| Summary: | Saxicolous lichens on exposed bedrock are subjected to desiccation stress and intense light levels. Members of the genera Xanthoparmelia and Arctoparmelia are common foliose lichens on the Precambrian Shield, produce abundant sexual structures, and form part of the bedrock communities. The general goal of this thesis was to better understand the influence of community and underlying geology on three saxicolous lichens: Arctoparmelia centrifuga, Xanthoparmelia viriduloumbrina and X. cumberlandia. More specific goals were further examined in five chapters to investigate: 1) life history strategies of the three species, 2) a trade-off between fecundity and fungal secondary metabolite production; 3) an effect of substratum element composition on previously defined communities and lichen biology, 4) substratum preferences of Xanthoparmelia species, and 5) the photobiont guild hypothesis of the three species in a preliminary study. Field collections of lichens and environmental data were made in four locations on the Precambrian Shield in Manitoba and Ontario. Secondary metabolites were determined by digitally enhanced thin-layer chromatography. Fecundity was measured by number of apothecia, ascospores, and percent germination. Elements in rock samples were quantified by aqua-regia digest and inductively coupled plasma optical emission spectroscopy analysis and light microscopy was used to observe and quantify fungal germination and growth. The results showed eighty-one lichen species comprising three lichen communities; mossy rock, grassy rock, and treed rock communities. Lichen communities and fecundity were used to characterize life history strategies as competitive for Arctoparmelia centrifuga, stress tolerant for Xanthoparmelia viriduloumbrina, and ruderal generalist for Xanthoparmelia cumberlandia. A potential trade-off was reported for X. cumberlandia between sexual fecundity and a secondary metabolite. Substratum preferences were found at the genus level and element differences at the species level. Experimental evidence further supported geological preferences for the three species. Finally, the photobiont guild hypothesis could not be supported by this preliminary work. This research provides a broad overview of ecological and biological patterns found in Arctoparmelia and Xanthoparmelia species. The research forms a foundation for further studies in substratum preference and life history characterization in lichens. It can be further applied to habitat suitability modelling which may be valuable for phylogenetic context or in conservation biology of lichens. === October 2015
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