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キーワード:
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要旨:
In the first attempt to re-establish a population of the red-winged grasshopper, Oedipoda germanica (Latr.), threatened with extinction in Germany, 32 adults (19 females, 13 males) were taken from a population in a limestone quarry, individually marked, and translocated to the "Leutratal" nature reserve near Jena, Thuringia, formerly inhabited by the species. A simulation model with two scenarios was run to determine the probability of re-establishment of this small translocated population. One of the two scenarios indicated that populations of 20 females could survive with optimal life history parameters. In 1994, the year of translocation, during seven nights of observation between July and September, 25 adults were re-observed at least once. About 50% of the females and 70% of the males were found in a 20 m radius of the release point, whereas a maximum distance of about 70 m was recorded for a female. Using minimum female life-span and oviposition data from greenhouse experiments, 545 eggs were estimated to have been laid by the initial inoculum in 1994. In the subsequent years 1995 and 1996, only seven and three grasshoppers were observed within 30 m of the release point in 1994. However, the translocated population obviously went extinct in 1997 because no O. germanica could be found in that or following years. By comparing source and release habitat, the possible causes of the failed re-establishment were elucidated. In the year of release a short mean adult life span of 26 days was observed, assumed to be the consequence of high predation, and resulting in a lower reproductive rate. In the following years, low soil temperature of the release habitat probably delayed egg hatching for about 1 week, delaying phenology and thereby reducing the period over which eggs could be laid. A rapid population decline resulted in only three females found in the year before extinction.
