The near convergence of evolutionary and ecological time
It has been proposed that ecological and evolutionary time may ‘converge’ because rates of evolution are often fast enough that trait changes can be detected in the same time scales in which ecological processes unfold. Because changes in allele frequencies require the turnover of individuals, however, a convergence of ecological and evolutionary time implies that rates of evolutionary change and rates of change in population size should also be very close. This possibility has not been broadly assessed. We derived a model to show how the rates of change in a trait should depend on the rate of change in population size, through the effects of fitness gradients and heritable trait variation. We then compiled data on rates of population and trait change from the literature, for studies where both were measured at the same time. We used these data to examine how the rate of change in traits compares to the rate of change in population size.
Our results indicate that rates of change in phenotypes are generally no more than ⅔ and on average about ¼ the concurrent rates of change in population size. This result holds for a wide range of species and taxonomic groups. We also found that the variance of both phenotypic and ecological rates increased with the mean following a power law with an exponent of two, while temporal variation in phenotypic rates was lower than in ecological rates. Together, our results suggest that only rarely do populations change as fast in traits as they do in abundance. Our study helps to forge a quantitative link between ecology and evolution and provide context for understanding eco-evolutionary dynamics.