Great Basin Naturalist


We compared nectar production in wild populations and greenhouse-grown populations of the monkey flower species of section Erythranthe of the genus Mimulus. Nectar was sampled from over 1000 flowers. For each flower the volume of nectar was measured with a calibrated micropipette and the percentage of sugar with a hand refractometer. Percentage of sugar varied little from flower to flower in both field and greenhouse studies, but volume varied markedly from flower to flower in field studies and even more in greenhouse studies. This high variance in nectar volumes appears to be intrinsic. The amount of nectar in greenhouse populations tended to increase with time in the absence of pollinators. The amount of nectar in field populations tended to remain the same to pollinator withdrawals. The latter conclusion was corroborated by sampling nectar at 2-h intervals all day and comparing the total volume produced by a flower to the volume of nectar produced in control flowers sampled only at the end of the day.