Western Bumble Bee: Declines in the Continental United States and Range-Wide Information Gaps

In 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

The Effects of Biogeography on Ant Diversity and Activity on the Boston Harbor Islands, Massachusetts, U.S.A

Many studies have examined how island biogeography affects diversity on the scale of island systems. In this study, we address how diversity varies over very short periods of time on individual islands. To do this, we compile an inventory of the ants living in the Boston Harbor Islands National Recreation Area, Boston, Massachusetts, USA using data from a five-year All Taxa Biodiversity Inventory of the region's arthropods. Consistent with the classical theory of island biogeography, species richness increased with island size, decreased with island isolation, and remained relatively constant over time. Additionally, our inventory finds that almost half of the known Massachusetts ant fauna can be collected in the BHI, and identifies four new species records for Massachusetts, including one new to the United States, Myrmica scabrinodis. We find that the number of species actually active on islands depended greatly on the timescale under consideration. The species that could be detected during any given week of sampling could by no means account for total island species richness, even when correcting for sampling effort. Though we consistently collected the same number of species over any given week of sampling, the identities of those species varied greatly between weeks. This variation does not result from local immigration and extinction of species, nor from seasonally-driven changes in the abundance of individual species, but rather from weekly changes in the distribution and activity of foraging ants. This variation can be upwards of 50% of ant species per week. This suggests that numerous ant species on the BHI share the same physical space at different times. This temporal partitioning could well explain such unexpectedly high ant diversity in an isolated, urban site

Relationships between forest-floor invertebrate distribution, movement, and microclimate under alternative riparian management practices

Headwater streams and their riparian zones are a common, yet poorly understood, component of Pacific Northwest landscapes. I sought to describe the ecological significance of headwater stream riparian zones as habitat for forest-floor invertebrate communities, and to assess how alternative management strategies for riparian zones may impact these communities. I compared community composition of forest-floor invertebrates at five distances along 70 m trans-riparian (stream edge to upsiope) gradients in three treatments: mature forests; clearcuts; and across riparian buffers of ~30 m width. In the buffer treatments, I looked for evidence of microclimatic edge effects, and also biological edge effects, as characterized by species distribution and movement patterns across the forest-clearcut boundary. Invertebrates were collected in pitfall traps, in five replicate blocks of three treatments each, in the Willamette National Forest, OR. Air and soil temperature, and relative humidity were measured at a subset of pitfall locations at each site. A pitfall grid was installed at one riparian buffer site for a mark-release- recapture study to record carabid beetle and lycosid spider movements across the buffer edge. Ordination revealed a distinct "riparian" invertebrate community within 1 m of the stream edge in mature forest treatments, which was strongly related to a cool, humid microclimate. The stream appeared to influence microclimate at least 20 m up slope in the mature forest treatments. Invertebrate community composition in buffer treatments was far more similar to that of mature forests than was that of clearcuts, a pattern mirrored by microclimate. Microclimatic edge effects were not evident in the buffer, suggesting that the stream's cool, humid influence on microclimate may be modifying any warm, drying effects coming in from the forest-clearcut edge. While biological edge effects were not clear for invertebrate communities, individual species showed various responses to the buffer edge, depending on their habitat affinities and mobility. These results suggest that invertebrate distributions are strongly associated with microclimate, and that riparian buffers of ~30 m width provide suitable habitat for many forest species. However, buffer edges may serve as barriers to dispersal for some forest interior species, or be permeable to invasion by open-habitat species, with possible consequences for long-term population and community dynamics within the buffer

Arthropod communities along an elevation gradient in Denali National Park and Preserve, Alaska: Rapidly shrinking tundra hosts a unique assemblage of specialists

ABSTRACTArthropods at high latitudes and elevations are likely to be vulnerable to effects from climate change such as increased temperatures and shifting vegetation boundaries. Though range shifts northwards and upslope have been reported for many arthropod taxa in temperate latitudes, baseline data needed to track such changes are scarce at northern latitudes. We investigated the influence of climate and vegetation cover on the abundance, diversity, and species composition of pollinators and epigeic arthropods along an elevation gradient in Denali National Park and Preserve, Alaska. We compared arthropods across three habitat types: low-elevation forest, mid-elevation shrubs, and high-elevation tundra along five replicate transects over three years. We collected 35,473 arthropods representing 510 species. Arthropod communities differed distinctly across the three habitat types, with tundra having the highest number of strong indicators and unique species. Elevation, air temperature, and vegetation structure were strong drivers for the ordination of sites. As treeline and shrubline shift upslope with climate change, we predict that distributions of some arthropods will shift to track these habitat boundaries and that tundra-associated arthropods will be most vulnerable as their habitat shrinks. Long-term monitoring of arthropods along elevation gradients at northern latitudes is needed to detect such declines

Appendix A. Functional role, overall abundance, frequency, and mean abundance of invertebrates between 1 and 20 m from the stream in three management treatments.

Functional role, overall abundance, frequency, and mean abundance of invertebrates between 1 and 20 m from the stream in three management treatments