Abstract
Pollinators are experiencing declines globally, negatively affecting the reproduction of wild plants and crop production. Well-known drivers of these declines include climatic and nutritional stresses, such as a change of dietary resources due to the degradation of habitat quality. Understanding potential synergies between these two important drivers is needed to improve predictive models of the future effects of climate change on pollinator declines. Here, bumblebee colony bioassays were used to evaluate the interactive effects of heat stress, a reduction of dietary resource quality, and colony size. Using a total of 117 colonies, we applied a fully crossed experiment to test the effect of three dietary quality levels under three levels of heat stress with two colony sizes. Both nutritional and heat stress reduced colony development resulting in a lower investment in offspring production. Small colonies were much more sensitive to heat and nutritional stresses than large ones, possibly because a higher percentage of workers helps maintain social homeostasis. Strikingly, the effects of heat stress were far less pronounced for small colonies fed with suitable diets. Overall, our study suggests that landscape management actions that ensure access to high-quality resources could reduce the impacts of heat stress on bee decline.
Highlights
Biotic pollination is essential for sustaining plant communities[1] and is an important ecosystem service[2], which is threatened by the ongoing global decline of pollinators[3]
It is expected that any negative impact caused by heat stress will be more accentuated when bees are subjected to nutritional stress
Its ability to regulate its internal body temperature is limited, which makes individuals sensitive to climate change including heat waves that have become more frequent across its native range in recent decades[34] and are likely to intensify in frequency and amplitude[18]
Summary
Biotic pollination is essential for sustaining plant communities[1] and is an important ecosystem service[2], which is threatened by the ongoing global decline of pollinators[3]. Interactive effects between climate and floral resources have rarely been addressed[30] but are important to consider given their implications and relevance to global change, especially under future climatic scenarios[18,31] To address these knowledge gaps, we used the buff-tailed bumblebee (Bombus terrestris) as a model organism and designed a fully crossed experiment (Fig. 1) to test the effect of (i) three distinct pollen diets displaying different amino acid concentrations and sterolic composition (i.e. low, medium and high suitability); (ii) three thermal regimes (i.e. control, short and long climatic stress); and (iii) two colony sizes (i.e. small and large colonies). We expect that low suitability diets and long periods of heat stress will negatively affect colony performance, and that these two effects will act interactively, with large colonies being less affected than small ones
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