Measuring investment in carnivory: seasonal and individual variation in trap number and biomass in Utricularia vulgaris L.

Abstract

The partitioning of biomass between traps and leaves is a measure of the investment in carnivory of Utricularia vulgaris and is dependent on the relative values of three attributes: trap size, trap number and leaf size. Marked seasonal and individual variations in trap size, trap number and leaf size occur within a small population of U. vulgaris at Wicken Fen, Cambridgeshire, UK, with some plants consistently having fewer traps per leaf than others, and some smaller leaves than others, throughout the growing season. However, the three attributes vary independently, so that all combinations over the observed ranges of trap size, trap number and leaf size occur simultaneously in the population. In spite of the variation in the three constituent factors, the proportion of biomass invested in traps is close to 50% in the majority of plants and throughout most of the growing season. The contribution of traps to total biomass cannot be predicted from the number of traps per leaf. Although the proportion of biomass represented by traps is the most useful measure of a plant's investment in carnivory, the precise way in which the biomass is partitioned between a variable number of traps of different sizes may also be an important consideration in cost-benefit analyses.