Spider (Arachnida

Abstract

Green roofs are emerging as potential habitats for biodiversity within urban environment. However, studies on biodiversity on green roofs, its ecological functions and the difference to those of other urban habitats at ground-level are limited to certain geographic range. Spiders (Arachnida

araneae) are frequently studied taxa in understanding urban habitats for their importance in providing ecological functions and representing higher trophic structure. In this regard, this study assesses the spider communities on urban green roofs and ground-level habitats and examines what environmental factors influences spider community composition. Spider communities were compared at species and predatory guild level, in order to assess whether spider communities of two different habitat types provide different ecological functions. Spider community was surveyed using pitfall traps on 12 intensive green roofs of gu (district) office buildings and 12 adjacent ground-level habitats in Seoul, South Korea. Age, area, height, plant structure and surrounding landuses within 300m radius were surveyed as environmental variables. Spider communities were grouped into two groups by hierarchical cluster analysis. Non-metric multi-dimensional scaling was used to visualize compositional difference of spider communities and environmental variables explaining the composition. Analysis of similarities and similarity percentages analysis was performed to examine the significance of difference in spider community compositions. The results revealed that araneae community of each habitat type was significantly different, although some communities of green roof sites and ground-level sites were similar in composition. The compositional difference was explained by shrub and soil cover, and height of habitats, while landscape variables did not explain the compositional difference of spider communities. Difference in guild structure by habitat types suggest the functions of spider communities in each habitat could be different. Thus, perception of green roofs should not just be a surplus of green areas in urban environment, but a provision of distinct ecological communities, which is critical in terms of ecosystem services and biodiversity conservation.