MODELING PERSISTENCE IN DYNAMIC LANDSCAPES - LESSONS FROM A METAPOPULATION OF THE GRASSHOPPER BRYODEMA-TUBERCULATA

1. The grasshopper Bryodema tuberculata requires open and dry habitats . In Central Europe, it survives only on gravel bars along braided riv ers in the Northern Alps. Even there, many populations of B. tubercula ta have became extinct in the last 50 years. 2. The dynamics of braide d rivers are characterized by succession and floods. Catastrophic floo ds occur at irregular intervals. They are capable of washing away enti re gravel bars and of building new, vegetation-free gravel bars. Succe ssion 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 t o succession or flood events are compensated for by colonization of ne wly created gravel bars. 4. A simulation model was used to examine how the spatial and temporal dynamics of succession, flood regime and col onization determine the ability of B. tuberculata to survive in flood- plains. 5. The results show that small populations on relatively old g ravel bars are important to the persistence of B. tuberculata, even th ough they usually only survive for a short time, due to demographic no ise. 6. The effect of catastrophic floods is ambivalent: persistence i s low if time intervals between floods are too short or too long. If f loods are too frequent many subpopulations are extinguished at the sam e time and if hoods are to infrequent, local populations are eliminate d by succession. 7. It is concluded that most extinctions of B. tuberc ulata 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 fo r such organisms.