Competition, Foraging Energetics, and the Cost of Sociality in Three Species of Bees

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Abstract
Competition among three species of bees (Apis mellifera, Bombus sonorus, and Xylocopa arizonensis) visiting Agave schottii was studied. Honeybees were found to predominate in the most productive habitats, Xylocopa in the least; Bombus as most abundant in patches of intermediate quality. It is suggested that these observations are consistent with a simple graphical model relating the standing crop of available nectar to foraging energetics and the additional costs of colonial life (cost of sociality). Temporal variations in foraging behavior were also observed, with Apis again preferring to forage at those times of day (early morning and late afernoon) when resources were most abundant. Bombus was less crepuscular than Apis, and carpenter bees foraged without obvious regard to variation in standing crop. Several factors which may account for this pattern are discussed.