Abstract
AbstractIn recent decades, many bumble bee species have declined due to changes in habitat, climate, and pressures from pathogens, pesticides, and introduced species. The western bumble bee (Bombus occidentalis), once common throughout western North America, is a species of concern and will be considered for listing by the U.S. Fish and Wildlife Service (USFWS) under the Endangered Species Act (ESA). We attempt to improve alignment of data collection and research with USFWS needs to consider redundancy, resiliency, and representation in the upcoming species status assessment. We reviewed existing data and literature on B. occidentalis, highlighting information gaps and priority topics for research. Priorities include increased knowledge of trends, basic information on several life‐history stages, and improved understanding of the relative and interacting effects of stressors on population trends, especially the effects of pathogens, pesticides, climate change, and habitat loss. An understanding of how and where geographic range extent has changed for the two subspecies of B. occidentalis is also needed. We outline data that could be easily collected in other research projects that would increase their utility for understanding range‐wide trends of bumble bees. We modeled the overall trend in occupancy from 1998 to 2018 of Bombus occidentalis within the continental United States using existing data. The probability of local occupancy declined by 93% over 21 yr from 0.81 (95% CRI = 0.43, 0.98) in 1998 to 0.06 (95% CRI = 0.02, 0.16) in 2018. The decline in occupancy varied spatially by landcover and other environmental factors. Detection rates vary in both space and time, but peak detection across the continental United States occurs in mid‐July. We found considerable spatial gaps in recent sampling, with limited sampling in many regions, including most of Alaska, northwestern Canada, and the southwestern United States. We therefore propose a sampling design to address these gaps to best inform the ESA species status assessment through improved assessment of how the spatial distribution of stressors influences occupancy changes. Finally, we request involvement via data sharing, participation in occupancy sampling with repeated visits to distributed survey sites, and complementary research to address priorities outlined in this paper.
Highlights
Many bumble bee species have recently declined in North America (Goulson et al 2008, Cameron et al 2011, Colla et al 2012, Arbetman et al 2017)
Literature review Because many life-history traits and stressors are common across bumble bee species, we build on the recent SSAs for rusty patched (Bombus affinis), yellowbanded (Bombus terricola), and Franklin bumble bees (Bombus franklini; Appendix S1)
We reviewed the literature using Google Scholar and Web of Science, with terms to target WBB
Summary
Many bumble bee species have recently declined in North America (Goulson et al 2008, Cameron et al 2011, Colla et al 2012, Arbetman et al 2017). Four of the five North American species in this subgenus have been or are planned for consideration for listing under the U.S Endangered Species Act (ESA) by the U.S Fish and Wildlife Service (USFWS). Three of the four species in Canada have been assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and are listed or recommended for listing under the federal Species At Risk Act (SARA; Appendix S1). The distribution and abundance of the western bumble bee (Bombus occidentalis, hereafter WBB) rapidly declined in recent decades (Cameron et al 2011, COSEWIC 2014). In the United States, a species status assessment, a best-availablescience summary that serves as the foundation for ESA listing decisions in the United States, is planned for WBB late in 2020, targeting a listing decision for 2023
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