Bombus Mappers
Research Project
Executive Summary
Bumble bees (Bombus) play a significant role in the pollination of flora. They have a specialized buzz pollination technique that releases pollen from deep inside plant anthers that other pollinators cannot access, making them vital to the survival of many flora species. Several scientific studies conducted by educational institutions, and governmental and organizational entities, provide significant evidence that Bombus species populations have declined over the last several decades. To better understand this decline, and the severity and magnitude of contributing factors, it is necessary to investigate and assess their distribution and geographic locations. This type of research not only provides perspective regarding Bombus dispersal across landscapes, it can also inform strategies and potential policies that address their population decline and changing environments.
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This study provides insight into the geographic distribution and range of all 24 Bombus species native to Colorado. Analyzing both published and unpublished Bombus data helped determine if all 24 species still exist in Colorado, how each species is spatially distributed, and if any noticeable patterns exist in their distributions. Spatial analytical methods and heat maps provide these answers with a visual perspective of bumble bees and their potential habitats.
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The research results do not answer all the questions addressed here, but they do reveal spatial distribution patterns of individual species across specific regions of Colorado. A clear lack of data in the state's Eastern Plains and Southern region highlights the concentration of specimens found near universities and population centers. Of the 24 native Bombus species, 23 of them have high densities within Boulder and Larimer Counties from biases in data collection, as universities and research centers at these locations presumably have higher sampling efforts. Many species are found along Colorado’s Front Range and south along the Rocky Mountains, which is expected, as their habitats are largely found in high-elevation, mountainous alpine regions. To provide a more thorough distribution analysis of native Bombus species, it is recommended that sampling expeditions by universities and other local bee organizations be conducted over a more comprehensive area of Colorado, including grasslands and along river basins in the east, and particularly in areas experiencing environmental or anthropogenic transformations.
Overview of Methods
Colorado is home to a significant amount of Bombus diversity, 24 species in total, with species ranging in size, color, and habitat preferences. Colorado’s native bumble bees are found in various habitats, from high-elevation alpine meadows to lowland grasslands and urban gardens. Within these distinct environments, bumble bees are important pollinators for both native and cultivated crops.
This project examines the distributions of Colorado’s 24 native Bombus species at the sub-county level, and the statistical method of kernel density estimation was employed to determine these distributions. Kernel density estimation is a statistical technique used to estimate the probability density function of a continuous random variable. The results are calculated using historical data of Bombus species collections over a temporal period of over 100 years, which was then displayed on a series of heat maps showing the species distributions of Colorado’s 24 native Bombus species.
Results & Discussion
The answer to whether all 24 native Bombus species exist in Colorado is inconclusive due to a lack of data and limited collection ranges. Ultimately, collections that were too small, or ones found within only a few specific counties, are not necessarily fit for statewide analyses without wider collection efforts across under sampled regions. The analysis does however reveal several common spatial patterns among native Colorado Bombus species across the state, one of which is a clear lack of data collection in the Eastern and Southern regions of the state compared to Central, Northwestern, and Western regions. The Eastern Plains of Colorado are largely unpopulated and intensely farmed, and with majority of this portion of the state being flat and exposed, winds and extreme weather conditions make for this portion of the state to be unappealing for exploration. Majority of the concentration of species distribution occur in Boulder and Larimer County. While these counties are rich in resources for bumble bees along the Front Range, it should be noted that both counties are home to the University of Colorado Boulder and Colorado State University (Fort Collins), each of which conduct research on pollinators, creating a bias in the data. There are several patterns among individual species as well that lead to a recommendation to further sampling in these regions to understand distribution as well as determine if certain species are still present within Colorado.
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Conclusion
This research does not add to the increasing body of scientific evidence that native Bombus species are in decline in Colorado. It does, however, indicate that sampling efforts are nowhere near being equally represented across the state, and that areas not in close vicinity to universities or population centers are vastly undersampled. This can amount to erroneous distribution models that do not accurately assess how these native populations are responding to environmental changes caused by climate change, land use change, and other anthropogenic devices (Jamieson et al., 2019). There is still a great deal of work to do in order to achieve a complete native Bombus inventory in Colorado including large-scale landscape surveys in understudied regions, and producing higher quality datasets (Colla et al., 2016). Universities and others involved in bumble bee preservation could make a significant contribution to scientific research by not oversampling in areas historically acknowledged for having large Bombus populations, and expanding their collection efforts to a wider landscape