Modelling Interaction of Genetic Problems in Small Populations and Minimum Viable Population Size

An important goal for conservation is to define minimum viable population sizes (MVPs) for long-term persistence in the face of ecological and genetic problems. Such genetic problems include mutation accumulation (MA), inbreeding depression (ID) and loss of genetic variation at loci under balancing selection, but most studies on MVPs only include ID. Verbal arguments suggest that extinction risk is exacerbated when genetic problems interact, but a comprehensive quantitative theory is missing. Using deterministic and stochastic eco-evolutionary models, we estimated MVP size as the lowest population size that avoids an eco-evolutionary extinction vortex after sufficient time for mutation-selection-drift equilibrium to establish. As mutation rates increase, MVP size decreases rapidly under balancing selection but increases rapidly under ID and MA. MVP sizes also increase rapidly with increasing number of loci with the same or different selection mechanism until a point is reached at which even arbitrarily large populations cannot survive. However, when keeping the number of loci constant, the observed MVP size is dominated by the mechanism which when in isolation yields the smallest MVP estimate. For better estimates, there is need for more empirical studies to reveal how different genetic problems interact in the genome.