DOI: 10.5061/dryad.b23v8nn
title: Data from: Beta diversity and specialization in plant-pollinator networks along an elevational gradient

description: Aim: To assess whether the reduced nutritional resources available for
 pollinators due to plant community simplification along an elevational
 plant-diversity gradient changes pollinator niche breadth and richness.
 Additionally, we evaluated how body size and proboscis length of
 pollinators shifted along the gradient, and whether these changes were
 related to pollinator niche breadth. Location: An elevational gradient
 (2,350-3,520 m a.s.l.) on the oceanic high-mountain strato-volcano of El
 Teide (Tenerife, Canary Islands). Taxon: Flowering plant and pollinator
 species. Methods: We compared quantitative plant–pollinator networks along
 the plant-diversity gradient. We calculated a set of niche-based
 topological metrics that capture the degree of specialization, niche
 breadth and niche overlap. Furthermore, we obtained β-diversity measures
 and the proportion of replacement and richness components. Results: There
 was an overall decline in species richness of pollinators with increasing
 elevation. This decline was mainly driven by the loss of species along the
 elevational gradient, which conformed a nested subset pattern. The whole
 network showed less specialization, greater connectance and lower
 modularity towards the summit. At high elevations, pollinators were more
 generalized and less selective in their flower choice, showing a greater
 trophic niche breadth compared to pollinators at lower elevations. Mean
 body size of pollinators increased with elevation, and species body size
 and proboscis length were positively associated with the number of plant
 species visited. Main conclusions. Overall, results indicated that the
 elevational gradient filters pollinator species, probably according to
 their thermal tolerance and ability to exploit a wide range of trophic
 resources. The finding that pollinators become more generalized and
 opportunistic at higher elevations is a novel result, which may have
 implications for new research into how ecological networks vary over
 environmental gradients. From an applied perspective, our results
 highlight the importance of considering the spatial variation of species
 assemblages when aiming to construct functionally reliable interaction
 networks along environmental gradients.
description: LaraRomero_JBI_Pollination_NetworksStudy site The study was carried out along an elevational gradient on El Teide strato-volcano (3,718 m), within El Teide National Park (Canary Islands; 28º16’15’’N 16º38’21’’O). The area is influenced by a typical high-mountain climate with great thermal oscillations throughout the year (differences of c. 10ºC between maximum and minimum monthly average temperatures). The sites receive an annual precipitation of c. 370 mm, most of which falls during winter. Four sites at different elevations were selected on the South-East faces of the strato-volcano: Montaña Rajada (2,350 m), Montaña Blanca (2,730 m), Refugio de Altavista (3,300 m), and La Rambleta (3,520 m). Dry open sclerophyllous scrubland occurs above the tree line (ca. 2,000 m), with vegetation cover decreasing with elevation. Eleven entomophilous plant species were found along the gradient, all of them endemic to the Canary Islands. For monitoring of plant–pollinator interactions, we established four plots of approx. 1 Ha distributed along an elevational gradient at the study site. Flower-visiting animals were observed on the plant species from 15th May to 15th August, for two consecutive years (2014 and 2015), coinciding with the flowering of all plant species in the different elevational communities. The censuses were carried out between 9:00 and 19:00 h, avoiding the beginning and the end of the day, when there were usually low temperatures and little insect activity in this high mountain environment, and also avoiding windy days. All plant species were censused 7-8 hours per locality and year, throughout the flowering phenology of each plant species, to maximize the possibility of detecting different floral visitors. Each census lasted 15 minutes, during which the observer remained facing the plant, recording all insects contacting the flowers as well as, whenever possible, the number of flowers contacted per individual. The individual plants to be censused of each species were arbitrarily chosen at each elevation. We recorded a plant-pollinator interaction when an insect maintained contact with the reproductive organs of a flower for more than 1 second. Thus, all flower-visiting insects (hereafter, named pollinators) that feed on flowers were recorded, regardless of the efficacy of their visit. Insects were either identified in the field or collected for later identification in the laboratory. Insect collection was not performed simultaneously with sampling of plant-pollinator interactions, to avoid affecting the data on interaction frequency. During the entire study period, a total of 868 observation hours were spent during 57 observation days. README file contains abbreviations used for species.