Effects of climate change-induced temperature variation on pollinator interactions of bumblebees (Bombus spp.) and a threatened dune thistle, (Cirsium pitcheri)

Project Overview
Project Abstract: 
Climate change is predicted to increase global average temperatures by 2-6 degrees by the year 2100. Increases in temperatures may cause increases in extreme heat events, which can alter important ecological interactions. Ecological mutualisms, such as those between plants and their pollinators, will likely be altered. Temperatures above the thermal tolerance of a pollinator species will prevent the normal functioning of individuals, consequently decreasing the success of both plants and pollinators. Listed or declining species are most at risk of the harmful effects of climate warming. One such plant is the federally threatened Pitcher's thistle, (Cirsium pitcheri), which is pollinated mainly by species of bumblebee, or Bombus. Pitcher's thistle is a rare dune plant that is endemic to the Great Lakes Region. Understanding the relationship between Pitcher’s thistle and its bumblebee pollinators is important for conservation of dune biodiversity. Few studies have quantified the thermal limits of bumblebee pollinators, none using all the bumblebee species commonly found in C. pitcheri habitat. The purpose of this study was to observe the community of bumblebee pollinators of C. pitcheri and to ask how this community changes relative to diurnal variation in air temperature in the face of climate change. To compare observations of the activity level of bumblebee species at various temperatures, the thermal range within which bumblebee species can maintain motor ability was experimentally determined.
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