DOI: 10.5061/dryad.6t1g1jwv1
title: Intraspecific variation in body size of bumblebee workers influences anti-predator behavior

description: 1.Flower dwelling predators make flowers dangerous foraging sites for
 pollinators, potentially affecting their anti-predator behavior. Moreover,
 predation vulnerability often varies among pollinators’ body-sizes with
 interspecific comparisons showing that smaller species are more vulnerable
 than larger ones. However, how intraspecific body size variation
 influences pollinator behavior under predation risk is still unknown,
 especially under natural conditions. 2.We hypothesized that bumblebee
 workers of different sizes will exhibit different foraging strategies
 under predation risk. We predict that (i) small workers should more often
 exhibit anti-predator behaviors than larger workers. We also hypothesized
 that the anti-predator behavior should be influenced by predator size and
 reward availability, therefore we expect (ii) higher avoidance behavior
 towards larger predator sizes, and (iii) more and longer visits to
 inflorescences with high nectar availability. Finally, we expect that (iv)
 nectar availability should overcome the anti-predator behavior in less
 vulnerable, large, workers. 3.We recorded flower visitation, time spent
 and rejection behaviors of different sizes of Bombus terrestris (Apidae)
 workers (large, medium, and small) to inflorescences of Alstroemeria aurea
 (Alstroemeriaceae) with different treatments of artificial spiders (small
 and large) and nectar availability (with, without). 4.Anti-predator and
 foraging behavior of bumblebees was affected by the size of the worker,
 the presence of artificial spiders and nectar availability. Large and
 medium size bumblebees, strongly reduced flower visitation and time spent
 in the presence of artificial spiders, consistently avoiding flowers with
 spiders, regardless of spider size or nectar availability. Instead, small
 bumblebees seldom modified their behavior when facing artificial spiders,
 only increasing their avoidance or decreasing their foraging time in
 nectarless flowers hosting large artificial spiders. 5.This pattern of
 larger workers being more sensitive to predation risk than smaller ones at
 the intraspecific-level in B. terrestris is contrary to the expected and
 acknowledged trend based on previous interspecific comparisons, but
 partially consistent with predictions of models of optimal foraging
 theory. Intraspecific behavioral variability was uncovered only when
 nectar was available, whereas artificial predator size rarely modified
 bumblebee anti-predator and foraging behavior. Therefore, our findings
 suggest that the trade-off between maximizing resource intake and
 minimizing predation risk strongly varies across bumblebee worker body
 sizes.
description: To determine intraspecific variability in bumblebee responses to
 the presence of artificial spiders, we designed a fully crossed
 factorial field experiment with three factors:
 (1) predation risk with three levels (inflorescences without (Control),
 with a small (S) and with a large (L) artificial spider) and (2) nectar
 availability with two levels (with and without nectar), using 53 plants
 per treatment. In addition, (3) bumblebee workers body size was used as
 another factor with three levels: large, medium and small. We manipulated
 the amount of nectar in inflorescences by bagging them with a net that
 prevents insect visitation and enhances nectar accumulation, the day
 before the assay was carried out. Over the course of the flowering season,
 we bagged 159 plants from a total of 318 marked plants. The other group of
 159 plants was exposed to floral visitors the day before the assay was
 carried out. If remaining nectar was present we extracted it using
 microcapillaries, before the behavioral observations were made, to ensure
 contrasting nectar availability conditions. Each artificial
 spider was placed in one flower of the inflorescence and the behavior of
 arriving <i>B. terrestris</i> bumblebees were observed during
 10 minute periods.