Many plants produce pollen, such as conifer species, wheat and corn. Those pollens are generally produced with little, if any, nectar produced by the same plants. They are also much lower in nutritional value to the bees, than many other pollens, but when other pollens are less abundant, the bees will collect and eat them. Likewise, other plants, which produce more nutritious pollens, do not always produce copious nectar, too. Though, generally, when I see some pollen, of assorted colors, being brought in, I usually expect enough nectar is available for colonies to avoid starvation.