Dispersal and coexistence of mosses (Splachnaceae) in patchy habitats

(1) Three mechanisms that may promote the coexistence of the boreal mosses Tetraplodon angustatus. T. mnioides, S. ampullaceum and S. luteum (Splachnaceae) have been examined: differences between dry and wet habitats; seasonal segregation of resources, and interspecific dispersal differences. These mosses grow on the droppings of large mammals and have their spores dispersed by flies (Diptera). (2) Droppings located in dry habitats were primarily occupied by Tetraplodon spp., whereas droppings in wet habitats were primarily occupied by Splachnum spp. In dry habitats there was a seasonal segregation of dropping colonization by Tetraplodon spp. Dung placed into the field in May, when sporophytes of T. angustatus matured, were exclusively colonized by T. angustatus, whereas dung placed into the field in June, when most T. mnioides sporophytes matured, were primarily colonized by T. mnioides. (3) Each species of moss attracted between ten and seventeen species of spore-carrying flies and the fly faunas attracted to each species were 77-92% different from each other in species composition. (4) Neither species of Tetraplodon appeared to have a clear dispersal advantage: for both, spore-carrying flies were predominantly associated with dung in dry habitats; spore-carrying flies captured on T. angustatus carried significantly more spores on average than did spore-carrying flies captured on T. mnioides; however, more flies captured on T. mnioides were found to be carrying spores than were flies captured on T. angustatus. (5) Although more flies captured on Splachnum luteum than on S. ampullaceum, were found to be carrying spores, S. ampullaceum (the weaker competitor) appears to have more of its spores dispersed to dung in wet habitats than does S. luteum. Spore-carrying flies captured on S. ampullaceum and associated dung carried significantly more spores on average than did spore-carrying flies captured on S. luteum, and a much greater proportion of spore-carrying flies associated with S. ampullaceum than with S. luteum were also associated with dung in wet habitats.