The variability of bee communities along an urban gradient has a potentially strong impact on pollinator-plant interactions. We investigated changes in bee species richness and community composition in the city centre and suburbs of Poznań, Poland. During 2006-2008 we recorded 2,495 individuals from 104 species. The most abundant species was Andrena haemmorhoa. Other abundant species were Bombus pascuorum, Andrena vaga, Andrena nitida, Bombus terrestris. Several species appeared to be more abundant in the city centre whereas others showed an opposite tendency. We have found that the urbanized landscape can act as a filter for the bee community since some specific ecological traits facilitate colonization of the city centre. Small-bodied species that start their activity later in the season and are not solitary preferred the city centre. However, bee species diversity and richness remained stable across the urban gradient indicating some advantages of being a city dwelling bee. We suggest that a city can be a very important habitat for a diverse bee fauna and that conservation of a wide range of habitats of different urbanization levels seems to be the most suitable strategy for conservation of bee diversity in cities.

Urbanisation is an expansive process and a majority of insects live in human-modified areas. At the same time, a decrease in pollinator species richness and abundance has recently been observed in Europe, which in turn may have serious ecological and economic consequences. This study investigates the abundance, species richness and functional traits of wild bees in urban city parks in comparison to natural areas. The aim of this research was to assess the potential conservation values of urban green areas for bees. The present study demonstrates that a large and diversified city park may be a favourable habitat for bees, comparable to the natural fauna both in terms of the number and abundance of bee species. However, the study also showed that there were differences in the occurrence of species with different functional traits in the city parks investigated and in the natural landscape.

1. Urban ecosystems create suitable habitats for many plant and animal species, including pollinators. However, heterogenic habitats in city centres and suburban areas have various effects on pollinators due to variations in the composition of vegetation and in landscape management by humans.2. This study compared the abundance and species richness of three main groups of pollinators -wild bees, butterflies, and hoverflies -in Poznań, western Poland, and in three different types of urban green areas -urban grasslands, urban parks, and green infrastructure in housing estates.3. The total abundance of pollinators was higher in urban grasslands than in housing estates and urban parks. Species composition of pollinator communities differed between the three habitat types.4. The study results showed that species richness and abundance of butterflies varied between habitat types, whereas no such differences were found in the case of wild bees and hoverflies. Cover of green area, vegetation structure, and plant height were important for the pollinator community; however, these variables had different effects depending on habitat type. 5. These findings revealed that not all urban green areas are equally valuable in terms of local biodiversity. High-quality urban habitats such as urban grasslands are capable of supporting rich and abundant populations of pollinators. Therefore, it is important to protect high-value urban green areas and simultaneously strive to improve intensively managed urban habitats through effective planning and new management practices.

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Urban wastelands are important substitute habitats for many insect species, but their value for the protection of wild bees is still poorly studied. We assessed species richness, abundance, and the diversity of wild bees in wastelands that differed in area (2-35 ha), stage of ecological succession, location (suburbs or closer to the city centre), and history of land use. In the investigated plots, we recorded 42% of all bee species reported from Poland. The attractiveness of wastelands was positively correlated with the coverage of blooming herbs, coverage of shrubs and low trees, and the area of the wasteland. An increase in isolation of the habitat patches, the percentage contribution of alien species, annuals, and low grasses (< 25 cm) negatively affected the diversity of Apiformes. Considering the history of land use, we found that the bees were most attracted to wastelands resulting from extractive industry (sand and clay pits), and grassy habitats located in the suburbs, e.g. at sites grazed earlier by sheep. Wastelands in areas directly influenced by the chemical industry were the least attractive to bees. Analyses of quantitative and qualitative similarity of bees in various habitat types showed that three habitat types were the most similar to grasslands in the suburbs (the least disturbed habitats): degraded grasslands located closer to the city centre, extraction pits, and old fields. The presented results indicate that urban wastelands, including some post-industrial sites, can be important secondary habitats for wild bees. Thus, proper management of urban natural resources should cover both the formally managed areas and the so-called unproductive spaces, which have been undervalued so far.