemical cycling. Subsequently, soil amoebae were shown to have a strong influence on the composition of bacterial communities. This influence was also dependent on climate factors. The predation-induced changes to bacterial taxa was different when incubation temperatures were increased, suggesting that even if protists are considered in models of nutrient dynamics, the parameters describing their influence on decomposer communities will depend on environmental factors. Future work should focus on testing hypotheses concerning the importance of morphology and anthropogenic vectors to amoebal dispersal and on further quantifying the interaction between a changing environment and predator-mediated control of bacterial communities for a wider range of predator taxa.