Tropical bryophyte floras: a homogeneous assemblage of highly mobile species? Insights from their spatial patterns of beta diversity.

The impact of Pleistocene climate changes substantially varied between tropical regions, resulting in striking differences in angiosperm species richness caused by post-glacial recolonization delays. Tropical bryophytes, which have been perceived as extremely good dispersers due to biased rates of monoecy and hence spore production, differ strikingly from angiosperms in their similar patterns of species richness among tropical regions. Here, we analyse the patterns of beta diversity of tropical bryophytes to determine whether their high dispersal capacities have balanced patterns of species richness and erased any difference of post-glacial recolonization patterns between tropical regions. The partitioning of beta diversity for 7485 tropical moss species among 164 operational geographical units (OGUs) and 3276 liverwort and hornwort species in 154 OGUs revealed a slight, but significantly higher beta diversity among than within tropical regions. The nestedness component of beta diversity did not significantly differ between tropical regions. This indicates that, although regional migration rates were sufficient to erase differences of the impact of Pleistocene climate changes between tropical regions, the similar bryophyte species richness of tropical regions cannot be interpreted in terms of unrestricted migrations and that oceans act as a barrier to routine dispersal, which is sufficient to shape largescale floristic patterns. [ABSTRACT FROM AUTHOR]