DOI: 10.5061/dryad.gb5mkkwwx
title: Wild bumblebees use both absolute and relative evaluation when foraging

description: Foraging theory assumes that animals assess value based on objective
 payoffs, however, animals often evaluate rewards comparatively, forming
 expectations based on recent experience. This form of evaluation may be
 particularly relevant for nectar foragers such as bumblebees, where
 individuals can visit thousands of flowers daily that vary in nectar
 quality. While many animals, including bees, demonstrate reference-based
 evaluation in experimental contexts, it is unclear whether this occurs in
 the wild. Here we asked how daily experience with wildflower nectar
 influenced wild bumblebees’ reward evaluation. We measured the daily
 nectar concentration of bee-visited wildflowers (Penstemon spp.), before
 presenting foragers with conspecific flowers filled with a range of
 artificial nectar concentrations. We recorded bees’ acceptance of
 artificial nectar, probability of subsequent visits to flowers on the same
 plant, and residence time. While bees had a minimum threshold of nectar
 acceptability that was unaffected by experience, when there was
 higher-concentration environmental nectar, they were less likely to accept
 lower-quality rewards on manipulated plants. Bees also visited more
 flowers and stayed longer on plants with higher-concentration nectar. This
 study shows evidence for both absolute and reference-based evaluation in
 wild bees and points towards differences between bees’ behavior in lab-
 and wild-foraging contexts.
description: We collected data in June 2021 at two sites in montane meadow and
 mixed conifer forests. The first site was in the Humboldt-Toiyabe National
 Forest (Dog Valley Meadow, California), which was lower elevation and
 bloomed earlier. The second site was in Tahoe National Forest (Van Norden,
 California). Experiments were conducted using the four most abundant
 species of bumblebee (n=180): <em>Bombus vosnesenskii
 </em>(n=88), <em>B. vandykei </em>(n=16)<em>, B.
 centralis</em> (n=52)<em>, B. vancouverensis nearcticus
 </em>(n=5). We focused on two flower species within the genus
 <em>Penstemon: P. rydbergii</em> at Dog Valley and
 <em>P. heterodoxus</em> at Van Norden. Each testing day, we
 calculated the average concentration of nectar in
 <em>Penstemon</em> in the study meadow, before offering
 foraging bumblebees <em>Penstemon</em> plants containing
 artificial nectar that varied across a range of concentrations. This
 allowed us to determine whether bees’ acceptance of nectar rewards varied
 based on their short-term foraging experience. To calculate wildflower
 nectar concentration, we collected nectar each day from 15-30 plants using
 1μl microcapillary tubes. These plants were bagged 24 hours earlier (when
 unopened) using white mesh organza drawstring bags (10 × 15 cm) to prevent
 visits from other insects prior to nectar extraction. Once nectar was
 extracted from all flowers on a plant, we cut plants at the base of the
 stem for use in behavioral experiments, using different plants for each
 bee. Following nectar extraction, we filled all previously-emptied flowers
 on each plant with 1 ml of a known sucrose solution of one of six
 concentrations (w/w): 0, 1, 5, 10, 25, and 50%. Once the bee landed on the
 manipulated plant, we recorded several behavioral responses. Namely, we
 stated the time that a bee landed on the plant, how many flowers she
 visited (typically via walking between flowers, but in one case the bee
 flew off the plant and then returned to another flower), whether she
 accepted or rejected the sucrose solution in each flower, and the time
 that she departed from the plant.
description: # Absolute and reference-based evaluation in wild bumblebees
 There are four annotated
 datasets: Fielddata.xlsx, field_data_accept.xlsx, field_data_visit.xlsx,
 nectar_data.xlsx ## Description of the data and file structure In
 Fielddata.xlsx, acceptance and visitation are coded as proportional data.
 This dataset was used to generate several of the main figures. Table of
 contents for field_data_visit * Column A: bee identity - factor * Column
 B: day number of experiment - continuous * Column C: date of data
 collection - factor * Column D: location of data collection - factor *
 Column E: time interval for data collection - continuous * Column F: time
 of day of data collection - continuous * Column G: experimental treatment
 concentration (%) - continuous * Column H: number of florets visited on
 previous flower - continuous * Column I: average number of florets visited
 on previous flowers - continuous * Column J: number of florets visited
 including revisits - continuous * Column K: number of florets filled -
 continuous * Column L: number of florets visited - continuous * Column M:
 number of florets visited including revisits - continuous * Column N:
 number of florets probed - continuous * Column O: number of empty florets
 probed - continuous * Column P: number of florets where nectar was
 consumed - continuous * Column Q: residence time on flower (s) -
 continuous * Column R: species of next flower visited - factor * Column S:
 average daily nectar concentration (%) continuous * Column T: species
 identification (factor) * Column U: inter-tegular distance (mm)
 -continuous Blank spaces in columns T and U indicate missing data for bee
 id or size. Columns V through X are the table of contents. In the two
 behavioral datasets, field_data_accept.xlsx and field_data_visit.xlsx,
 each behavioral response coded as a binary variable with a separate row
 corresponding to each behavioral observation. Table of contents for
 field_data_accept * Column A: bee identity - factor * Column B: day number
 of experiment - continuous * Column C: date of data collection - factor *
 Column D: location of data collection - factor * Column E: time interval
 for data collection - continuous * Column F: time of day of data
 collection - continuous * Column G: experimental treatment concentration
 (%) - continuous * Column H: visit number - continuous * Column I:
 acceptance - binary 0/1 * Column J: number of florets in which nectar was
 consumed - continuous * Column K: average daily nectar concentration (%) -
 continuous * Column L: species identification - factor * Column M:
 inter-tegular distance (mm) - continuous Table of contents for
 field_data_visit * Column A: bee identity - factor * Column B: day number
 of experiment - continuous * Column C: date of data collection - factor *
 Column D: location of data collection - factor * Column E: time interval
 for data collection - continuous * Column F: time of day of data
 collection - continuous * Column G: experimental treatment concentration
 (%) - continuous * Column H: number of florets filled - continuous *
 Column I: number or filled florets visited - continuous * Column J: number
 of florets visited including revisits to previously emptied florets -
 continuous * Column K: visit number - continuous * Column L: visit
 response - binary 0/1 * Column M: average daily nectar concentration -
 continuous * Column N: species identification - factor * Column O:
 inter-tegular distance (mm) - continuous Blank spaces in column L and M
 indicate missing data for bee id or size. Columns N through P are the
 table of contents. The last dataset, nectar_data.xlsx, contains daily
 nectar measurements for each day of the experiment at both locations. All
 datasets should be annotated with columns labeled. * Column A: date of
 data collection - factor * Column B: day of data collection - continuous *
 Column C: hour of data collection - continuous * Column D: nectar
 concentration measurement (%) - continuous * Column E: location of data
 collection - factor * Columns F through H are the table of contents. Links
 to other publicly accessible locations of the data: *
 ## Code/Software
 The R markdown file, Hemingway_et al.Rmd can be used to run all reported
 analyses and generate all published figures.