| Abstrakt: |
Linear features are important landscape elements, providing a range of ecosystem services including pollination to adjacent crops and wild plants. Whilst many aspects of linear features have been shown to impact on resource use by wild pollinators, our principal aim was to explore the impact of topographical variation on the abundance and richness of bumblebee (Bombus) species. Disused railway lines, repurposed as recreational tracks, were used to explore the impact of topography using standardised bee transects through Cuttings (track bed below the surrounding landscape), Flats (track bed at the same level as the surrounding landscape), and Embankments (track bed above the surrounding landscape) (15 each) in the East Midlands of the UK during August 2012. We also recorded general site characteristics including Ordnance Survey grid references, track orientation, and width of vegetation alongside the track. We carried out quadrat surveys of ground flora and estimated flower abundance and canopy cover. Over 1500 individual bumblebees were recorded from 11 species. Bumblebee abundance was × 6.4 higher in Flats and × 8.6 higher in Embankments compared with Cuttings. Dunn multiple comparisons with Bonferroni correction following Kruskal–Wallis Anova showed significantly (P < 0.05) more bumblebees in total, for Bombus pascuorum, and for B. lapidarius in Embankments compared with Cuttings, but no significant differences (P > 0.05) in abundance between Embankments and Flats. Significantly more bumblebees were found in Flats compared with Cuttings for total bumblebees and B. pascuorum, but not for B. lapidarius. Cuttings had the lowest total number of species (4) compared with Flats (11) and Embankments (8). Median bumblebee species richness was significantly greater in Embankments and Flats compared with Cuttings, but no significant difference was evident between Embankments and Flats. Following model simplification, averaged negative binomial and Poisson glm models were created of bumblebee abundance and richness (respectively). Modelling indicated that the total abundance of bumblebees was significantly affected by track morphology, and also by the abundance of Thistle/Knapweed (Cirsium/Carduus/Centaurea spp.) flowers. Canopy cover by trees/tall shrubs negatively impacted on bumblebee abundance. Modelling of the dominant species (Bombus pascuorum) confirmed the importance of Thistle/Knapweed flowers and Morphology, but also identified an interaction effect of track Orientation for Embankments. Canopy cover was the only significant influence (negative) on bumblebee richness identified by modelling. The results are discussed in relation to the resources available to bumblebees in disused railway lines, the impact of topography on resources, the timing of the surveys and management implications. Implications for insect conservation: Our results show that disused railway lines can provide nectar resources for bumblebees. Further, the abundance and richness of Bombus species was modified by topographically-mediated impacts on vegetation (including shading and provision of nectar sources). Disused railway lines have the potential to provide a range of resources for insects in the wider countryside. [ABSTRACT FROM AUTHOR] |
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