Untersuchungen zum Überleben der Heuschrecken (Caelifera et Ensifera) in der Überschwemmungsaue der Elbe bei Dessau (Sachsen-Anhalt)

Abstract

Fischer, N.; Witsack, W.: Studies on the survival of the grasshoppers (Caelifera et Ensifera) in theflooded meadows of the Elbe near Dessau (Saxony-Anhalt). – Hercynia N.F. 42 (2009): 255 – 304.The populations of grasshoppers were investigated in flooded meadows of „Biosphärenreservat Mittelelbe“in 2005 and 2006. The focus of the study was on differences in the composition of speciesdue to flooding conditions, furthermore, the possibilities of survival for each stage of development andthe different seasons were reviewed. On plots of four flood-affected areas, two meadows with no floodand seven plots in a transect through the meadows 6500 grasshoppers in 22 species were found. It wasshown, that there are high similarities between flood-plains und non-flood-plains. The abundance anddominance of each species was more connected to the type of meadow (wide open meadows or meadowssurrounded by forests). Even the dry and wet subunits show marginal differences in the dominance-identity.Thermophilic grasshoppers, as Chorthippus biguttulus, were present on non-flooded areas and thedryer parts of the flooded meadows. Hygrophile species, such as Stethophyma grossum or Conocephalusdorsalis, were detected in the moist parts of the flood-plains. For most grasshoppers the only possibilityto survive a flood is in the egg phase. The species of the flood plots successfully survived the springfloods in 2005 and 2006 in the egg stage. In summer floods the larvae and most imagines drown. But stilloccurring eggs of the preceding year can ensure the survival of the species at this time. This is shown bythe young hatched larvae in late June and July. Females of the new generation with eggs appear in Julyin years without flood. The eggs of these females can save the population from summer floods (frommiddle of July to beginning of August) to the next year. The overlapping of the egg-generation ensuresthat the grasshopper populations can survive in this way floods during all times of summer. Macroptergrasshoppers are also able to escape a flood by flying. The grasshopper Chorthippus parallelus isbrachypter,but also occurs in macropter morphs. As such it was detected on the investigated meadows,but just in low numbers and randomly distributed. However, macropter animals could repopulate areasafter a flood. Investigations after the Elbe floods in the spring of 2005 and 2006 and in August 2002 suggestthat the stage for maintaining the population is mostly the egg stage.Key words: Caelifera, Ensifera, ecology, phenology, survival on flood, flooded meadows, Elbe meadows,Saxony-Anhalt.