Species Turnover And Beta Diversity Of Breeding Bird Communities In Fragmented Habitats

Aim Species turnover broadly contains two facets:temporal and spatial turnovers. Temporal turnover is the pattern of species turnover over time, which is a result of colonization and extinction as proposed by MacArthur and Wilson’s theory of island biogeography (IBT). As expected by IBT, the rate at which species colonize an island depends on the island’s isolation (distance effect), whereas the local extinction rate depends on its area (area effect). Alternative hypotheses recognize that area can affect the colonization rate (target effect) and that isolation can affect the extinction rate (rescue effect) and, moreover, that these relationships may dominate. Spatial turnover describes the extent of species replacement along a spatial gradient, also known as beta diversity. Here, we used long-term counts of breeding bird communities on islands in an inundated lake to quantify the colonization-extinction dynamics of IBT associated with species turnover rates and incidence, and partition beta diversity of bird communities into the components of turnover (due to species replacement) and nestedness (due to species loss or gain) to provide conservation strategies on land-bridge island system.Location Thousand Island Lake (118°34’-119°15’E,29°22’-29°50’N), China.Methods We assessed the occupancy and behaviour of breeding birds on37islands from2007to2012. We estimated the effects of area, isolation and other biogeographical parameters on the fre-quencies of colonization and extinction events using multivariate logistic regression and maximum likelihood estimates. We then extended these results to derived properties such as species turnover rates and incidence. Additionally, we decomposed beta diversity of bird communities into turnover and nestedness-resultant components using the additive partitioning method to explore which com-ponent mainly contributed to regional diversity, and their relationships with differences in island attributes. Results Extinction rates decreased and colonization rates increased on larger islands. Isolation had no significant effect on colonization or extinction rates. Islands had high species turnover overall, and turnover rates followed the same pattern as extinction rates with different areas and isolations. Pool turnover, which controls for the number of species in the pool, was higher on large islands. Species richness also increased with area. Our study of bird communities supported area and target effects, but not distance and rescue effects. We found turnover component contributed more than nestedness-resultant component to beta diversity. Isolation dissimilarity had no effects on these components. The nestedness-resultant component increased with larger differences in island area and habitat richness, respectively, while turnover component decreased with them.Main conclusions Island area was a better predictor of colonization and extinction than isolation, probably because of the relatively small scale (c.580km2) and homogeneous vegetation structure of our research system, and the strong dispersal ability of birds. We conclude that the differences between our observations and theoretical predictions, or results from other studies that measured colonization and extinction directly, are consistent with the particular biogeography of these islands. Our results also indicated that all islands contributed more equally to regional diversity due to the dominance of spatial turnover component that are all potential targets to be protected. We suggested that when considering management policies, both mechanisms underlying nestedness and turnover should be evaluated to prevent misleading actions on biodiversity conservation.