title: Modeling the status, trends, and impacts of wild bee abundance in the United States.
abstract: Wild bees are highly valuable pollinators. Along with managed honey bees, they provide a critical ecosystem service by ensuring stable pollination to agriculture and wild plant communities. Increasing concern about the welfare of both wild and managed pollinators, however, has prompted recent calls for national evaluation and action. Here, for the first time to our knowledge, we assess the status and trends of wild bees and their potential impacts on pollination services across the coterminous United States. We use a spatial habitat model, national land-cover data, and carefully quantified expert knowledge to estimate wild bee abundance and associated uncertainty. Between 2008 and 2013, modeled bee abundance declined across 23% of US land area. This decline was generally associated with conversion of natural habitats to row crops. We identify 139 counties where low bee abundances correspond to large areas of pollinator-dependent crops. These areas of mismatch between supply (wild bee abundance) and demand (cultivated area) for pollination comprise 39% of the pollinator-dependent crop area in the United States. Further, we find that the crops most highly dependent on pollinators tend to experience more severe mismatches between declining supply and increasing demand. These trends, should they continue, may increase costs for US farmers and may even destabilize crop production over time. National assessments such as this can help focus both scientific and political efforts to understand and sustain wild bees. As new information becomes available, repeated assessments can update findings, revise priorities, and track progress toward sustainable management of our nation's pollinators.
authors.affiliation: Gund Institute for Ecological Economics, University of Vermont, Burlington, VT 05405; ikoh@uvm.edu.
authors.forename: Insu
authors.initials: I
authors.lastname: Koh
authors.affiliation: Gund Institute for Ecological Economics, University of Vermont, Burlington, VT 05405; Biology Department, Franklin and Marshall College, Lancaster, PA 17604;
authors.forename: Eric V
authors.initials: EV
authors.lastname: Lonsdorf
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, CA 95616;
authors.forename: Neal M
authors.initials: NM
authors.lastname: Williams
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, CA 95616;
authors.forename: Claire
authors.initials: C
authors.lastname: Brittain
authors.affiliation: Department of Entomology, Michigan State University, East Lansing, MI 48824;
authors.forename: Rufus
authors.initials: R
authors.lastname: Isaacs
authors.affiliation: Department of Entomology, Michigan State University, East Lansing, MI 48824;
authors.forename: Jason
authors.initials: J
authors.lastname: Gibbs
authors.affiliation: Gund Institute for Ecological Economics, University of Vermont, Burlington, VT 05405; Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington, VT 05405.
authors.forename: Taylor H
authors.initials: TH
authors.lastname: Ricketts
mesh_terms: D000818:Animals; D001516:Bees / Q000502:physiology*; D018556:Crops, Agricultural; D000067565:Farmers; D006801:Humans; D008954:Models, Biological; D054817:Pollination; D011157:Population Dynamics; D014481:United States
keywords: crop pollination; ecosystem services; habitat suitability; land-use change; uncertainty