Habitat enhancements rescue bee body size from the negative effects of landscape simplification

Abstract

The negative effects of landscape simplification on bee communities are well documented. To reverse these effects, flowering habitat enhancements are designed to provide supplemental nutritional resources for wild bees and are particularly important when few resources are available in the surrounding landscape. Yet, it is not known whether or how habitat enhancements support bee populations under varying landscape contexts. Body size is a morphological trait that is strongly linked to foraging ability, immune function, and fitness in bees. Landscape simplification has been associated with size declines across bee taxa and smaller body size can be an early indicator of environmental stress. To determine whether the negative effects of landscape simplification on body size can be improved by adding floral resources to farm landscapes, we measured the body size of 10 wild bee species collected at 70 sites with or without habitat enhancements in Michigan and New York. Bees were collected at sites with varying amounts of agriculture in the surrounding landscape, allowing us to test whether morphological responses to enhancements are affected by landscape simplification. Half of the bee species measured exhibited declining body size across the landscape gradient. Among these species, declines were buffered by the presence of habitat enhancements suggesting this response is the result of improved nutrition, reduced need for long‐distance foraging, enhanced recruitment of larger individuals or a combination of these mechanisms. Declines in body size were strongest in both the smallest and the largest species. Large and medium sized species exhibited the greatest response to flowering habitat enhancements. Synthesis and applications. At sites with high agricultural cover, we observed intraspecific body size declines among many species; however, we did not observe decreased body size in any species at sites with a flowering habitat enhancement. Therefore, our findings suggest that the presence of flowering habitat enhancements can support wild bees experiencing stress from intensively managed agricultural landscapes across multiple cropping systems and regions.

Functional traits linked to pathogen prevalence in wild bee communities

“…In the field, bees experience numerous interacting stressors ( e.g. decreased floral diversity, increased pesticide exposure, and competition with honey bees 68 ), often being smaller in more simplified agricultural landscapes 69 – 72 . As such, we do not know if small individuals that were infected succumbed to the negative health consequence of the pathogens (and therefore were not out foraging for us to collect and screen), while larger individuals could tolerate the infections and thus bias the patterns.…”

Floral resource diversity drives bee community diversity in prairie restorations along an agricultural landscape gradient

“…It is also possible that the restorations themselves insulate bee communities from agricultural simplification. Recent work has shown that restorations improve bee community health through increased colonization and persistence (M'Gonigle, Ponisio, Cutler, & Kremen, 2015), higher intraspecific bee species body sizes (Grab et al., 2019) and increasing community heterogeneity in comparison to unrestored controls (Ponisio et al., 2017).…”

Human-Mediated Land Use Change Drives Intraspecific Plant Trait Variation

“…Previous work has emphasized the effects of land use change on whole communities, yet insect functional traits are also affected by land use change. In pollinators for example, land use change can decrease body size ( Persson and Smith, 2011 ; Renauld et al, 2016 ; Grab et al, 2019 ), which can negatively affect the pollination services provided to plants ( Jauker et al, 2016 ). While landscape mediated functional trait evolution is not well studied, we expect these trait expression shifts are present across insect groups and important in mediating insect interactions with plants.…”