Nectar collected with microcapillary tubes is less concentrated than total nectar in flowers with small nectar volumes
Previous research indicated that microcapillary tubes greatly underestimated sugar present in flowers with low nectar volumes, but it was unclear whether tubes missed liquid nectar or whether sugar concentration in nectar they collected did not represent total sugar concentration in a flower. We determined the suitability of microcapillary tubes to estimate the energetic value of Acrotriche patula R.Br. (Ericaceae) nectar from total sugar mass. We collected a standing crop of nectar from individual flowers with microcapillary tubes and subsequently washed the flowers to recover putatively any residual sucrose, glucose, and fructose. We assessed microcapillary nectar volume as a predictor for total sugar mass in a flower by regression analysis, identified the percentage of sugar missed by microcapillary tubes, and compared sugar ratios between microcapillary samples and total nectar. Nectar volume collected with microcapillary tubes cannot be used to predict total nectar sugar contents in a flower. Microcapillary tubes missed 71% of the floral sugar on average, but not a large volume, indicating that sugar is not evenly distributed in a flower’s nectar. Proportions of different sugars did not differ significantly between microcapillary samples and total samples. Animals with different tongue morphologies and feeding behaviours may obtain different energetic rewards from the same flower with low nectar volume. Variation in a flower’s nectar at one point in time is likely to favour the generalisation of pollination systems.