Species richness and metacommunity dynamics in bryophytes

Abstract

Bryophyte species richness and composition were analysed on limestone boulder habitats across twenty sites in Malta. These boulders acted as standard units for studying the effect of environmental, microtopographical and spatial factors on bryophyte metacommunities. The results indicated that bryophyte species richness on boulders was not significantly affected by environmental and spatial parameters. In fact the variability of within-site species composition was comparable to across-site variability, and spatial separation had a negligible effect on differences in species richness (p=0.04, R2=0.05) between sites. This result along with the fact that 78.1% of the thirty-two bryophyte species sampled showed no significant preference between boulders and the surrounding soil matrix suggest that the composition of local bryophyte communities was not limited by dispersal between boulders. Instead, environmental and spatial parameters were more likely to influence the occurrence of particular bryophyte species on limestone boulders. The same could not be said for microtopographical parameters, which were found to significantly contribute to variation in bryophyte species richness and composition. This result confirms previous remarks about aspect and slope being the most ecologically meaningful predictors of bryophyte species composition on boulders (Vitt, Li & Belland 1995; Spitale & Nascimbene, 2012). Such parameters were more important than general environmental conditions within a site, because they control micro-fluctuations in light and moisture conditions and consequently govern the physiological adaptations of bryophyte communities. Species richness also showed a positive and significant relationship (p<0.01, exp(B)=1.39) with standardised boulder surface area, confirming the area predictions of island biogeography theory. From the four metacommunity perspectives (Leibold et al., 2004), only the neutral paradigm was not observed. This suggested that an amalgamation of metacommunity paradigms govern bryophyte species composition on local limestone boulders, with the order of colonisation, extinction and interspecific competition having a significant role in shaping such communities.