1. The grasshopper Bryodema tuberculata requires open and dry habitats. In Central Europe, it survives only on gravel bars along braided rivers in the Northern Alps. Even there, many populations of B. tuberculata have become extinct in the last 50 years. 2. The dynamics of braided rivers are characterized by succession and floods. Catastrophic floods occur at irregular intervals. They are capable of washing away entire gravel bars and of building new, vegetation-free gravel bars. Succession eventually leads to an almost complete loss of habitat suitable for B. tuberculata on each single gravel bar. 3. Bryodema tuberculata can persist only as metapopulations, i.e. when local extinctions due to succession or flood events are compensated for by colonization of newly created gravel bars. 4. A simulation model was used to examine how the spatial and temporal dynamics of succession, flood regime and colonization determine the ability of B. tuberculata to survive in flood-plains. 5. The results show that small populations on relatively old gravel bars are important to the persistence of B. tuberculata, even though they usually only survive for a short time, due to demographic noise. 6. The effect of catastrophic floods is ambivalent: persistence is low if time intervals between floods are too short or too long. If floods are too frequent many sub-populations are extinguished at the same time and if floods are to infrequent, local populations are eliminated by succession. 7. It is concluded that most extinctions of B. tuberculata populations in the Northern Alps are due to changes in the flood regime caused by humans. 8. Many other spatially dynamic animals and plants occupy successional habitats. We suggest that the form of model outlined in this paper, based on a dynamic habitat mosaic, be used for such organisms.