Comparative nectar-foraging behaviors and efficiencies of an alien and a native bumble bee |
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Authors: | Marcelo A Aizen Mariana Lozada and Carolina L Morales |
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Institution: | (1) Laboratorio Ecotono-CRUB, Universidad Nacional del Comahue and INIBIOMA, Quintral 1250, 8400 San Carlos de Bariloche, R?o Negro, Argentina |
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Abstract: | Resource preemption by alien organisms can contribute to their invasion success and the demise of functionally equivalent
native species, particularly when opportunistic foraging by aliens results in more efficient exploitation. In forests of NW
Patagonia, the only native bumble bee and major pollinator, Bombus dahlbomii, declined almost to extinction as the alien B. ruderatus increased in abundance since its first appearance about 17 years ago. To explore whether resource competition might have
driven this displacement we studied the behavior and foraging efficiency of both bumble bees while they harvested nectar from
flowers of Alstroemeria aurea, the main summer food resource in the forests of NW Patagonia. We compared the nectar content of flowers that bees selected,
recently visited, and rejected with that of randomly-chosen neighboring flowers and assessed differences in visitation rates.
The native bumble bee selects flowers with abundant nectar and mostly exploits nectar-rich flower patches by rejecting a higher
proportion of flowers with little or no nectar. On the other hand, the alien bumble bee discriminated less with respect to
sugar content per visited flower, but visited more flowers per minute. Workers of the native bumble bee harvested ~70% more
sugar per unit of time than those of the alien species in absolute terms, and a similar amount when sugar harvested was expressed
as a percentage of body mass. In contrast to expectation, the opportunistic foraging of the alien bumblebee was not more efficient
and therefore cannot explain the ecological extinction of the native species through exploitative competition. These findings
suggest that the displacement of the native species by the alien may be driven by other factors, such as the associated introduction
of novel diseases or parasites. |
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