When sources become sinks: Migrational meltdown in heterogeneous habitats

We consider the evolution of ecological specialization in a landscape with two discrete habitat types connected by migration, for example, a plant-ins ect system with two plant hosts. Using a quantitative genetic approach, we study the joint evolution of a quantitative character determining performan ce in each habitat together with the changes in the population density. We find that specialization on a single habitat evolves with intermediate migr ation rates. whereas a generalist species evolves with both very low and ve ry large rates of movement between habitats, There is a threshold at which a small increase in the connectivity of the two habitats will result in dra matic decrease in the total population size and the nearly complete loss of use of one of the two habitats through a process of "migrational meltdown. " In some situations. equilibria corresponding to a specialist and a genera list species are simultaneously stable. Analysis of our model also shows ca ses of hysteresis in which small transient changes in the landscape structu re or accidental demographic disturbances have irreversible effects on the evolution of specialization.