Patterns of Microhabitat Occupation of Six Closely Related Species of Mosses Along a Complex Altitudinal Gradient

Abstract

Patterns of microhabitat occupation were studied for six species of closely related mosses along a complex altitudinal gradient spanning 1600 m on the northeast face of Mount Washington, New Hampshire, USA. Differential patterns of distribution were noted among species along the axes of percent incident light, substrate type, soil texture and soil pH. The ecotope breadths of Polytrichastrum species were approximately double the ecotope breadths of Polytrichum species. Factors capable of producing ecotope separation among Polytrichum species were insufficient for achieving ecotope separation among Polytrichastrum species. The observed patterns suggest that the two genera have evolved in different ways to achieve separation among species. Evidence for competition regulating the relative distribution of these six species was weak. In general, overlap increased with increased in co—occurrence of particular species pairs. Ecotope breadths were unaffected by the presence of closely related species. Species were packed more closely along dimensioned axes than is predicted by competition theory. The problems of interpreting overlap indices as indices of competition intensity are discussed.