Corolla depth and nectar concentration: an experimental study

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Abstract
The effect of corolla depth on nectar concentration was examined both by field surveys of nine different species and by experimental manipulation of the spurs of flowers of Aquilegia caerulea. The surveys showed that the relationship between concentration and corolla depth was influenced by present and past environmental conditions. The Aquilegia caerulea experiment demonstrated, as expected, that nectar evaporates much faster in flowers with small effective corolla depths than in those with deep corollas. These results affect the usefulness of arguments about the adaptive significance of nectar concentrations. Here it is suggested that the dilute nectars reported from hummingbird flowers are a secondary consequence of their having evolved deep tubular flowers.