Does intraspecific size variation in bumblebees allow colonies to efficiently exploit different flowers?

Abstract

1. It has long been known that foraging bumblebee workers vary greatly in size, within species, and within single nests. This phenomenon has not been adequately explained. Workers of their relatives within the Apidae exhibit much less size variation.2. For the bumblebee Bombus terrestris size, as measured by thorax width, was found to correspond closely with tongue length, so that larger bees are equipped to feed from deeper flowers.3. The mean size of worker bees attracted to flowers was found to differ between plant species, and larger bees with longer tongues tended to visit deeper flowers.4. Finally, handling time depended on the match between corolla depth and tongue length: large bees were slower than small bees when handling shallow flowers, but quicker than small bees when handling deep flowers.5. Size variation within bumblebees may be adaptive, since it enables the colony as a whole to efficiently exploit a range of different flowers. Possible explanations for the marked differences in size variation exhibited by bumblebees compared with Apis species and stingless bees (Meliponinae) are discussed.

Bumble bees show trait-dependent vulnerability to landscape simplification

“…We thus expect to find fewer individuals of species with long proboscis in simple landscapes. (3) Variation in morphological traits may be substantial (Goulson et al 2002;Inoue and Yokoyama 2006;Peat et al 2005). Such variation could reflect niche breadth, such that the foraging work force from a colony with higher phenotypic variability can exploit a broader niche.…”

“…E.g. high variation in both proboscis length (Heinrich 1979, p. 29) and body size (Peat et al 2005) within a colony may increase the number of flower morphologies efficiently handled per colony, which could be more advantageous in complex landscapes containing a higher species richness of flowering plants. In addition, variation in body size may increase niche breadth by affecting variation in correlated traits such as flight speed and the ability to transport nectar (Goulson et al 2002) and foraging distance (Greenleaf et al 2007).…”

Evidence for competition between honeybees and bumblebees; effects on bumblebee worker size

“…Our data are not able to demonstrate a population-level effect, but it seems probable that if worker size is reduced that there would be effects on nest reproduction. Large workers collect more food per unit time than do their smaller sisters (Goulson et al 2002;Peat and Goulson 2005), in part because large workers have higher visual acuity and so are better able to swiftly locate floral resources (Spaethe and Weidenmuller 2002), and perhaps also because they are better able to forage in cool weather (Peat et al 2005b). Hence a nest with smaller workers is likely to have a reduced food supply and so produce fewer or smaller reproductives.…”

Decreasing worker size diversity does not affect colony performance during laboratory challenges in the ant Temnothorax nylanderi

“…To study the effects of continuous diversity on colony fitness and efficiency for particular tasks, researchers often focused on the function of larger and smaller workers in the colonies without manipulating worker diversity (e.g. Goulson et al 2002;Spaethe and Weidenmüller 2002;Peat et al 2005;Couvillon and Dornhaus 2010;Westling et al 2014). In order to test whether colony fitness is affected by colony-level worker size diversity, including the colony-level emerging properties of worker size diversity and not only the functions of large and small workers, we manipulated colonies to reduce worker size diversity in test colonies while natural diversity was retained in control colonies.…”