To what extent does vegetation composition and structure influence beetle communities and species richness in private gardens in New Zealand?

Abstract

Private gardens comprise a large proportion of urban green space and can contain diverse and structurally complex vegetation, typically dominated by exotic species, but potentially providing resources for a diverse invertebrate fauna. We determined how much beetle diversity and community structure were influenced by vegetation composition and structure, native vegetation, garden land covers, and proximity and extent of neighbourhood green spaces in 55 gardens in Dunedin, New Zealand. We recorded 164 species from 29 families after 10 days of pitfall trapping; 68% native, 15% exotic. Beetle diversity exceeded that reported in other less modified New Zealand habitats, possibly due to high habitat heterogeneity at the scale of the garden but also the variety of habitats present at a larger scale but separated by relatively short distances within this small city and across a short altitudinal gradient, from sea level to sub-alpine environments. Number of shrubs (2–5m), woody plant density, and area of lawn and hedge influenced beetle richness, diversity and community structure, but explained <30% of variation between gardens. We found no effect of mean diversity of herbaceous vegetation in bed use, mowing and composting on diversity or community structure. Proximity to green space, woody plant diversity and vegetation structural complexity influenced beetle community composition, but correlations were weak. Although only 17% of all woody plants were native, most beetle species were native. With the exception of gardens that had very little vegetation, landscaping choices appeared to have little effect on beetle diversity and assemblage composition.