The Effects of Resource Enrichment on the Diversity of Plants and Arthropods in a Shortgrass Prairie

A shortgrass prairie in northeastern Colorado was subjected to nutrient enrichment by irrigation, nitrogen fertilization, and irrigation plus fertilization over a 3-yr period. Irrigation plus fertilization had the greatest effect on both the plant and arthropod communities. Primary production increased and plant species diversity declined while both arthropod diversity and biomass increased in response to this treatment. Irrigation or fertilization alone had less of an effect, with diversity and biomass increasing on these 2 treatments in both the producer and consumer communities. The arthropods showed only limited response to plant quality measured by the concentration of N in plant tissues and by the abundances of warm and cool season plants. Although plant species' information content (H'pp) was significantly correlated with arthropod diversity, unknown treatment effects had the greatest influence on arthropod diversity. Also, a negative correlation between arthropod size and abundance resulted in H'poP and equitability, when measured with biomass, to be significantly greater than when measured with numbers.