Refugees from lost habitat and reorganization of genetic population structure

When habitat is lost, individuals of many species are able to flee and rees tablish themselves in other sites, such cases may be studied with refugee m odels of genetic population structure, The fleeing refugees carry their gen es, which can result in a reorganization of genetic structure. Differentiat ion among demes (F-ST) is reduced, and additive genetic variance (V-A) with in remaining demes is increased. These effects accumulate for as many gener ations as habitat continues to be lost. After habitat loss and stabilizatio n of a new habitat structure, generic differentiation among demes and fixat ion of rare or deleterious alleles will again increase by genetic drift, a slow process, and will ultimately, equilibrate at nero levels of F-ST and V -A. The temporary increase of V-A in surviving demes increases their mean f itness and can forestall problems with inbreeding depression and the abilit y of demes to adapt to environmental changes It is likely that a large prop ortion of species of conservation concern are able to flee during habitat l oss, Many of these have probably recently experienced significant genetic r estructuring and have not returned to equilibrium levels of genetic differe ntiation. This introduces a temporary upward bins when interdemic gene flow rates (Nm) are inferred from F-ST, and it inflates the measures of the lon g-term standing genetic variance, V-A, that those populations are able to m aintain. In principle, these biases can be estimated and some guess aspects of prefragmentation genetic structure can be recovered, but much more empi rical data are needed on the dynamics of refugee establishment.