ESTIMATING BIRD FITNESS CORRECTLY BY USING DEMOGRAPHIC-MODELS

One aim of studies in evolutionary biology is to estimate the fitness of a phenotype within a population. One of the most natural estimates of fitness is lambda, the multiplication rate, or finit rate of increase, which results from the demographic parameters of that particular phenotype. Even though ad hoc computations of lambda may be strongly biased, they are still widely used, in particular in bird population biology. We compare ad hoc computation of the multiplication rate and exact ones using demographic models. The magnitude of the discrepancy increases sharply with the departure of lambda from unity. This may alter our perception of population functioning. Other outputs of demographic models, which play prominent roles in bird evolutionary biology and population management, are briefly discussed. As a whole, demographic models provide a link between empirical and theoretical approaches.