Relating rarity and phylogeny to the autecology of mosses: A comparative study of three rare-common species pairs in the Front Ranges of Alberta, Canada

Rare species may have ecological characteristics in common that either as a result of or in response to their restricted distributions. These similarities are most soundly documented through autecological comparisons based on closely related rare-common species pairs that control for phylogeny. In this thesis, three rare species, Mielichhoferia macrocarpa, Didymodon johansenii, Mnium arizonicum, and three common species, Bryum pseudotriquetrum, D. rigidulus, M. spinulosum, respectively matched, were compared by assessments of habitat specificity, establishment ability, stress tolerance, propagule viability, colony demography, influence of disturbance regime and frequency of neighbor contact. In general, ecological differences between rare and common species were found, and in an analysis of ecological traits pertaining to local persistence the rare species clustered together. Two of the rare species most similar to each other, M. macrocarpa and D. johansenii, were restricted during the establishment stage, and these two species have similar widely disjunct distributions. In contrast, M. arizonicum is endemic to North America and ecologically very similar to its common congener. Mnium arizonicum was concluded to have the physiological ability to expand its range in the establishment and adult stages, and may be dispersal limited. Two common species had clear physiological limitations mainly in the adult stage, and the third, D. rigidulus, was limited during the establishment stage. As with M. macrocarpa and D. johansenii, this establishment restriction corresponded to substrate specificity confirming the link between these two factors in mosses. Physiological substrate restrictions were documented for M. macrocarpa and D. rigidulus, species found on substrates with high pH and low organic matter, while D. johansenii was physically limited by disturbance. The effect of habitat disturbance regimes varied between establishing propagules and established colonies. Species with lower colony disturbance tended to have more frequent neighbor encounters as predicted by plant strategy theory. Propagule viability did not relate to establishment ability suggesting that dispersal and establishment are functionally separate in mosses and should be treated separately in metapopulation models. The complexity of mechanisms responsible for habitat specificity and narrow realized niches shown here agrees with predictions of several rarity hypotheses and, more importantly, demonstrates the necessity of empirical studies to test these hypotheses.