Monarch butterfly host plant (milkweed Asclepias spp.) abundance varies by habitat type across 98 prairies

Abstract

The decline in migratory monarch butterflies (Danaus plexippus) over the past 20 years has been attributed to several drivers, including loss of their host plants (milkweeds Asclepias spp.). This has sparked widespread interest in milkweed ecology and restoration. We developed a model on environmental and habitat‐type variables to predict milkweed abundance by sampling 93 prairie plantings (47 conservation plantings and 46 roadsides) and 5 unplowed prairie remnants throughout the state of Iowa, United States. Milkweeds were censused in 10–25 random locations within each site, and data on plant diversity, age of planting, soil characteristics, and management were tested as predictors of abundance. Milkweed densities of all species combined were highest in remnant prairies (8,705 stems/ha), intermediate in roadside plantings (1,274 stems/ha), and lowest in conservation plantings (212 stems/ha). Most milkweeds were common milkweeds Asclepias syriaca, which were more abundant in roadside than conservation plantings. Remnants contained the most milkweed species. Total milkweed and common milkweed abundance were both predicted by higher soil pH, a more linear site shape, and lower soil bulk density across restorations. Our results indicate that common milkweed is maintained by disturbance, and establishes readily in rural roadside habitat. Remnants are important as reservoirs for multiple milkweed species and should be protected.

Monarch Habitat in Conservation Grasslands

“…Continued research on a larger sample of sites will further our understanding of the relationship between seeding and management practices and habitat responses across conservation grasslands. Other factors such as landscape context, weather during establishment, and soil characteristics could play a role in the establishment, colonization, and abundance of milkweed and nectar plants (Grman et al, 2015;Kaul and Wilsey, 2019), but these analyses were beyond the scope of our study.…”

Enhancing road verges to aid pollinator conservation: A review

“…Beyond feeding, only five studies (limited to monarch butterflies) have compared the availability and use of resources for other aspects of pollinator lifecycles in road verges to other habitats. They show that road verges have similar or greater densities of milkweeds (larval hostplants) compared to arable fields and restored prairie, but lower densities than remnant prairie (Hartzler and Buhler, 2000;Kaul and Wilsey, 2019) and an average of roughly 25-50% fewer monarch eggs and larvae per milkweed plant than in various non-roadsite habitats (Kasten et al, 2016;Pitman et al, 2018). Future research should compare pollinator nesting, reproduction and overwintering in road verges to in other habitats.…”

Distribution, phenology, and land cover preference risk assessments of four South-Central US milkweeds (Asclepias spp.) important for monarch butterflies

“…We found from 6-31% of our milkweed occurrences were associated with roadsides in our study area, depending on the species. Management of roadside habitats is receiving increased focus for bene tting pollinator species in general (Hopwood et al 2015;Phillips et al 2020), and milkweeds and monarchs (Fischer et al 2015;Kasten et al 2016;Kaul and Wilsey 2019;Knight et al 2019;Cariveau et al 2019Cariveau et al , 2020Monarch CCAA/CCA Development Team 2020).…”

“…Waterbury et al (2019) found that A. speciosa, A. incarnata, and other Northwestern US milkweeds rarely utilized land covers of cultivated crops, developed, pasture/hay, and mixed and evergreen forest, and major habitat threats included invasive plants, herbicide use, and mowing. In comparison to data on A. syriaca in the Midwest (Hartzler 2010;Pleasants 2017;Kaul and Wilsey 2019) and A. speciosa in the Northwest, information is lacking on the utilization and risk of different LULC types for South-Central US milkweeds. We take a hierarchical approach (see Wilting et al 2010 and Online Resource 1 Introduction) to assess species land cover preference risk for milkweeds, rst de ning the core habitat of milkweeds using an ensemble of feature-selected MaxEnt niche models.…”