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The nutritional significance of a winter‐flowering succulent for opportunistic avian nectarivores
Author(s) -
SYMES CRAIG T.,
MCKECHNIE ANDREW E.,
NICOLSON SUSAN W.,
WOODBORNE STEPHAN M.
Publication year - 2011
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1111/j.1474-919x.2010.01072.x
Subject(s) - nectar , crassulacean acid metabolism , biology , δ13c , isotope analysis , botany , ecology , zoology , photosynthesis , stable isotope ratio , physics , quantum mechanics , pollen
The winter‐flowering succulent Aloe marlothii provides nectar for many opportunistic avian nectarivores in southern African savannas. We assessed the importance of A. marlothii nectar sugar for opportunistic nectarivores by analysing temporal changes in stable carbon isotope ratios (δ 13 C) in the tissues of birds in Suikerbosrand Nature Reserve, South Africa. The blood of the 11 most common non‐granivorous opportunistic nectarivores at our site was enriched in 13 C by 3.4 ± 1.5‰ during the flowering period of A. marlothii , reflecting the enriched crassulacean acid metabolism (CAM) isotopic signature of nectar (−12.6 ± 0.5‰). This relatively small contribution of A. marlothii nectar to assimilated carbon in whole blood contrasted with that of exhaled CO 2 in African Red‐eyed Bulbuls Pycnonotus nigricans and Cape White‐eyes Zosterops capensis . In both these species, the δ 13 C of breath samples was significantly enriched compared with blood and feathers, and closely resembled that of the nectar, revealing combustion of ingested nectar rather than assimilation. Although our analysis was complicated by the presence of C 4 grasses, whose δ 13 C values are similar to those of CAM photosynthesizers, when considered with previously published feeding observations our data reveal that opportunistic nectarivores feeding on A. marlothii nectar obtain a relatively small fraction of their assimilated carbon, but most of their metabolized carbon, from this seasonally available carbohydrate food resource. Because the δ 13 C values of insects associated with C 3 plants also became enriched during the flowering season, some insect‐eating opportunistic nectarivores may have assimilated A. marlothii carbon indirectly from insects. This study highlights the importance of understanding isotopic routing when assessing the nutritional significance of specific dietary items to consumer communities.