DOI: 10.5061/dryad.rfj6q579h
title: Plant-pollinator interactions between generalists persist over time and space

description: Generalist species are the linchpins of networks, as they are important
 for maintaining network structure and function. Previous studies have
 shown that interactions between generalists tend to occur consistently
 across years and sites. However, the link between temporal and spatial
 interaction persistence across scales remains unclear. To address this
 gap, we collected data on plant-pollinator interactions throughout the
 flowering period for five years across six plots in a subalpine meadow in
 the Rocky Mountains. We found that interactions between generalists tended
 to persist more in time and space such that interactions near the network
 core were more frequently recorded across years, within seasons, and among
 plots. We posit that species’ tolerance of environmental variation across
 time and space plays a key role in generalization by regulating
 spatiotemporal overlap with interaction partners. Our results imply a role
 of spatiotemporal environmental variation in organizing species
 interactions, marrying niche concepts that emphasize species environmental
 constraints and their community role.
description: We conducted this study in a
 subalpine meadow at the University of Colorado’s Mountain Research Station
 (40°01'48" N, 105°32'26" W), located at 2900 m of
 elevation 22 km west of Boulder, CO, USA. The meadow faces east and is
 surrounded by aspen and spruce-fir forest. We collected interaction data
 weekly during the entire flowering period from 2015 to 2019. The flowering
 season at the study site typically starts after snowmelt in late May to
 early June and extends to late September. Interactions were recorded on
 16–18 weeks per year. We sampled on average 6.95 (±1.17 SD) days apart. On
 each sampling date, we sampled plant-pollinator interactions in six 20-30
 m × 2 m plots (five 30 m × 2 m and one 20 m × 2 m) by observing flowers
 (plant-centered sampling). Plots were at a similar elevation, 2962 -
 2978m. Sampling was conducted in fair weather during mornings between 8:00
 am and 12:00 pm, a time range when pollinator activity is high and before
 the onset of thunderstorms that often occur at mid-day during the summer
 in the Rocky Mountains. We sampled plant-pollinator interactions within
 each plot (in random order) by doing 15-min surveys in which we carefully
 observed all flowers for visitors while walking the periphery of plots to
 minimize trampling. When we observed an interaction, defined as a
 pollinator contacting the reproductive structures of a flower, we recorded
 the identity of the plant and pollinator species. Insect pollinators were
 collected with aspirators or aerial nets for later identification in the
 laboratory. Expert entomologists (see Acknowledgements) assisted with
 insects that are difficult to identify. We compiled all the observations
 from the study into a species x species plant-pollinator interaction
 matrix, sorting rows and columns to maximize binary nestedness. This
 sorting organizes plant species (top-to-bottom in rows) and pollinator
 species (left-to-right in columns) from most to least generalist according
 to their degree (number of partner species) such that generalist species
 are packed into the top left corner of the matrix. Using this matrix
 organization we created three matrices with cell values representing each
 variable of temporal or spatial persistence: the number of years, the span
 of days (phenophase, the maximum date minus the minimum date in which an
 interaction was recorded), and the number of plots in which interactions
 were recorded.