Date of Award


Degree Name

MS in Biological Sciences


Biological Sciences


College of Agriculture, Food, and Environmental Sciences


Nishanta Rajakaruna

Advisor Department

Biological Sciences

Advisor College

College of Agriculture, Food, and Environmental Sciences


Lichens are among the most prominent and successful life forms of metal-rich habitats, including ultramafic rocks and soils; however, research on lichens of ultramafic habitats is limited, especially on the North American continent. A review of the published literature on lichens of ultramafic substrates in North America yielded a total of 437 lichen species reported from ultramafic rocks and soils. Lichen assemblages of ultramafic substrates vary in composition and are dominated by acidophytic (low pH preferring) taxa with a minor, but consistent, basiphytic (high pH preferring) component. Species lists from ultramafic habitats in different geographic regions varied widely, suggesting that factors unrelated to substrate, such as climate, have a large effect on lichen assemblage composition. However, several studies showed clear differentiation between lichen composition on nearby or adjacent ultramafic and nonultramafic habitats, suggesting that ultramafic substrates harbor regionally unique lichen assemblages. In a regional community ecology study, we sampled lichen biotas of eight ultramafic and eight sandstone outcrops along a 70 km maritime influence gradient in order to test three hypotheses: 1) a substrate effect hypothesis that saxicolous lichen communities of ultramafic and sandstone outcrops are compositionally distinct; 2) a maritime gradient hypothesis that coastal and inland communities are compositionally distinct; and 3) a maritime moderation hypothesis that coastal ultramafic and sandstone communities are more similar than those of inland ultramafic and sandstone. Relationships between lichen communities and abiotic variables were analyzed using perMANOVA. Ultramafic communities showed significant differentiation from sandstone communities in the study area. A total of 134 taxa were recorded - 81 taxa from ultramafic outcrops and 100 taxa from sandstone, with 47 taxa found on both rock types. Ultramafic outcrops were characterized by greater similarity between samples, lower lichen cover, larger differences in cover between north and south aspects, and higher abundance and diversity of cyanolichen taxa relative to sandstone. Coastal, intermediate, and inland communities were compositionally distinct from one another, and sandstone and ultramafic assemblages were significantly differentiated in all coastal distance groups. This study is one of few to quantitatively examine lichen communities of two rock types, and is unique in that it does so at a regional scale. These results add to our understanding of the interactive roles of substrate and maritime influence in lichen community assembly.