DOI: 10.5061/dryad.stqjq2c4m
title: Wildfire severity alters drivers of interaction beta-diversity in plant-bee networks

description: Spatial variation in species interactions (interaction β-diversity) and
 its ecological drivers are poorly understood, despite their relevance to
 community assembly, conservation, and ecosystem functioning. We
 investigated effects of wildfire severity on patterns and four proximate
 ecological drivers of interaction β-diversity in plant-bee communities
 across three localities in the Northern Rocky Mountains (Montana, USA).
 Wildfires decreased interaction β-diversity but increased interaction
 frequency (number of visits) and richness (number of links). After
 controlling for interaction frequency and richness, standardized effect
 sizes of interaction β-diversity were highest following mixed-severity
 wildfires, intermediate following high-severity wildfires, and lowest in
 unburned landscapes, suggesting that wildfire increases spatial
 aggregation of plant-bee interactions. Moreover, higher effect sizes in
 burned landscapes were largely determined by turnover in the species
 composition of both trophic levels rather than by interaction rewiring
 (spatial turnover in local species interactions not due to species
 turnover). The underrepresented level of rewiring indicated spatial
 consistency in post-disturbance patterns of interactions among
 co-occurring species. Together, our findings suggest that wildfire alters
 the β-diversity of mutualistic species interactions via linked assembly of
 plant-bee communities and provide insights into how environmental change
 alters complex networks of species interactions.
description: We studied plant-bee interactions in three distinct
 localities—Helena (HE), Paradise Valley (PV), and Whitefish (WF)—in the
 Northern Rockies Ecoregion of Montana, USA. Study sites were selected to
 span mixed-severity fire (MX), high-severity fire (HI), and unburned areas
 (UN). We quantified plant-pollinator interaction networks at each site by
 observing floral visitors at open flowers in a 25 m diameter plot (491
 m<sup>2</sup>) weekly for 20 min during times of greatest
 visitor activity (sunny, calm, 0900-1600) over the growing season
 (late-May – August, depending on the locality). Pollinators were those
 floral visitors contacting the reproductive parts of flowers and moving
 among flowers, and we captured them with hand nets. Plant and floral
 visitor species presence at a site was determined by their participation
 in at least one plant-pollinator interaction. We did not consider plant
 species with flowers that were never visited. Plots in Helena were
 observed twice in 2013, 12 times in 2014, 9 times in 2015, and 7 times in
 2016. Plots in Paradise were observed twice in 2013, 9 times each in 2014
 and 2015, and 5 times in 2016. Plots in Whitefish were observed twice in
 2013 and 7 times each in 2014 and 2015 (Burkle et al. 2019). Floral
 visitors were frozen, pinned, and identified to species. Because bees were
 89% of individual visitors to flowers, we focused on this group and pooled
 plant-bee interactions for each site across all observations for
 analyses.
description: INTERACTION_FREQUENCY refers to the number of time we observed
 bees of a particular species (BEE_SPECIES) visiting flowers of a
 particular plant species (FLOWER_SPECIES) at that site.