Arthropod and predator abundance and the potential for ecosystem services in California central coast urban gardens

Background/Question/Methods

Urbanization is a major driving force of biodiversity loss in N. America, and may alter the provisioning of ecosystem services. Nonetheless, some urban green spaces, such as community gardens may provide important refuges for biodiversity in the urban jungle. The extent to which community gardens support biodiversity depends on local habitat characteristics of gardens (e.g. crop and herbaceous plant diversity, floral abundance, ground cover, woody vegetation, garden size), and also on surrounding land use (percent of landscape covered in developed land, open space, natural vegetation, and agriculture). For arthropods, a most diverse animal group, local and landscape characteristics influence abundance and species richness, and also impact the degree to which arthropods provide ecosystem services such as pest control. We examined the impact of local and landscape features of 19 urban, community gardens in the central coast of California on arthropod abundance overall, and on the abundance of predators in these garden sites. Between May-September 2013, we surveyed arthropods with pitfall traps, and correlated vegetation and ground cover data surveyed in 1x1, 20x20, and 100x100m plots, and land cover classified at 200m, 500m, 1km, 2km, and 5km scales with arthropod and predator abundance.

Results/Conclusions

We collected a total of 33,088 arthropods, and local habitat features mainly influenced arthropod abundance. Abundance increased with increases in building cover, bare soil cover, and mulch cover at the 100x100m scale, and increased with decreases in grass cover, and increases in leaf litter cover at the 1x1m scale. The only landscape factor that correlated with increases in arthropod abundance was the amount of open space (lawns, parks, golf courses, and urban planted vegetation) within 5km. Major predator groups collected included ants (30% of all individuals captured), spiders (9%), centipedes (2.6%), predatory beetles (2.5%), and harvestmen (1.2%). Again, mostly local factors correlated with abundance of predatory arthropods. Predator abundance increased with increases in lawn cover and numbers of trees, and with decreases in bare soil cover in 100x100m plots, and was higher with more purple flowers and fewer weed species in 1x1m plots. Two landscape factors, agriculture within 500m and open area within 2km correlated with increases in predator abundance. Different predator groups responded differently to individual local and landscape factors. Local habitat factors made up the majority of significant correlates of arthropod and predator abundance, with important implications for management of urban gardens for promotion of ecosystem services.