Bird Community Structure And Functional Diversity Pattern On Subtropical Land-bridge Islands

Habitat fragmentation is one of the greatest threats to global biodiversity as reduced habitat area and increased isolation almost invariably lead to rapid declines in local species richness and/or to increased extinction risks of remnant populations. We used guild abundance and functional diversity to explore the changes in bird community structure, understand species variations across different vegetation types and patterns of functional diversity on fragmented system.We censused the presence and abundance of bird species on each of the41study islands using standard line transect methods. Birds were censused during the breeding seasons (April-June) and winter seasons (November-January) each year from2006to2009. Applying the guild approach in such systems, the results were as follows.1) Bird communities at TIL were dominated by insectivores, omnivores or understory and canopy guilds.2) Our data showed that migrants and residents responded equally to island area, insectivores and understory guilds were sensitive to island area but omnivores and canopy guilds were not very sensitive.3) Most bird guild abundance was determined by island area, except for omnivores and canopy guilds. Although perimeter-area ratio (PAR) or habitat diversity found to be important for bird species richness, our results highlight the importance of island area in maintaining bird diversity in fragmented island systems.When applying a measure of functional diversity, the results were as follows.1) There were no correlations between FRic and FEve, FEve and FDiv, but negative correlations between FRic and FDiv.2) As predicted, island area accounted for most of the variation in bird species richness, whereas isolation explained most of the variation in species diversity and had negative impacts on species evenness.3) FRic increased with island area but FEve decreased with island area, and FDiv showed no clear patterns.4) Functional diversity appears to be more strongly influenced by habitat filtering as opposed to limiting similarity. Specifically, both FRic and FEve were significantly less than expected across all islands, but FDiv showed no clear patterns.5) Our findings support the need for the effects of fragmentation on functional diversity to be explicitly considered in reserve design. For example, low FEve values on large islands and/or patches may indicate low functional stability and as such these islands and/or patches may deserve extra attention and/or protection.Our analyses showed that the classic species-area model gave a better fit than the proposed model (species-area-habitat model).