The structure of the flower–insect visitor system in tall-grass prairie

Tall-grass prairie is endangered by habitat loss and fragmentation, and climate change. Flower-visiting-insect activity on two tall-grass prairie communities, one larger and more mesic than the other, was examined to determine network structure, and temporal and spatial variation. Flower-visiting insect richness and visitation rate were monitored for 2 years. Most insect-visitor taxa were Diptera, followed closely by Hymenoptera. Only 18% of insect taxa visited both communities in both years, but were responsible for 70% of all visits. The three most active insect species were Toxomerus marginatus Say, Bombus ternarius Say, and Odontomyia pubescens Day. The core plants, receiving over 67% of all visits, were Solidago canadensis L., Solidago rigida L., and Zizia aptera (Gray) Fern. Seasonal differences in insect visits were primarily due to temperature, as well as normal phenological patterns. Diptera was more abundant at one site, likely owing to differences in the quantity of nearby aquatic larval habitat. The mutualistic network of these two tall-grass prairies is significantly nested, which may make it more resilient to environmental perturbations than systems that are more compartmentalized.