Effects Of Habitat Fragmentation On Avian Nest Predation Risk In Thousand Island Lake, Zhejiang Province

Habitat fragmentation is a major factor that affects population survival and leads to biodiversity loss. Habitat fragmentation can affect the habitat environment and spatial characteristics. It also can impact predator species and abundance, thus influencing avian reproductive success, especially for those birds with distributions at the edge of a habitat.Thousand Island Lake was created in1959by the damming of the Xinanjiang River in western Zhejiang Province for the purpose of generating hydroelectricity. These land-bridge islands are ideal natural labs for studying habitat fragmentation and edge effects because of their simultaneous isolation, clear boundaries and homogeneous matrix.To investigate the effects of habitat fragmentation on avian nest predation risk, we placed726artificial ground nests with chicken(Gallus gallus domesticus) or quail (Coturnix japonica) eggs at16islands in edge and interior locations in Thousand Island Lake from April to August2010. We compared the nest predation rates between the nests with different egg types and between the nests located at different sites. We also evaluated the relationships between nest predation and island area, isolation, shape index and plant richness. The results were as follows:(1) We used a2-way factorial ANOVA to test the ability of egg type (chicken vs. quail) and location (edge vs. interior) to predict the predation fate of nests. The results showed that: predation rate was higher for nests containing quail eggs (81.2%) compared to chicken eggs (60.0%), and lower at the interior than at the edge (66.1%vs.75.1%). The results suggested that habitat fragmentation could increase avian predation risk as a result of edge effects, and that birds with small eggs might be more sensitive to fragmentation.(2) We used a log transformed linear model to analyze the relationships between the predation rate of nests and island area, island isolation, island shape index and plant richness. The results showed that:isolation and plant richness had no relationship with nest predation rate (P>0.05), but island area and island shape index were positively related with nest predation rate (P<0.05). These results suggest that habitat fragmentation could also increase avian predation risk as a result of area effects.(3) On small islands, we used a one-way factorial ANOVA to test the ability of location (edge vs. interior) to predict the predation fate of nests containing different egg types. The result showed that no matter what egg type the nest contained, predation rate showed no difference between nests located at the edge versus the interior region (P>0.05). This may suggest that the entire area of small islands is effectively edge habitat, and thus there are no differences between nests located in different regions on small islands.(4) We used a one-way factorial ANOVA to test the ability of breeding time (April vs. June vs. August) to predict the predation fate of nests containing different egg types and located at the edge or interior region. The results showed that predation rate is higher in August than in April or June.