Responses of predatory invertebrates to seeding density and plantspecies richness in experimental tallgrass prairie restorations

In recent decades, agricultural producers and non-governmental organizations have restored thousandsof hectares of former cropland in the central United States with native grasses and forbs. However,the ability of these grassland restorations to attract predatory invertebrates has not been well docu-mented, even though predators provide an important ecosystem service to agricultural producers bynaturally regulating herbivores. This study assessed the effects of plant richness and seeding density onthe richness and abundance of surface-dwelling (ants, ground beetles, and spiders) and aboveground(ladybird beetles) predatory invertebrates. In the spring of 2006, twenty-four 55 m × 55 m-plots wereplanted to six replicates in each of four treatments: high richness (97 species typically planted by TheNature Conservancy), at low and high seeding densities, and low richness (15 species representing a typ-ical Natural Resources Conservation Service Conservation Reserve Program mix, CP25), at low and highseeding densities. Ants, ground beetles, and spiders were sampled using pitfall traps and ladybird beetleswere sampled using sweep netting in 2007–2009. The abundance of ants, ground beetles, and spidersshowed no response to seed mix richness or seeding density but there was a significant positive effect ofrichness on ladybird beetle abundance. Seeding density had a significant positive effect on ground beetleand spider species richness and Shannon–Weaver diversity. These results may be related to differencesin the plant species composition and relative amount of grass basal cover among the treatments ratherthan richness