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12/3/2018 Butterflies, Bees, and Weeds: Improving habitat for pollinators through management of Minnesotas tallgrass prairies Julia Leone , University of Minnesota, Conservation Biology Graduate Program Patrick Pennarola , University of

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Butterflies, Bees, and Weeds: Improving habitat for pollinators through management of Minnesota’s tallgrass prairies

Julia Leone, University of Minnesota, Conservation Biology Graduate Program Patrick Pennarola, University of Minnesota, Entomology Graduate Program Diane L. Larson, U.S. Geological Survey, Northern Prairie Wildlife Research Center Jen Larson, University of Minnesota Karen Oberhauser, University of Wisconsin, Madison Susan Galatowitsch, University of Minnesota

Why do we care about butterflies, bees, and weeds?

  • Pollinators are in decline worldwide
  • Minnesota prairies are home to several

imperiled bee and butterfly species

  • Weeds reduce native prairie plant diversity

and make it less fit as habitat for beneficial insects and grassland birds

How are tallgrass prairies managed?

Grazing and Fire

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Why manage Minnesota’s tallgrass prairie?

The wildfires and wide‐ranging herds of bison are no longer present

Why manage Minnesota’s tallgrass prairie?

Lacking fire and/or grazing, shrubs and trees would likely invade

John Metal

Ideal Management Outcome:

Butterflies Bees Weeds

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Where did we survey?

Data from MN DNR, US FWS; Jen Larson, 2016

  • 73 vegetation sites
  • Including 20 insect

sites

Private citizen partners

Butterflies

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How do butterflies depend on prairie habitat?

  • Nectar for adults
  • Larval host plants
  • Over‐wintering

shelters

How did we survey butterflies?

Pollard transect walk: Observer walk:

30 – 120 min.

  • All 5 families of Minnesota butterflies
  • 40 BUTTERFLY SPECIES
  • 9 prairie associated species
  • 1222 individuals

What butterflies did we find?

  • 35 species at burned prairies
  • 35 species at grazed prairies
  • 30 species were the same at

burned and grazed prairies

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Prairie Associated Species

Individuals at burned sites: 789 Individuals at grazed sites: 473

  • There are more butterflies at

burned sites

  • There are more common

species at burned sites

  • Many rarer species and

prairie specialists are found at grazed sites

Fire and Grazing management are both important for butterflies

Some butterflies were only found at grazed sites

Graze‐only

Silvery Checkerspot Broad‐winged Skipper Prairie Ringlet European Skipper Tawny‐edged Skipper

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Graze‐only Burn‐only

Reakirt's Blue Common Checkered‐ Skipper Arogos Skipper Acadian Hairstreak Edwards’ Hairstreak

and some butterflies were only found at burned sites

Silvery Checkerspot Broad‐winged Skipper Prairie Ringlet European Skipper Tawny‐edged Skipper

Regal Fritillary (Speyeria idalia)

David Wagner digginflowers

Regals at burned sites: 31 Regals at grazed sites: 12

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Bees

Bees globally are facing threats from habitat loss, pesticide exposure, and pathogens

How do bees depend

  • n prairie habitat?
  • Adult bees feed on nectar, and

provide larvae with pollen and nectar

  • Some bees nest in hollow stems
  • Many bees nest in soils

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Bee sampling methods

Bee sampling methods: Bee bowls and meandering walk

5m 20m 180m 30 min – 120 min

  • 121 bee species
  • 30 bee genera
  • 12,540 individuals
  • 11 species of bumble bees

What bees did we find?

  • 98 species at burned prairies
  • 94 species at grazed prairies
  • 71 species were the same at

burned and grazed prairies

  • B. auricomus
  • B. bimaculatus
  • B. terricola
  • B. vagans
  • B. pensylvanicus
  • B. borealis
  • B. ternarius
  • B. griseocollis
  • B. fervidus
  • B. impatiens
  • B. rufocinctus

1 2 3 4 5 6 7 8 9 10 Species distribution (no. sites)

Bumble bee species distribution

Burned Grazed Species occupancy (no. sites) Bumble bee species occupancy

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1 2 3 4 5 6 7 8 9 10 Species distribution (no. sites)

Bumble bee species distribution

Burned Grazed Species occupancy (no. sites) Bumble bee species occupancy

  • Slightly more bees were collected at

grazed sites than burned sites (6,491

  • vs. 6,039)
  • Very similar numbers of species (94 vs.

98)

  • Most species occur in both

managements

  • No significant difference, statistically,

in abundance or richness between burned and grazed sites

Grazing and fire are equivalent for bees

  • Higher frequencies of flowers in

prairies are significantly associated with greater numbers of bee species

  • Sandier soils are significantly

associated with greater numbers of bees and numbers of bee species

Beyond management: Other signals

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Colletes susannae

Graze‐only Burn‐only

Perdita perpallida Nomada articulata Svastra

  • bliqua

Heriades carinata Bombus rufocinctus Hylaeus nelumbonis Bombus rufocinctus Bombus terricola Megachile mendica

A subset of bees only found with one type or another

Plants

Does management with fire result in a different plant community than management with grazing?

  • No!
  • Sites closer together
  • n this graph had

more similar vegetation

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Weeds: Soil moisture is more important than management type

  • Canada thistle and Reed

canarygrass prefer wet prairie

  • Kentucky bluegrass and Smooth

bromegrass prefer mesic prairie

  • None showed a significant

preference for burned or grazed prairies

Canada thistle Burned Grazed Mean frequency

0.0 0.2 0.4 0.6 0.8 1.0

Kentucky bluegrass Burned Grazed Mean frequency

0.0 0.2 0.4 0.6 0.8 1.0

Mesic Wet Reed canarygrass Burned Grazed Mean frequency

0.0 0.2 0.4 0.6 0.8 1.0

Smooth Bromegrass Burned Grazed Mean frequency

0.0 0.2 0.4 0.6 0.8 1.0

Does prairie “quality” vary between management types?

 Mean species richness does not vary between management types.  Average richness:  24.39 in burned sites  24.47 in grazed sites  Coefficient of Conservatism is a measure of how restricted species are to high quality remnant prairie (higher=more restricted)  Average Coefficient of Conservatism  4.06 in burned sites  3.70 in grazed sites

We need both fire and grazing to improve habitat for prairie bees and butterflies

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Why do these results matter?

<1% remains

There is very little prairie left in Minnesota

  • Once 18 million acres
  • < 2% remains
  • Heavily fragmented

How are we sharing this information?

  • Direct feedback to participating

landowners and managers

  • Webinars
  • Workshop and field day for land managers
  • Public website
  • Public talks
  • Manuscripts in preparation

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Acknowledgements

Botanists: Karin Jokela, Katie Schmidt, Larissa Mottl, Madison Rancour Insect field assistant: Grant Piepkorn Lab technician: Grace Haynes USFWS, Morris WMD: Sara Vacek MN DNR: Fred Harris, Robert Dana, Crystal Boyd, Nicole Gerjets, site managers The Nature Conservancy Private Landowners Sam Droege, USGS

Thank you!

Questions? Diane Larson: dlarson@usgs.gov Julia Leone: leone050@umn.edu Patrick Pennarola: penna041@umn.edu

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