Niches and guilds of bryophytes along a 3000-meter elevational gradient

Abstract

A long and steep elevational gradient presents the opportunity to study the niches of a large number of species within a small geographic area. Along such a gradient in the Sierra Nevada of California, all bryophytes were recorded in 253 plots. Along with species occurrence, the wetness, incline, shadiness and substrate type of the spot where each bryophyte was living were recorded. The average of these ecological traits (i.e., the central tendency of the species niche) was tabulated along with a determination of whether the species was a specialist or generalist for that niche dimension. Moving to guilds, co-occurrence in plots was used to aggregate species into ecological coalitions using the program RCLUS. These coalitions occupy different parts of an ordination of species, but they reveal more subtlety than the ordination itself. An ecotone was evident between the foothill bryophyte vegetation zone and a higher elevation zone. Other ecotones were not obvious; for example, we did not detect a sharp boundary between a conifer zone and a subalpine zone, rather the turnover of species was incremental and individualistic. For naturalists who know the species, being able to characterize them ecologically contributes to thoughts of the assembly of communities and the conservatism of clades.