Reproduction of Amorpha canescens (Fabaceae) and diversity of its bee community in a fragmented landscape

Abstract

Loss of insect pollinators due to habitat fragmentation often results in negative effects on plant reproduction, but few studies have simultaneously examined variation in the bee community, site characteristics and plant community characteristics to evaluate their relative effects on plant reproduction in a fragmented habitat. We examined the reproduction of a common tallgrass prairie forb, Amorpha canescens (Fabaceae), in large (>40 ha) and small (<2 ha) prairie remnants in Iowa and Minnesota in relation to the diversity and abundance of its bee visitors, plant population size, and species density of the forb flowering community. We found significant positive effects of the diversity of bees visiting A. canescens on percent fruit set at a site in both years of the study and in 2002 an additional significant positive effect of plant species density. Abundance of bees visiting A. canescens had a significant positive effect on percent fruit set in 2002, but was only marginally significant in 2003. In 2003 but not 2002, the plant species density at the sites had a significant negative effect on the diversity and abundance of bees visiting A. canescens, indicating community-level characteristics can influence the bee community visiting any one species. Site size, a common predictor of plant reproduction in fragmented habitats did not contribute to any models of fruit set and was only marginally related to bee diversity one year. Andrena quintilis, one of the three oligolectic bee species associated with A. canescens, was abundant at all sites, suggesting it has not been significantly affected by fragmentation. Our results show that the diversity of bees visiting A. canescens is important for maintaining fruit set and that bee visitation is still sufficient for at least some fruit set in all populations, suggesting these small remnants act as floral resource oases for bees in landscapes often dominated by agriculture.

An assessment of pollen limitation on Chicago green roofs

“…Habitat patch size may not affect pollinator diversity or fruit set of prairie plant species growing in fragmented landscapes (Slage & Hendrix, 2009); even small patches of habitat such as that provided by green roofs, have the potential to provide the floral resources necessary to support pollinators. However, caution must be taken when applying the observed trends too broadly, as pollen limitation of a small number of individuals does not necessarily imply pollen limitation at larger population-level scales (Ashman et al, 2004).…”

The Role of Resources and Risks in Regulating Wild Bee Populations

“…Declines in populations of bee species other than honey bees, however, have been reported from several countries (6,22). While maintenance of bee abundance assures the continuation of pollination services, bee diversity can improve reproduction in individual crop (41,47,119) and wild plant species (37,105). Evidence also supports the positive role of pollinator diversity in maintaining plant community diversity (32).…”

Prairie restorations and bees: The potential ability of seed mixes to foster native bee communities

“…Restorations that improve pollinator diversity are increasingly important in promoting the success and stability of ecosystems (Winfree, Williams, Gaines, Ascher, Kremen 2008;Potts, Biesmeijer, Kremen, Neumann, Schweiger et al 2010;Garibaldi, Steffan-Dewenter, Winfree, Aizen, & Bommarco et al 2013) because of declines in bumble bees (Cameron, Lozier, Stange, Koch, Cordes et al 2011) and other native bees (Burkle, Marlin, & Knight 2013) (but see Bartomeus, Ascher, Gibbs, Danforth, Wagner et al 2013). Reciprocally, pollinator diversity can help support the success of prairie restorations by providing pollination services to native flowering forbs (Slagle & Hendrix 2009) and to important agricultural products (Winfree et al 2008). Thus, pollinators that visit and use restored sites will be important to long-term maintenance of plant diversity and community structure.…”