Abstract Detail

Ecology

The location of the rare Pitcher’s thistle (Cirsium pitcheri) along a dune community can influence weevil attack. Can it influence pollinators as well?

Pitcher’s thistle (Cirsium pitcheri) is a federally-threatened native plant and an important member of Lake Michigan sand dune ecosystems. Our previous research documented the dispersal patterns of invasive weevils at Whitefish Dunes State Park (Door County, WI) and found a strong preference by seed-eating weevils for C. pitcheri located in low-elevations of the sand dune landscape relative to those located at the top of the dune. The purpose of the study was to examine the spatial patterns of pollinating insect visits to Pitcher’s thistle plants throughout the Whitefish Dunes landscape and determine the factors that predict healthy seed-dispersal success. Over the course of four weeks of peak flowering, sixty-eight separate 45-minute pollinator observations were made on a total of 48 flowering C. pitcheri plants throughout the dune landscape. Observations were made simultaneously at high and low elevations using tripod-mounted GoPro cameras, along with human observers. The observer(s) noted the time of day, flower stage, weather, number of pollinators, and length of visit. Pollinators were identified to family or genus by visual ID. In August, we took a final assessment of inviable seeds from flower heads that failed to open. Our results suggested that pollinators did not show a general preference for thistles located at high or low dune elevations. There was no difference in the mean number of pollinator visits per observation period to plants located at high elevations and those located at low elevations (t = 1.99, P = 0.58). Likewise, there was no significant difference between elevations in the average species richness of pollinators (t = 1.99, P = 0.52) and duration of time pollinators visited flowers (t = 2.0, P = 0.49). These results contradict those of weevils which continued to infest flowerheads at lower elevations at significantly higher rates than those at the top of the dune, affecting seed viability. Our finding that dune elevation did not strongly influence pollinator visits is good news for Pitcher’s thistle conservation. This indicates that high-dune habitat may be refuges for C. pitcheri seed production and should be a focus of conservation efforts. We recommend that spotted knapweed be removed from this high-dune habitat at Whitefish Dunes to provide more opportunity for Pitcher’s thistle seed establishment.

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Keywords:
pollinators
elevational gradient.

Presentation Type: Oral Paper
Session: ECO7, Ecology 7: Species Interactions
Location: Virtual/Virtual
Date: Friday, July 31st, 2020
Time: 2:00 PM
Number: ECO7007
Abstract ID:698
Candidate for Awards:None