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Grassland patches surrounded by less grassland contain more monarch butterflies compared to patches surrounded by more grassland.
However, egg + larva abundance was most related to the density of milkweeds.
MONARCH BUTTERFLY LANDSCAPE ECOLOGY:Effects of landscape and local patch characteristics on monarch abundanceAnna Skye Harnsberger¹, Karen Oberhauser¹, Wayne Thogmartin², Chris Trosen³, Claudio Gratton¹¹University of Wisconsin-Madison, ²United States Geological Service, ³United States Fish & Wildlife Service
PROBLEM• Loss of milkweed from the landscape.• ~1.8bil stems needed to sustain the
eastern migratory monarch population.
HOWEVER• Need to know how to optimize habitat
restorations for monarchs.• Does surrounding landscape influence
abundance of monarchs at a site?• How densely should stems be planted?• How big should plantings be?• Are many nectar species are needed?
PREDICTION• Patches with less surrounding grassland
will have higher monarch abundances.• Small patches with higher milkweed
density and more nectar plant species will contain more monarchs.
APPROACH• Surveyed 60 WI sites 3x each; 2018-19.• Measured monarch abundance, patch
size, milkweed density, nectar plants, landscape-level grassland.
• Multiple regressions including yr, region.
Figure 1 | Map of survey sites in Wisconsin.
ResultsTable 1 | Results from multiple regression models showing significance of each factor to each monarch life stage response metric. Symbols represent positive (+), negative (-), p≤0.001 (***), p≤0.005 (**), p≤0.05 (*), & p≤0.1(†) associations, and higher numbers (↑).
Figure 2 | Component-residual plots of factors with significant associations to monarch abundance.
Conclusions• If the goal of restoration is to see adult
monarchs, it should be placed within a site with less surrounding grassland on a 10km scale, rather than more. More nectar species are better than fewer. High milkweed density is important.
• If the goal of restoration is monarch recruitment, it is most important to plant a high density of milkweed stems.
• Abundance within a patch is not well predicted by the size of the patch; thus, milkweed plantings of any size could be beneficial to the monarch population.
Next Steps• Create mixed-effect models, treating site
survey time (early, mid, late summer) as a random effect.
• Model selection.
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Landscape grassland (proportion grassland within 10km, excluding grassland within 1km, standardized)
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Milkweed density(stems per m², standardized)
Milkweed density(stems per m², standardized)
Nectar plants(count, standardized)
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@LEPIDOPTERIST@GRATTONLAB
