Plants regulate grassland arthropod communities through biomass, quality, and habitat heterogeneity

Habitat heterogeneity affects both biotic and abiotic factors important in determining arthropod community composition. In a sandy, mixed‐grass prairie in the southern Great Plains, we used clipping and NPK fertilization to manipulate plant biomass, habitat heterogeneity, and plant quality to quantify their relative effects on the abundance and diversity of its arthropod community. Both clipping and fertilization treatments affected plant biomass and microclimate, including light availability, temperature, and humidity. By decreasing plant biomass, clipping simplified habitat structure and resulted in reduced arthropod abundance and diversity and increased arthropod activity. This reduction appeared to be mediated by fertilizer addition, which increased total plot carbon, plant biomass, and habitat volume, resulting in lower average surface temperature and higher average humidity. By itself, increasing plant biomass through fertilization increased arthropod abundance, activity, and richness. In addition, we show that changing microclimate and plant biomass promoted shifts in arthropod community composition. These results demonstrate the role of habitat heterogeneity and plant quality in structuring arthropod community composition, specifically by regulating microclimate and providing habitat space. Plant biomass, plant quality, and habitat heterogeneity are three key factors shaping abundance, diversity, and species composition of grassland arthropods (Dennis et al. 1998, Lassau and Hochuli 2004, Arnan et al. 2007). For animals the size of arthropods, variation in plant biomass (sparse or dense), and vegetation spacing (clumped or uniform) combine to generate habitat heterogeneity (Landis et al. 2000, Langellotto and Denno 2004). This heterogeneity in turn can shape arthropod abundance and diversity via its effects on microclimate (Wan et al. 2002), food availability and variety (Báldi 2008), and arthropod competitive interactions (Langellotto and Denno 2004, Janssen et al. 2007). Given the important role that plant diversity plays on insect diversity (Haddad et al. 2001) and that short‐term fertilization changes plant biomass but not diversity (Haddad et al. 2000), one effective way of manipulating both plant quality and quantity but not plant diversity are short‐term, or pulse, fertilization experiments. We explore how a one‐year pulse experiment generated a cascading effect on a grassland arthropod community. Fertilization can shape grassland arthropod abundance in at least two ways: via increasing plant biomass (Tilman 1986, LeBauer and Treseder