Floral resources, body size, and surrounding landscape influence bee community assemblages in oak‐savannah fragments

Abstract

1. Fragmentation of natural habitats due to urban development is predicted to have negative impacts on species diversity. The surrounding landscape (or 'matrix') of urban or semi-natural habitats can sometimes support biodiversity, but the amount of support will depend on species-specific traits, and on the resources available in the fragment and the matrix.2. Using data on bees collected from 19 oak-savannah fragments, the question of whether bee communities differ when fragments are embedded in different landscapes (Douglas-fir forest vs. urban residential neighbourhoods) was investigated, and also whether these differences could be attributed to species-specific traits of bees (e.g. body size, specialization) and/or within-fragment floral resources.3. No differences were found in overall richness or abundance of bees, but there were distinct differences in plant and bee community composition between matrix types. Common wood-nesters and late-flying, small-bodied bees tended to be found in urban-associated fragments, which also had a lower availability of within-fragment floral resources.4. Forest-associated fragments, on the other hand, had a greater density and richness of early-flowering native plant species, and supported a higher abundance of largebodied bee species. Bumble bee abundance, in particular, increased with increasing proportion of forest cover in the surrounding landscape.5. Large-bodied bees appear to respond to increased availability of within-fragment floral resources, but it was also hypothesised that nesting and floral resources in matrix habitat drive the differences in bee community assemblages.

Causes of variation in wild bee responses to anthropogenic drivers

“…It is therefore not surprising that different species show differential responses to the same anthropogenic drivers [19,20], and perhaps for this reason, also show different population trends over time [21 ]. Recent species-specific studies move beyond simply assessing how aggregate wild bee abundance or species richness is affected by anthropogenic drivers (Figure 1), which had been the focus of the literature previously [17,[22][23][24].…”

Flowering phenology and nesting resources influence pollinator community composition in a fragmented ecosystem

“…This distance captures the foraging range of most insect pollinators in this ecosystem (Wray et al 2014). Forest-associated OS fragments (N = 4) ranged from 34.28 to 51.48 % surrounding forest cover, while urban-associated OS fragments (N = 4) ranged from 0 to 4.0 % forest cover.…”

“…In landscapes with high variation in temporal and spatial distribution of floral resources, species may benefit by tracking the availability of resources in different landscape components over time Mandelik et al 2012;Tarrant et al 2013). For example, increased abundance and diversity of small-bodied generalist bees in natural habitat fragments surrounded by urban development is hypothesized to be due to use of floral resources in residential gardens in the urban matrix (Hinners et al 2012, Wray et al 2014, but this has not been explicitly tested. In contrast, floral specialists may not benefit from resources in the matrix, a hypothesis that could be evaluated if the matrix was included in sampling designs.…”

“…Previous research has shown that bumble bee abundance increases with more forest cover in the surrounding landscape, potentially due to increased availability of nesting resources (e.g. rodent holes, McFrederick and LeBuhn 2006) and/or earlyflowering food resources (Jha and Kremen 2013;Wray et al 2014). In order to conserve diverse, functioning communities across the landscape, studies should consider species-specific habitat requirements and whether natural and/or anthropogenic areas provide the resources they require.…”

Pan traps and bee body size in unmanaged urban habitats

“…Body size affects bee foraging behavior (Greenleaf et al 2007) and changes in this functional trait are increasingly used to understand how bee communities and species might respond to changes in landscape (Wray et al 2014, Renauld et al 2016). Herein we assess body size differences between bees captured at ground-level and elevated pan traps (70 cm) in unmanaged urban habitats in northwestern Turkey.…”