DOI: 10.5061/dryad.80gb5mkt1
title: Raw data: Wildbee Monitoring along two elevational gradients in Germany

description: Global warming is assumed to restructure mountain insect communities in
 space and time. Theory and observations along climate
 gradients predict that insect abundance and richness, especially of
 small-bodied species, will increase with increasing
 temperature. However, the specific responses of single species to
 rising temperatures, such as spatial range shifts, may weaken such
 prediction, asking for intensive monitoring of real-world communities over
 time. Here, we examined the temporal and spatial change in wild bee
 communities and its drivers along two largely well-protected elevational
 gradients (alpine grassland vs. prealpine forest), each resampled within
 the last decade. Along both gradients, we detected clear upward shifts in
 bee communities, with cold-adapted bumblebee
 species reacting particularly sensitive, demonstrating the speed
 with which mobile organisms can respond to climatic changes. Mean annual
 temperature (MAT) was identified as the main driver of species richness in
 both regions. Accordingly, and in large overlap with expectations under
 climate warming, we detected an increase in bee richness and abundance,
 and an increase of small-bodied species in low- and mid-elevations along
 the grassland gradient. While changes in upward shifts, species richness,
 abundance and body size in the prealpine forest gradient were partly
 consistent with the alpine grassland system, they were generally weaker,
 which could be due to a much less severe warming trend than in the alpine
 grassland system or due to the variable and possibly confounding effect of
 canopy cover. Our study highlights the use of accurate
 assessed abundance data revealing rapid changes in bee communities over
 only one decade. We conclude, that in well-protected temperate regions,
 small-bodied bees may initially profit from warming temperatures, by
 getting more abundant and diverse.
description: The study was conducted along
 two elevational gradients in two different mountain ranges both located in
 south-eastern Germany: The first gradient was located in the National
 Park Berchtesgaden and vicinity, the so called Berchtesgadener Land (study
 region further referred to as BGL) and ranged from 641 m to 2032 m above
 sea level (m.a.s.l.).  In BGL, 33 grassland sites were selected (60 x 60
 m) along 5 mountain transects in 2009, of which 18 were extensively
 managed (grazed by cattle or sheep or mowed once in late summer) and 15
 were not managed (abandoned during the last century or above the
 treeline). Sites were resampled in 2019. In BGL, wild bees
 and honeybees were recorded from May to September thus encompassing
 approximately the full foraging season. Monitoring was conducted in
 standardized transect walks (10 evenly distributed sub-transects per site;
 duration of transect walk: 50 min (5 min per sub-transect)), six times in
 lower elevations (&lt;1200 m.a.s.l.) and due to a shorter season five
 times in higher elevations. Monitoring took place from 9:30 to 18:00 when
 the weather was sunny or when temperature at 650 m.a.s.l. was above 17°C
 on cloudy days. We used sweep nets to catch the insects. 
 The second prealpine forest
 gradient, ranging from 297 to 1368 m asl, was sampled along 4 transects
 within the Bavarian Forest National Park and in lowland plots (&lt;
 650 m.a.s.l.) outside the NP, which extended the elevational gradient down
 to the Danube River (further referred to BF). Here, 47 study sites were
 selected, which were first sampled in 2007 and 2008 and resampled in 2016.
 All sites were located within continuous forest or forest patches and
 varied in canopy cover as a measure of the summarized canopy cover of the
 tree layers and the shrub layer (range: 0- 180; with 0 = no forest; 300 =
 maximum possible density, details are described below). At elevations
 &gt; 1150 m asl this was primarily caused by windthrow events or bark
 beetle damage. The study region is dominated by mixed mountain forests of
 Norway spruce <em>Picea abies</em>, European
 beech <em>Fagus sylvatica</em> and silver fir <em>Abies
 alba </em>in the montane zone and mixed beech forests in lower
 elevations.In BF, wild bees and honeybees were recorded each
 month during May and September by deploying one flight-interception trap
 and one malaise trap on each site. While flight interception traps were
 activated over 4 weeks, malaise traps sampled over a period of 2 weeks
 each month. We further provide site information
 (elevation) including temperature data which was modeled from adjacent
 climate stations and data from the flowercover surveys for BGL and canopy
 cover per site data for BF.
description: Note that in BGL we recomment to summarise
 morphological very similar species <em>Bombus lucorum</em> and
 <em>Bombus terrestris </em>to <em>Bombus sensu
 stricto</em> complex due to field
 identifications.