Wildfire reveals transient changes to individual traits and population responses of a native bumble bee Bombus vosnesenskii

Positive impact of postfire environment on bumble bees not explained by habitat variables in a remote forested ecosystem

Bumble bees are important pollinators in temperate forested regions where fire is a driving force for habitat change, and thus understanding how these insects respond to fire is critical. Previous work has shown bees are often positively affected by the postfire environment, with burned sites supporting greater bee abundance and diversity, and increased floral resources. The extent to which fire impacts variation in bumblebee site occupancy is not well-understood, especially in higher latitude regions with dense, primarily coniferous forests. Occupancy models are powerful tools for biodiversity analyses, as they separately estimate occupancy probability (likelihood that a species is present at a particular location) and detection probability (likelihood of observing a species when it is present). Using these models, we tested whether bumblebee site occupancy is higher in burned locations as a result of the increase in canopy openness, floral species richness, and floral abundance. We quantified the impact of fire, and associated habitat changes, on bumblebee species' occupancy in an area with high wildfire frequency in British Columbia, Canada. The burn status of a site was the only significant predictor for determining bumblebee occurrence (with burned sites having higher occupancy); floral resource availability and canopy openness only impacted detection probability (roughly, sample bias). These findings highlight the importance of controlling for the influence of habitat on species detection in pollinator studies and suggest that fire in this system changes the habitat for bumble bees in positive ways that extend beyond our measurements of differences in floral resources and canopy cover.

Within-Year Effects of Prescribed Fire on Bumble Bees (Hymenoptera: Apidae) and Floral Resources

Despite the importance of bumble bees (genus Bombus Latreille) for their services to natural and agricultural environments, we know little about the relationship between grassland management practices and bumble bee conservation. Prescribed fire is a common grassland maintenance tool, including in areas where endangered and threatened bumble bees are present. Thus, knowledge of the effects of prescribed fire on bumble bees is essential for designing management schemes that protect and bolster their populations. Using nonlethal surveys to record bumble bee species richness, abundance, and community composition, we evaluated the effects of spring controlled burns on summer bumble bee gynes and workers across five sites in southern Wisconsin. In addition, we explored the effects of fire on floral resources by measuring floral genus richness, abundance, ground cover, and proportion of transects containing blooming flowers in adjacent burned and unburned parcels. Prescribed fire had no measurable effects on bumble bee gyne or worker community composition, species richness, or abundance. However, consistent with previous studies prescribed fire increased floral genus richness and ground cover. The disconnect between bumble bee and floral responses to fire highlights some opportunities for improving our understanding of fire's effects on bumble bee diapause, nest site choice, and foraging.

The Importance of Forests in Bumble Bee Biology and Conservation

Declines of many bumble bee species have raised concerns because of their importance as pollinators and potential harbingers of declines among other insect taxa. At present, bumble bee conservation is predominantly focused on midsummer flower restoration in open habitats. However, a growing body of evidence suggests that forests may play an important role in bumble bee life history. Compared with open habitats, forests and woody edges provide food resources during phenologically distinct periods, are often preferred nesting and overwintering habitats, and can offer favorable abiotic conditions in a changing climate. Future research efforts are needed in order to anticipate how ongoing changes in forests, such as overbrowsing by deer, plant invasions, and shifting canopy demographics, affect the suitability of these habitats for bumble bees. Forested habitats are increasingly appreciated in the life cycles of many bumble bees, and they deserve greater attention from those who wish to understand bumble bee populations and aid in their conservation.

Impacts of Fire on Butterfly Genetic Diversity and Connectivity

How do novel fire regimes and a long history of fire suppression influence species genetic diversity? Genetic diversity provides the raw materials for sustaining viable populations and for allowing adaptation to novel environmental challenges, and at present, few studies address the genetic responses of animals to fire management. Here we study the genetic responses of 2 butterfly species to a landscape gradient of fire timing and severity in Yosemite National Park using a large set of genome-wide single nucleotide polymorphisms (SNPs). Butterflies are important bio-indicators of invertebrate diversity and play important roles in both bottom-up and top-down ecosystem processes, and typically increase in abundance following wildfires, due to an increase in abundance of flowering plants. However, it is not clear how genetic diversity and genetic connectivity of butterflies respond to landscape change following fire, and whether fire management has positive or negative effects. We found evidence to suggest that fire increases genetic diversity and reduces isolation in 2 butterfly species, but that aspects of the fire regime (severity, extent, timing, and frequency) differ in importance depending on the ecology of the specific species. This research is the first study to address fire management impacts on genetic diversity in invertebrates, and the results will allow fire managers to predict that fire reintroduction in protected areas will generally benefit butterfly populations.