Evolution of migration processes in Cladocera populations

Abstract

An intrinsic rate of population increase (r) in a local habitat is determined by the birth-to-death ratio and by migration processes. In natural populations, including Cladocera, r is estimated as the logarithm difference of population densities at the end and at the beginning of time interval. Under this method of evaluation, migration processes are already included in the final population density. A realized intrinsic rate of population increase (rmax) can be determined from the data on age-related mortality and fecundity by the life table method. The high regression relation (R2 = 0.867) was found between rmax, the first time of reproduction (Drepr) and mean fecundity during the reproduction period (mean_mx). Drepr is known for most of Cladocera, the mean_mx analog can be easily determined in their natural populations; these parameters can be used to evaluate a possible intrinsic rate of population increase (rcalc). The differences between r and rcalc can be used to evaluate migration processes. If these differences are positive, then individuals are emigrating from the population, if they are negative, then there occurs the influx of immigrants.