While it is recognized that many communities undergo large seasonal changes, the consequences for spatial structure of communities are poorly known. Previously studies found that individual bird species may alter their habitat use and foraging behaviors in response to seasonal changes in habitat structure and the availability and distribution of resources. Consequently, bird communities may vary in structure and beta diversity across seasons. However, most studies of bird community structure may have overlooked seasonal differences. We used an island habitat system (Thousand Island Lake, China) to evaluate seasonal variation in forest bird communities by grouping landbird communities into winter residents, winter visitors and summer residents. We then used beta diversity partitioning, nestedness (NODF) and stochastic null communities to test for differences among these bird. We asked the following questions: (1) Do winter residents have different overall beta diversity and its turnover vs. richness components compared to winter visitors and summer residents? (2) Are such differences related to island area, geographic distance, or habitat diversity? (3) Does nestedness vary between seasons or with migratory status, and are there any differences related to island area or distance? (4) Are differences in beta diversity components significantly different from randomly assembled communities?
Results/Conclusions
Beta diversity of winter residents was high and mainly driven by richness differences, whereas that of summer residents was low and dominated by species turnover. Winter visitors showed similar nestedness to randomly-drawn assemblages, and were less frequently different from random null communities than winter and summer resident communities. Island area differences between islands were related to beta diversity patterns, and such effects were strongest and most predictive for winter residents, followed by summer residents, and weakest and least predictive for winter visitors. Mantel correlations between habitat richness and the turnover or richness components of beta diversity were also weaker for winter visitors than for summer or winter residents, and the partial correlation values for habitat richness were only significant for summer and winter residents, and not winter visitors. The results suggest a selective extinction process for winter residents, probably related to winter food shortage. Conversely summer residents appeared more dependent on turnover in local factors, such as habitat conditions, which mediate competition. Winter visitors appeared randomly distributed across islands. Our analyses indicate strong seasonal differences and differences between resident species and seasonal visitors in their spatial community structure as revealed through turnover and nestedness.