Decline in the diversity of willow trunk-dwelling weevils (Coleoptera: Curculionoidea) as a result of urban expansion in Beijing, China

Beijing, the capital and second largest city of China, expanded in a typical concentric pattern. The urbanized area consists of five concentric zones, which are based on the city's ring road system. Willow trees (Salix spp.) are commonly planted and abundant in the city. In this study, we determined the effects of urbanization on willow trunk-dwelling weevils (Coleoptera: Curculionoidea) in a 3-year survey. Our results indicated that species richness and abundance decreased from outskirts to the urban center. It was estimated that within a 30-km limit, species richness and abundance might be reduced by 0.9 species and 59.3% of individuals per 5 km toward urban center. Landscape variables (e.g., the proportion of impervious surface and distance to urban center) explained 59.4% of species richness and 43.9% of species abundance. Local variables (e.g., plant resources and site size) explained only 4.9% of species richness and 4.7% of species abundance. Our results show that there is a negative relationship between urban expansion and weevil diversity. There are several ways in which such detrimental effects on biodiversity could be mitigated: (1) Optimization of urban landscape structures, as well as vegetation planting; (2) increasing connectivity between urban remnants and natural landscapes in the outskirts of the city; and (3) limiting the proportion of impervious surface in inner urban zones.