explicit models were designed to let dispersal probability be a function of patch size or the distance between local habitat patches [@Hanski94; @Hanski02]. One aspect of dispersal that only has been implicitly included in realistic models but not studied in isolation is when dispersal is asymmetric. Asymmetric dispersal is expected for many metapopulations, e.g. where dispersal is dominated by wind transport of pollen and seeds [@Nathan01], and for marine species with spores and larvae transported by ocean currents [@Wares01]. Consequently, it is important to understand how asymmetric dispersal may affect the dynamics and persistence of metapopulations with potential implications for the design of nature reserves. Some studies have considered asymmetric dispersal [e.g. @Pulliam91; @Kawecki02; @Artzy-Randrup10] but have not analysed effects on metapopulation viability.

In a recent contribution a conceptual model was developed to explore the effects of dispersal asymmetry on metapopulation persistence [@Vuilleumier06]. The viability of metapopulations was investigated for different dispersal patterns randomly connecting pairs of patches through either unidirectional or bidirectional dispersal routes. @Vuilleumier06 concluded, that asymmetric dispersal leads to a distinct increase in the extinction risk of metapopulations. In a similar study @Bode08 investigated correlations between metapopulation viability and statistics of the dispersal network; they also found 