Meta-analysis of urbanization effects on spider diversity reveals guild-specific negative and positive impacts

Urbanization has been shown to have broadly negative impacts on arthropod diversity and abundance. However, investigations of urbanization effects on spiders specifically have been relatively few and shown minimal clear patterns. We conducted a meta-analysis on the urbanization impacts of spiders globally, examining moderators including guild type, urbanization intensity, climate classification, biome, and dispersal ability. From 28 studies of 27 sites, we extracted data for 99 observations of abundance and 101 observations of richness of spider urban/natural comparisons. Overall, we found no significant effects of urbanization on spider abundance or richness. We also detected no modulation of dispersal ability, biome, or urbanization intensity on the urbanization effect of spider species richness and abundance. However, guild type emerged as a key moderator of urbanization impacts, as orb-weaver spiders had increased abundance and richness in urban sites while sheet web weavers had reduced richness. Our results highlight that not all arthropod groups respond to urbanization similarly – within spiders, variation in responses highlights the need to consider differential impacts of urbanization on spider guilds. Given the diversity of spiders globally and their crucial roles in ecosystems, our results demonstrate that urban conservation strategies must account for guild-specific habitat requirements rather than treating spider assemblages as uniform units. Incorporating such trait-based considerations into urban planning represents a priority for maintaining predator diversity in urban landscapes.