Contrasting effects of habitat fragmentation on community stability of breeding and wintering birds in urban green spaces

Green spaces are crucial refuges for biodiversity conservation in urban environments with the accelerating rate of urbanization worldwide, which threatens their effectiveness in maintaining stable wildlife communities. While many studies have examined the effects of habitat fragmentation on community stability in natural landscapes, it is still unknown how habitat fragmentation and species traits shape wildlife community stability in urban green spaces. Here, we surveyed bird communities over five years in 19 green spaces along an urbanization gradient in Shanghai, China. In our study, habitat fragmentation was characterized by high edge density and high patch isolation of a particular urban green space in a highly urbanized area. We measured community stability as the temporal invariability of the total community abundance and partitioned it into population asynchrony and population stability. We thus explored how habitat fragmentation and species traits (measured as functional diversity) affect the community stability of urban birds. We found that bird functional diversity reduced community stability through population stability in the breeding and winter seasons. Habitat fragmentation increased community stability indirectly through functional diversity in both seasons. Furthermore, habitat fragmentation decreased the stability of bird communities through population asynchrony only in the breeding season. Our findings demonstrate the negative relationships between functional diversity and community stability in urban areas. Moreover, the contrasting seasonal effects of habitat fragmentation suggest that urban green space planning strategies should be seasonally adaptive. Connecting fragmented habitats is essential in the breeding season to support functional diversity and stability, while maintaining a certain level of fragmentation in winter may help stabilize communities.