Spatial patterns and environmental correlates of bryophyte richness: sampling effort matters

Our knowledge of the spatial distribution of bryophyte diversity still suffers from low sampling efforts. Here we try to determine the spatial diversity patterns of liverworts and mosses and their environmental drivers more accurately by correcting for this sampling bias. We compiled bryoflora from 49 localities in eastern China, including data on sampling effort. Both sampling bias uncorrected (raw) species richness and bias corrected (estimated) species richness, as derived from species-sampling curves, were used as response variables. Model selection based on Akaike's information criterion was used to evaluate the impact of collection bias on the selection of environmental and spatial variables in the regression models. Variation partitioning was used to assess the independent and joint effects of environmental, spatial and sampling variables on raw and estimated species richness. Liverwort richness increased significantly with decreasing latitude, while moss richness showed no latitudinal pattern, whether for raw or estimated species richness. However, estimated species richness showed stronger correlation with environmental variables than raw species richness. Importantly, selected environmental variables in the raw species richness models changed after correcting for collection bias. Despite their ability to produce copious amounts of spores, our sampling bias corrected models indicated that bryophyte richness showed strong spatial structuring, indicating dispersal limitation. Environmentally, liverwort richness was primarily controlled by water availability, while the richness of mosses was mainly determined by available energy. Our results highlight that biological features, dispersal ability and environmental sorting may account for the discrepancies between species richness of liverworts and mosses. Given the considerable impact that controlling for sampling effort had on analysis outcome, we like to stress the importance of controlling for sampling bias when studying spatial richness patterns in bryophytes.