Metapopulation viability: influence of migration

We investigate the effects of migration pattern on the reduction in metapopulation fitness due to deleterious mutations. Using a matrix approach and stochastic simulations we explore the case of a metapopulation consisting of two and three populations. Both in the long and in the short-term, the viability of a two-populations system depends strongly on the symmetry of exchange, i.e. metapopulation viability is maximized when the number of migrants sent equals the number of migrants received in each population. For a three-population system, the same principle holds in the few cases explored, but a complete demonstration is still needed. In other terms, a very unfavorable situation occurs when a population that receives few migrants is a major source of migrants for the other populations. In conclusion, low but symmetrical number of migrants leads to higher viability than higher but asymmetrical number of migrants. Assuming that it is easier to decrease than to increase the number of migrants, a reasonable management option in the case of unequal number of migrants, could, therefore, be to decrease the higher ones.