Effects of artificial night lighting on a web-building spider species in urban green spaces

Urban green spaces are biological habitats that play an important role in maintaining urban biodiversity and are affected by artificial light at night (ALAN). Determining the effects of ALAN on predators in urban green spaces is important for promoting the maintenance and conservation of these functions of insect communities in urban green spaces. We investigated the effects of ALAN on a web-building spider species (Trichonephila clavata) in urban green spaces in the Tokyo metropolitan area, Japan. We used a GPS receiver to determine the positions of streetlights and spider webs and classified the webs into two groups: those within the reach of streetlights and those outside their range. We then measured the web distribution (web density), web size, female traits (femur length and body weight), and male presence. Web densities in the light conditions were higher and web sizes smaller than those of webs in the no light conditions. Female body weight and length were also significantly lower in the light conditions than in the no light conditions. However, female body condition and male abundance did not differ between the light and no light conditions. Our results showed that T. clavata maintains some degree of fitness in urban fragmented green spaces although their physical characteristics and behaviour are altered by ALAN. Therefore, we suggest that measures to improve the quality within green infrastructure are required to maintain the function of generalist predators such as web-building spiders in urban green spaces.