Aim: To assess habitat filtering and dispersal limitation in spore plant community assembly using bryophytes on recently emerged land uplift islands as study system.

Location: Gulf of Bothnia, northern Europe.

Taxa: Bryophytes, including the spore plant phyla Bryophyta (mosses) and Marchantiophyta (liverworts).

Methods: The species compositions of 20 coastal land uplift islands differing in age, area, connectivity, and habitat composition were recorded in the field. In addition, we compiled a list of the regional species pool (446 species) and gathered data on species traits related to habitat affiliations (substrate, light, moisture, and pH) and dispersal capacity (regional abundance, spore size, sporophyte frequency, sexual system, vegetative propagules). For the 420 species with available trait data, we used multivariate generalized linear models to compare trait effects on species occurrence probabilities on the islands.

Results: Occurrence probabilities depended strongly on habitat affiliations. In addition, occurrence probabilities were lower for predominantly asexual species than for sexual species and for regionally rare than for regionally abundant species. Having specialized asexual propagules increased occurrence probabilities, but compensated only partly for the reductions in asexual species. No effect of the size of sexually produced spores was detected. Comparison of trait effects across island size and connectivity gradients revealed (i) reduced habitat filtering on larger islands and (ii) decreasing negative effects of being predominantly asexual with increasing island connectivity.

Conclusions: Both habitat filtering and dispersal capacities affect the community assembly of spore plants on land uplift islands. Asexual mosses and liverworts show landscape scale (≤ 10 km) dispersal limitation. The weak or absent relationships between island connectivity and the effects of dispersal traits suggest that colonization is regulated mainly by habitat availability and the abundance of each species in a “regional spore rain” from which colonists are recruited.

Data and R code for the paper Bryophyte community assembly on young land uplift islands - dispersal and habitat filtering assessed using species traits. In Journal of Biogeography.