Predicted fitness changes along an environmental gradient

The relations between enzyme activity and the intensity of selection across an environmental gradient are investigated using Escherichia coli growing on mixed resources. Experimental results demonstrate that the direction and intensity of natural selection can be predicted solely from a knowledge of the underlying biochemistry, physiology and ecology of the organism. Ecological theory, based on the logistic equation, is unable to use this information to predict the outcome of competition - the best it can do is to fit constants to data points. Our results also suggest that partitioning of the phenotypic variance using quantitative genetics need not correspond to the underlying molecular structure generating phenotypes.