The mechanisms of maintenance of plant diversity and community assembly rules in the Thousand Island Lake region, East China

Background/Question/Methods Habitat loss and fragmentation is the primary threat to biodiversity. However, it is difficult to study the effects of habitat loss and fragmentation experimentally because of a number of methodological and logistical reasons. Land-bridge islands formed by dam construction are ideal natural labs for studying habitat loss and fragmentation because they were formed around the same time and have well-delineated boundaries and a homogeneous matrix (water) – features that terrestrial habitat and oceanic islands do not always possess. The Thousand Island Lake region in southeastern China has more than 1000 islands formed by damming a river in 1959. Since 2007, we have investigated species richness, functional traits, and structure of plant communities on more than 150 of these islands with different size, shape, and degree of isolation. Our objectives were to assess the effects of habitat fragmentation on species diversity and community organization and to understand the underlying mechanisms of biodiversity dynamics and community assembly.

Results/Conclusions Our field surveys recorded 541 plant vascular species on 156 islands of sizes ranging from 0.02 and 1153.88 ha. The species-area relationship (SAR) for the 156 studied land-bridge islands is: S = cA^z, z = 0.17, R² = 0.56. Our analysis showed that isolation contributed much less to the variation in species diversity (R²=0.03). Based on the geographic isolation by rivers before dam construction, we divided all sampled islands into three groups and computed SARs for each. Z-values of SARs of these groups showed different sensitivities of species diversity to habitat loss. We also found that a group of islands had more species than a single island with the same total area. This difference, however, declined as the total area or the number of islands in the group increased. Overall, our study indicates that habitat loss plays a more important role in maintaining plant biodiversity than habitat fragmentation in the Thousand Island Lake region, and the factors at different scales affect the community organization and assembly rules.