Epiphytic bryophyte diversity and range distributions along an elevational gradient in Marojejy, Madagascar

Describing spatial variation in species richness and understanding its
links to ecological mechanisms are complementary approaches for
explaining geographical patterns of richness. The study of
elevational gradients holds enormous potential for understanding the
factors underlying global diversity. This paper investigates the
pattern of species richness and range-size distribution of
epiphytic bryophytes along an elevational gradient in Marojejy National
Park, North-east Madagascar. The main objectives are to describe
bryophyte species composition and endemism in Marojejy National
Park, to describe the species richness and distribution patterns
of epiphytic bryophytes along an elevational gradient from 250 m
to 2050 m and to evaluate the explanatory value of environmental
variables for the observed patterns. Bryophyte samples
were collected following a nested design with four hierarchical
levels: elevational belts, plots, quadrats and microplots. In
total, 254 epiphytic bryophyte species were recorded, comprising
157 liverworts and 97 mosses. Twenty-three of these are endemic
to Madagascar. Species richness exhibits a hump-shaped pattern
along the elevational gradient, peaking at 1250 m. Eighty seven percent of
the total recorded species have a range distribution lower than 1000 m, at
which point 36% are restricted to these single elevations. Our
results suggest that mean temperature, relative humidity and
vapour pressure deficit play important roles in shaping the richness
pattern observed in this study. While the liverwort richness
pattern did not correlate to vapour pressure deficit and
responded only weakly to relative humidity, the richness pattern shown by
mosses correlates well with mean temperature, relative humidity
and vapour pressure deficit.