Is the city buzzing? Functional diversity of wild bees in an urban park.

Abstract

Wild bees are in decline, threatening the ecosystem functioning and pollination services that we are so dependent on. The rapid fragmentation and urbanisation are some of the major threats to the bee habitats, with deteriorating dietary resources and suitable nesting sites as some of the consequences. Quantifying functional traits is one important way of measuring biodiversity, instead of solely focusing on species richness. Therefore, the functional traits of the wild bee fauna found in the park Slottsskogen, Gothenburg, Sweden, were investigated and compared to two different rural areas with high nature values in two munici-palities on the Westcoast of Sweden: Borås and Mark. The functional traits were compiled through literature search, and tongue lengths, foraging distances and body sizes were estimated based on measured intertegular distances. The three different assemblages were then compared through a principal coordinate analysis. The traits making up most of the variation between the assemblages were whether or not the bees had pollen-carrying structures, their preferred pollen and nectar sources, what kind of habitat they choose to inhabit and if they nest aggregated or not. Nearly all bee species in Slottsskogen are polylectic, but the proportions of oligolectic bees were not significantly higher in Borås and Mark municipalities. The functional evenness and divergence within all three assemblages were high, but the functional richness of Slottsskogen was lower than both Borås and Mark municipalities. Comparing the beta diversity, the dissimilarity of the functional traits between Borås and Mark was low, and higher when Slottsskogen was compared to either of the two more rural assemblages. Slottsskogen is shown to be a sub-sample of the other two localities, indicated by a high nestedness coefficient, which suggests that the diversity differences are mainly due to dissimilarities in area size and nature types, and sampling methodologies. This is not to say that Slottsskogen is remarkably species-poor, given its circumstances. Nonetheless, to increase the functional diversity and richness of wild bees in a park like Slottsskogen, different measures are likely needed to enrich the dietary and nesting resources available, and the habitat diversity of the park.