Dynamic modes of population size and its genetic structure for species with nonoverlapping generations and stage development

Abstract

This study investigates a simple model of stage-structured population with density-dependent birth rate. We assume that the breeding season of a population occurs at a certain time of the year, its individuals undergo two stages during their life cycle, and the adjacent generations are nonoverlapping. Reproductive isolation between generations is caused by mature individual death after breeding and leads to the fact that increasing intraspecific competition results in subcritical period-doubling bifurcation in the proposed model. Periodic, quasiperiodic, and chaotic oscillations appear in the model, as well as shifting of the dynamic regime due to multistability. Furthermore, we propose that the maximum possible fecundity of individuals changes during natural evolution and is an adaptive trait controlled by a single diallelic autosomal locus with allelomorphs A and a. As a result, the population consists of three genotypes, namely, аа, АА, and Аа, with different values of reproductive potential. This study shows that the genetic composition of a population (i.e., whether the population will be polymorphic or monomorphic) is mainly determined by the values of the reproductive potentials of heterozygotes and homozygotes. The average reproductive potential of mature individuals and the intensity of self-regulation processes determine the population dynamic mode. The evolutionary development of a population can occur in three ways depending on the current genetic composition at the same values of demographic parameters. The first way gives a monomorphic population with genotype aa. The second one leads to genotype AA monomorphism. And the last way results in polymorphism which presents 2-cycle of genotype's frequencies. The microevolution scenarios of the population's genetic composition found in the proposed model are associated with fluctuations in numbers and are consistent with studies on Pacific pink salmon populations which demonstrate population size fluctuations and genetic differentiation of subpopulations of adjacent generations.