Cultivated milkweed hosts high diversity of surface-active and soil-dwelling arthropods in a New England case study

Abstract

New land uses can drive complex changes to local biodiversity. In the Northeastern U.S., cultivated milkweed has arisen as a new crop with potentially promising outcomes for monarch butterflies, but has unknown effects on surface-active and soil-dwelling arthropods. We assessed differences in arthropod communities among nearby sites containing milkweed and three common regional land uses: conventional corn, conventional hay, and forest, representing a spectrum of high to low land use intensity. In each land use, we sampled surface-active and soil-dwelling arthropods, and we classified organisms at the taxonomic order level for all collected arthropods and at the taxonomic genus level for surface-active beetles. To address differences in functional traits between sites, we measured organisms’ body sizes and calculated average body mass, total biomass, and abundance of arthropods in small, medium, and large size classes. In almost all analyses, taxonomic diversity values were significantly higher in the milkweed site than in corn and similar between the milkweed and hay sites. Milkweed had significantly higher diversity of surface-active arthropods than forest (for both orders and beetle genera), but did not have higher diversity of soil-dwelling arthropods, indicating possible different mechanisms driving aboveground versus belowground trends. Community composition differed significantly among land uses (demonstrated in NMDS ordination plots), with milkweed most similar to hay. Body size analyses demonstrated high total biomass and generally higher abundance of larger individuals in milkweed than in other land uses, with the exception of corn, which was dominated by large carabid beetles. We discuss the implications of our findings to land use properties and ecological function. Our case study indicates promising benefits of milkweed cultivation for soil biodiversity and soil health, with more research needed to validate and build from our results.