Mating system, reproduction mode and diaspore size affect metacommunity diversity

Abstract

1 Metapopulation persistence and metacommunity diversity in patchy dynamic landscapes critically depend on efficient dispersal. Dispersal strategies could involve trade-offs that result in different species responses to habitat fragmentation, alteration in habitat quality and changes in landscape dynamics. 2 We studied spatial structuring in species richness of obligate epiphytic bryophytes in 135 deciduous forest patches in a largely coniferous landscape in Sweden. We tested the effects of forest patch size (0.01–15 ha), patch quality and present and historic connectivity (as revealed by air photographs) on species richness of species groups with different mating systems, reproduction modes and diaspore sizes. 3 Present connectivity to other deciduous forest patches had positive effects on richness of dioecious species with predominant asexual reproduction, whereas richness of monoecious species with predominant sexual reproduction was affected by historic connectivity only. The scale of spatial structuring in species richness increased with decreasing diaspore sizes. Forest patch quality affected richness of monoecious species reproducing sexually but not of dioecious species reproducing asexually. 4 Our results suggest shorter dispersal distances, but higher establishment rates, of large asexual diaspores than of small sexual ones. In monoecious species with sexual reproduction, it may take several decades from establishment to first spore production, and this may explain the strong effect of historic, but not present, forest patch connectivity on species richness of this group. This suggests a trade-off between dispersal distance and age at first reproduction, which may explain the parallel evolution of asexual reproduction and monoecism in species inhabiting patchy, transient habitats. 5 Synthesis. We conclude that dispersal success of metacommunity members is influenced both by species traits and habitat characteristics. In patch-tracking metacommunities, trade-offs in species traits may have evolved as a consequence of conflicting selection pressures imposed by habitat patchiness and dynamics. Syndromes of interrelated species traits imply that fairly small changes in habitat conditions may lead to distinct changes in metacommunity diversity: Species reproducing asexually may drastically decline with increasing distances among patches, whereas sexually reproducing species may decline with increasing patch dynamics.