DOI: 10.5061/dryad.0rxwdbs2k
title: Data from: How far is enough? Prediction of the scale of effect for wild bees

description: A crucial issue for landscape ecologists is identifying the spatial
 extents at which a landscape affects species occurrence. Multi-scale
 analyses are usually conducted to identify the “scale of effect”, that is,
 the spatial extent associated with the best relationship between landscape
 variables and species occurrence, which is assumed to be related to
 species traits. However, few guidelines exist to determine the range of
 distances to be investigated. Based on the foraging distances of wild bee
 species, our main goal was to estimate the maximum distance of effect,
 that is, the distance beyond which the scale of effect for wild bee
 species is unlikely to be detected. Using the InVEST pollination model, we
 (i) modelled bee categories with distinct foraging distances and
 identified the scale of effect on their simulated abundance (ii) defined
 an index, noted λ, that estimates the distance beyond which landscape
 composition has only negligible effects on simulated abundances. We
 validated our results by identifying the scale of effect on the abundances
 of 16 bee species collected in south-western France. We detected a
 significant positive relationship between the average foraging distance
 (α) of the modelled bees and their scale of effect. The λ index was
 linearly related to the average foraging distances of bees (λ=5.4 α+253)
 and was above the identified scale of effect for the modelled bees. The λ
 was also found to be above the scale of effect for 93% of the observed bee
 species. Our results suggest that the λ index is a good estimator of the
 upper limit of the scale of effect for wild bees. The λ index could be
 used to identify the minimum distance between sampling sites before
 setting up an experiment and the maximum buffer size required in
 multi-scale analysis to detect the scale of effect.
description: Using the InVEST pollination
 model, we simulated the visitation rate of 16
 modelled bees that only differed in their average foraging distance
 (α-index), in 50 target sunflower fields located in south-western France
 in the Vallées et Coteaux de Gascogne site in 2016. The α-index ranged
 from 50 to 800 m with a 50-m increment. To assess the distance-weighted
 effects of landscape composition on the visitation rate of modelled bees
 we cropped the Land Use/Land Cover (LULC) input map around the centres of
 the 50 sunflower fields according to 108 different buffer radii (from 10
 to 90 m with 10-m increment and from 100 to 5 000 m with 50-m
 increment). In April 2016, we sampled bee species in 30
 sites (situated in the Vallées et Coteaux de Gascogne) with three coloured
 pan traps per sampling site. The traps were set up and left for four days
 and wild bee individuals were counted and identified to the species
 level. To identify the <em>scale of
 effect</em> for the 16 modelled bees and the 16 observed bee
 species, we performed multi-scale analyses with two landscape variables.
 The two landscape variables were (i) the mean availability of floral
 resources (in July for modelled bees, and in April for observed bee
 species), and (ii) the mean availability of belowground nests. These two
 variables were weighted means obtained by summing the indices of floral
 resource or nesting resource availability in each LULC category occurring
 around sampling sites within the 108 buffer radii.
description: Excel data files with (i) the visitation
 rates of 16 modelled bees in the 50 target fields and the mean
 availability of floral resources and mean availability of belowground
 nests according to 108 buffer radii, and (ii) the abundance of the 16 bee species
 collected in the 30 sampling sites (pan traps) and the mean availability
 of floral resources and mean availability of belowground nests according
 to 108 buffer radii.