Species-area relationship and small-island effect of bryophytes on the Zhoushan Archipelago, China

Aim The species-area relationship (SAR) and the small-island effect (SIE) are of important ecological significance. However, few studies have focused on these topics in regard to bryophytes. We aimed to (1) determine whether SIEs and a SAR with two thresholds and three different processes of species addition exist for bryophytes across continental islands and (2) test whether the SIE threshold tends to be high for stenoecious species with a high sensitivity to habitats and for those with relatively high resource requirements and low dispersal abilities. Location The Zhoushan Archipelago, China. Taxon Bryophytes. Methods We obtained species number data for five bryophyte categories (total bryophytes, total mosses, acrocarpous mosses, pleurocarpous mosses and liverworts) from 66 continental islands of the archipelago and analysed the dataset using 24 SAR models. According to Akaike's information criterion, we identified models suitable for revealing SARs and detecting SIEs among the five bryophyte categories. Results The power model was best for fitting SARs of all bryophyte categories except for pleurocarpous mosses. For detecting SIEs, the three-segmented model provided the best support for the five categories. There were obvious SIEs for the five bryophyte groups, with area thresholds of 0.11-1.42 km(2). The SIE threshold was much higher in liverworts than in mosses and in pleurocarpous mosses than in acrocarpous mosses. The second thresholds for the five categories were similar, ranging from 53.62 to 73.19 km(2). Main conclusions A unique SAR pattern with two area thresholds and three different dominant processes of species addition with island area was found for bryophytes across the continental islands. The second thresholds were not due to in situ speciation but were likely due to the high immigration of bryophytes from the mainland attributed to local residents. The SIE thresholds detected for the different categories of bryophytes indicated that the values tended to be low for species groups with low resource requirements and high dispersal abilities and high for those with a high sensitivity to habitat conditions, the latter indicating that areas for conservation purposes for species sensitive to habitats should be comparatively large.