Local and landscape-scale environmental filters drive the functional diversity and taxonomic composition of spiders across urban greenspaces.
Abstract
Urban patch colonization and species establishment within cities are restricted by the behavioural, life history and physiological attributes of colonizing species, in conjunction with environmental filtering processes at small and large spatial scales. To enhance the local biodiversity in urban greenspaces, these filtering processes need to be assessed so that greenspace design and management can guide establishment of local species pools. We investigated the relative importance of local and landscape-scale features on spider community assembly using a functional and taxonomic approach. Within the city of Cleveland, Ohio, USA, we established a field experiment wherein control vacant lots, urban meadows, and low- and high-diversity pocket prairies were established across eight neighbourhoods (N = 32). Spiders were sampled during June-August of 2015 and 2016 using pitfall traps and vacuums. Spider functional diversity was assessed using null models, while local and landscape drivers were analyzed via canonical partial least squares and clustered image maps. Increased mowing was associated with lower-than-expected spider functional alpha and beta diversity in 2015. Patch isolation and percentage impervious surface increased the functional dissimilarity and taxonomic diversity of spiders in 2016, resulting in higher-than-expected overall functional alpha diversity. We also found that increasing plant height and biomass favoured spiders with large body size and decreased the abundance of small web weavers. Synthesis and applications: Our findings suggest that increasing the amount of impervious surface in cities will act as a strong environmental filter, producing more spatially distinct spider communities at a landscape scale. Additionally, while periodic mowing in vacant lots benefits some spider taxa, it has a negative impact on the establishment of several species, mainly larger spiders and those most sensitive to disturbance. To conserve spiders and the biota depended upon them, investment in managed greenspaces such as pocket prairies that require infrequent mowing is warranted. In doing so, cities can enhance urban biodiversity and beautify local neighbourhoods.