Neutral processes related to regional bee commonness and dispersal distances are important predictors of plant-pollinator networks along gradients of climate and landscape conditions
Cite this dataset
Sydenham, Markus Arne et al. (2022). Neutral processes related to regional bee commonness and dispersal distances are important predictors of plant-pollinator networks along gradients of climate and landscape conditions [Dataset]. Dryad. https://doi.org/10.5061/dryad.9w0vt4bjr
Understanding how niche-based and neutral processes contribute to the spatial variation in plant-pollinator interactions is central to designing effective pollination conservation schemes. Such schemes are needed to reverse declines of wild bees and other pollinating insects and to promote pollination services to wild and cultivated plants. We used data on wild bee interactions with plants belonging to the four tribes Loteae, Trifolieae, Anthemideae, and either spring- or summer-flowering Cichorieae, sampled systematically along a 682km latitudinal gradient to build models that allowed us to (a) predict occurrences of pairwise bee-flower interactions across 115 sampling locations, and (b) estimate the contribution of variables hypothesized to be related to niche-based assembly structuring processes (viz. annual mean temperature, landscape diversity, bee sociality, bee phenology, and flower preferences of bees) and neutral processes (viz. regional commonness and dispersal distance to conspecifics). While neutral processes were important predictors of plant-pollinator distributions, niche-based processes were reflected in the contrasting distributions of solitary bee and bumble bees along the temperature gradient, and in the influence of bee flower preferences on the distribution of bee species across plant types. In particular, bee flower preferences separated bees into three main groups, albeit with some overlap: visitors to spring-flowering Cichorieae; visitors to Anthemideae and summer-flowering Cichorieae; and visitors to Trifolieae and Loteae. Our findings suggest that both neutral and niche-based processes are significant contributors to the spatial distribution of plant-pollinator interactions so that conservation actions in our region should be directed towards areas: near high concentrations of known occurrences of regionally rare bees; in mild climatic conditions; and that are surrounded by heterogeneous landscapes. Given the observed niche-based differences, the proportion of functionally distinct plants in flower-mixes could be chosen to target bee species, or guilds, of conservation concern.
In 2017, we sampled flower-visiting bees at 115 sites in northern Germany, western Denmark, and southeastern Norway (Figure 1, Table 1). We sampled bees visiting plant species belonging to four tribes with morphologically distinct flowers and flowering times: White-petalled Anthemideae (Asteraceae) species; yellow-petalled Cichorieae (Asteraceae) species, which also differed in their flowering phenology, Cichorieae spring (Taraxacum spp.), or Cichorieae summer (e.g. Hieracium spp.); and two tribes of Fabaceae with zygomorphic flowers: Loteae species with yellow flowers and Trifolieae species with white to purple flowers. Species within these plant tribes attract a diverse community of bees (e.g. Rasmussen et al. 2016). The number of sampled plant types varied between sites, with one, two, and three types sampled at 92, 17, and 6 sites, respectively. Anthemideae were not sampled in Denmark as we were unable to find suitable locations. Site-pairs with between-site distances < 1000m could potentially share pollinators from the same populations (Greenleaf et al. 2007). We identified 76 clusters of sites within which between-site distances were < 1000m and between-cluster-distances were always >1000m, i.e. 76 statistically independent clusters. Of the 76 clusters, 50 contained one site, 17 contained two, six contained three, two contained four, and one cluster contained five sites.
At each site, we collected bees within an area of up to 50 by 50m, depending on the spatial distribution of the focal plant species. All bees were sampled by the first author. At each site, bee sampling was conducted once by collecting flower-visiting bees for 30 minutes on each plant type, adding 30 seconds of handling time per sampled bee. Sampling took place when the air temperature was > 15 °C and with little to no wind (Beaufort scale 0-3). Sampling followed onset of the flowering season, i.e., it started in northern Germany and ended in southeastern Norway (Table 1). All collected bees were stored in 96% ethanol prior to pinning and species identification. Voucher specimens are deposited in the entomological collection at the Norwegian Institute for Nature Research, Oslo.
The .csv table contains columns for:
- "Occurrence" = Presence or absence of bee-plant interactions
- "Interactions" = Number of bee-plant interactions
- "SiteID" = Identifier for the location where sample was conducted
- "SamplingDate" = Date sampling was conducted
- "Bee" = Bee species sampled on plant
- "PlantMrf" = Plant morph/tribe on which bees were sampled
- "RegionalCommonness" = regional commonness of bee species, estimated from GBIF occurrences
- "DistanceToSpecies" = distance to nearest known occurrence of bee species, estimated from GBIF occurrences
- "BIO1" = annual mean temperature, estimated from WorldClim dataset.
- "SH250m" = Shannon landscape diversity estimated at a 250m radius
- "SH1000m" = Shannon landscape diversity estimated at a 1000m radius
- "DCA1" = Bee floral preference score on detrended correspondence axis 1
- "DCA2" = Bee floral preference score on detrended correspondence axis 1
- "DCA3" = Bee floral preference score on detrended correspondence axis 1
- "DCA4" = Bee floral preference score on detrended correspondence axis 1
- "FirstMonth" = Bee phenology estimated as the first month of activity
- "Bombus" = categorical variable noting if bee species is solitary or belongs to the eusocial genus Bombus
- "ClusterID" = Cluster identity defining which cluster of sites a study belongs to
- "Longitude" = longitude in degrees (WGS84)
- "Latitude" = latitude in degrees (WGS84)
The Research Council of Norway, Award: 302692