Evidence of Bumble Bee Extirpation and Colonization, Galiano Island, British Columbia, Canada

Abstract

We present evidence for historical change in a bumble bee community on Galiano Island, British Columbia, Canada, including the probable extirpation of three bumble bee species-Bombus insularis Smith, B. occidentalis Greene, and B. suckleyi Greene-as well as the disappearance of two species represented by singletons in the historical record: B. fervidus Fabricius and B. flavidus Eversmann. Evidence is based on a comparison of historical and contemporary species occurrence data, including recent data from intensive sampling targeting bumble bees using blue vane traps. The decline of B. occidentalis in southern portions of its range has long been observed, yet to our knowledge this is the first established case of its probable extirpation within an extensively surveyed part of its range. Results indicate that an additional species, B. vosnesenskii Radoszkowski, is a recent arrival on Galiano Island and has been expanding its range concurrently with the decline of B. occidentalis. Elsewhere in the region B. vosnesenskii has become a dominant species, particularly in urban environments. However, our data show it to be the least abundant species on this largely forested island. We also report patterns in the occurrence of B. sitkensis Nylander and B. vosnesenskii, suggesting that niche segregation may confound the effect of competitive exclusion previously reported for these species. Potential factors contributing to this likely case of bumble bee extirpation and subsequent colonization are discussed in the context of Galiano Island's historical land use and ecology. In conclusion, we assess the potential for community science to aid in the detection of ecological change via comparison of historical baseline and contemporary crowd-sourced biodiversity data.