Dataset Information

Bumble bees (Bombus spp) along a gradient of increasing urbanization.

ABSTRACT:

Background

Bumble bees and other wild bees are important pollinators of wild flowers and several cultivated crop plants, and have declined in diversity and abundance during the last decades. The main cause of the decline is believed to be habitat destruction and fragmentation associated with urbanization and agricultural intensification. Urbanization is a process that involves dramatic and persistent changes of the landscape, increasing the amount of built-up areas while decreasing the amount of green areas. However, urban green areas can also provide suitable alternative habitats for wild bees.

Methodology/principal findings

We studied bumble bees in allotment gardens, i.e. intensively managed flower rich green areas, along a gradient of urbanization from the inner city of Stockholm towards more rural (periurban) areas. Keeping habitat quality similar along the urbanization gradient allowed us to separate the effect of landscape change (e.g. proportion impervious surface) from variation in habitat quality. Bumble bee diversity (after rarefaction to 25 individuals) decreased with increasing urbanization, from around eight species on sites in more rural areas to between five and six species in urban allotment gardens. Bumble bee abundance and species composition were most affected by qualities related to the management of the allotment areas, such as local flower abundance. The variability in bumble bee visits between allotment gardens was higher in an urban than in a periurban context, particularly among small and long-tongued bumble bee species.

Conclusions/significance

Our results suggest that allotment gardens and other urban green areas can serve as important alternatives to natural habitats for many bumble bee species, but that the surrounding urban landscape influences how many species that will be present. The higher variability in abundance of certain species in the most urban areas may indicate a weaker reliability of the ecosystem service pollination in areas strongly influenced by human activity.

SUBMITTER: Ahrne K

PROVIDER: S-EPMC2679196 | biostudies-literature | 2009

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Bumble bees (Bombus spp) along a gradient of increasing urbanization.

Ahrné Karin K Bengtsson Jan J Elmqvist Thomas T

PloS one 20090515 5

<h4>Background</h4>Bumble bees and other wild bees are important pollinators of wild flowers and several cultivated crop plants, and have declined in diversity and abundance during the last decades. The main cause of the decline is believed to be habitat destruction and fragmentation associated with urbanization and agricultural intensification. Urbanization is a process that involves dramatic and persistent changes of the landscape, increasing the amount of built-up areas while decreasing the a ...[more]

PMID: 19440367

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Project description:BACKGROUND:Despite the ecological and agricultural significance of bumble bees in Alaska, very little is known and published about this important group at the regional level. The objectives of this study were to provide baseline data on species composition, distribution, seasonal biology, and parasites of the genus Bombus at three major agricultural locations within Alaska: Fairbanks, Delta Junction, and Palmer, to lay the groundwork for future research on bumble bee pollination in Alaska. NEW INFORMATION:A total of 8,250 bumble bees representing 18 species was collected from agricultural settings near Delta Junction, Fairbanks, and Palmer, Alaska in 2009 and 2010. Of the 8,250 specimens, 51% were queens, 32.7% were workers, and 16.2% were males. The species composition and relative abundances varied among sites and years. Delta Junction had the highest relative abundance of bumble bees, representing 51.6% of the specimens collected; the other two locations, Fairbanks and Palmer represented 26.5% and 21.8% of the overall catch respectively. The species collected were: BombusbohemicusSeidl 1837 (= B.ashtoni (Cresson 1864)), B.balteatusDahlbom 1832, B.bifariusCresson 1878, B.centralisCresson 1864, B.cryptarum (Fabricius 1775) (=B.moderatusCresson 1863), B.distinguendusMorawitz 1869, B.flavidusEversmann 1852 (=B.fernaldaeFranklin 1911), B.flavifronsCresson 1863, B.frigidusSmith 1854, B.insularis (Smith 1861), B.jonellus (Kirby 1802), B.melanopygusNylander 1848, B.mixtusCresson 1878, B.neoboreusSladen 1919, B.occidentalisGreene 1858, B.perplexusCresson 1863, B.rufocinctusCresson 1863, and B.sylvicolaKirby 1837. Overall, the most common bumble bees near agricultural lands were B.centralis, B.frigidus, B.jonellus, B.melanopygus, B.mixtus, and B.occidentalis. Species' relative population densities and local diversity were highly variable from year to year. Bombusoccidentalis, believed to be in decline in the Pacific Northwest states, represented 10.4% of the overall specimens collected from the three sites studied. Bumble bees were found to be infected by Nosema and nematodes with infection rates up to 2.1% and 16.7% respectively. Of the eight species infected by parasites, B.occidentalis displayed the highest Nosema infection, while B.centralis was the species with the highest infection of nematodes. To our knowledge this represents the first multi-year study on bumble bees from the main agricultural areas of Alaska to provide baseline data on species composition, distribution, seasonal biology, and parasites of the genus Bombus.

Project description:BackgroundWild bees are important pollinators that have declined in diversity and abundance during the last decades. Habitat destruction and fragmentation associated with urbanization are reported as part of the main causes of this decline. Urbanization involves dramatic changes of the landscape, increasing the proportion of impervious surface while decreasing that of green areas. Few studies have investigated the effects of urbanization on bee communities. We assessed changes in the abundance, species richness, and composition of wild bee community along an urbanization gradient.Methodology/principal findingsOver two years and on a monthly basis, bees were sampled with colored pan traps and insect nets at 24 sites located along an urbanization gradient. Landscape structure within three different radii was measured at each study site. We captured 291 wild bee species. The abundance of wild bees was negatively correlated with the proportion of impervious surface, while species richness reached a maximum at an intermediate (50%) proportion of impervious surface. The structure of the community changed along the urbanization gradient with more parasitic species in sites with an intermediate proportion of impervious surface. There were also greater numbers of cavity-nesting species and long-tongued species in sites with intermediate or higher proportion of impervious surface. However, urbanization had no effect on the occurrence of species depending on their social behavior or body size.Conclusions/significanceWe found nearly a third of the wild bee fauna known from France in our study sites. Indeed, urban areas supported a diverse bee community, but sites with an intermediate level of urbanization were the most speciose ones, including greater proportion of parasitic species. The presence of a diverse array of bee species even in the most urbanized area makes these pollinators worthy of being a flagship group to raise the awareness of urban citizens about biodiversity.

Dataset Information

Bumble bees (Bombus spp) along a gradient of increasing urbanization.

Background

Methodology/principal findings

Conclusions/significance

Publications

Bumble bees (Bombus spp) along a gradient of increasing urbanization.

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