Exotics on exotics: Pollen analysis of urban bees visiting Sedum on a green roof

• Published in: Urban ecosystems Vol. 18; no. 2; pp. 419 - 430
• Main Authors: MacIvor, J. Scott, Ruttan, Ally, Salehi, Baharak
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-06-2015; Springer Nature B.V
• Subjects: Bees; Biodiversity; Biomedical and Life Sciences; Design; Ecology; Environmental Management; Flowers & plants; Green buildings; Green roofs; Habitats; Horticulture; Introduced plants; Investigations; Irrigation; Life Sciences; Nature Conservation; Nesting; Plant reproduction; Pollen; Pollinators; Roofing; Studies; Urban areas; Urban Ecology; Vegetation; Toronto Ontario Canada; Canada; Native; Extensive; Urban; Habitat design; Diversity; Vegetated roof; Enhancement; Pollination
• ISSN: 1083-8155; 1573-1642
• DOI: 10.1007/s11252-014-0408-6

Numerous bee species were collected from a single green roof over the blooming period of the dominant exotic plant type,
Sedum
, a succulent stonecrop widely used in the green roof industry. As green roofs become more common in cities, an understanding of the potential positive and negative impacts of widespread use of this exotic but useful plant is needed. In this study we sampled bees visiting a green roof in downtown Toronto and compared the proportion of
Sedum
pollen in the loads they were carrying back to nesting locations. It was found that smaller bees (e.g.
Lasioglossum, Hylaeus
) were significantly less common on the roof compared with medium (e.g.
Apis
,
Megachile
) and large-sized bees (e.g.
Bombus
,
Andrena
). The proportion of
Sedum
pollen in the pollen loads of foraging bees collected was high amongst all bees (average of 80.5 % of total pollen load), but significantly greater for exotic bees compared to native bees. Moreover, native bees had significantly greater numbers of non-
Sedum
pollen types comprising more than >20 % of their pollen loads, meaning bees could be visiting flowers at ground level and on the roof in the same foraging bout. As the number of green roofs in cities increase, the characteristics of their designs, including the vegetation type and diversity, could have a significant impact in shaping local urban bee communities.