Photogrammetric Exploration of Demographic Change in Juvenile Rhizocarpon geographicum Thalli
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Lichens, although ubiquitous and morphologically diverse, are one group of organisms that remains under-represented in life history and demographic studies, especially in early years. A photographic time series and image analysis were used to identify, track, and quantify morphological and demographic changes of the smallest, observable Rhizocarpon geographicum cohorts over a four-year period (2009 to 2013) at Illecillewaet Glacier, BC. Two objectives were examined: (a) quantify mortality, recruitment, and survivorship, and (b) examine trends correlated with thallus survival and visual, morphological changes in areole formation. Two general predictions were tested: (a) thallus survivorship is positively correlated with average areole area, and (b) there is a linear increase in the number of areoles per year per thallus. Results revealed age-specific mortality was highly variable among different years (8 to 44%), and recruitment occurred in every year. Thallus coalescence was found in every cohort and gradually increased over time. Results also showed that thalli that coalesced had a higher survivorship than solitary thalli. Survivorship was independent of areole area, and areole accumulation did not increase linearly in the number of areoles per year. Overall, this study demonstrates the use of a photographic time series to track and examine demographic patterns and quantify visual changes in morphology in small, newly found R. geographicum thalli. This thesis marked the first attempt at creating an age-specific cohort life table (up to 4 years) and tracking age-specific changes in morphology and survival in R. geographicum thalli.