Site attachment and displacement of adults in two alpine metapopulations of Somatochlora alpestris (Odonata: Corduliidae)


Site attachment and displacement of adult Somatochlora alpestris were studied by means of mark-release-resighting during two years at two clusters of ponds (A, B) ca 8 km distant from each other on opposite slopes of Prättigau Valley in the Swiss Alps. Data on 127 marked tenerals in 1998 and 92 in 2000 at (A) were obtained. Additionally, in 1998, 187 and in 2000, 23 matures were marked at (A) and 162 at (B). No marked individuals were detected during the prereproductive period in the surroundings of the breeding sites. 14.0% of the males and 7.1% of the females marked as tenerals in 1998 were resighted at water subsequently. In 2000 the corresponding resighting rate was significantly lower due to a cold spell (4.0% and 2.4%, respectively). Only one male was resighted for the first time at its emergence pond. The resighting rates of marked adults at (A) were 59.2% (males) and 28.6% (females) in 1998, but only 5.6% and 0% in 2000, respectively. The corresponding resighting rates at (B) in 2000 amounted 27.1% (males) and 9.1% (females). Site attachment and displacement during the reproductive period differed between the two study sites. At (A) site attachment was modest and limited to the largest ponds. Many individuals shuttled between neighbouring ponds and some did so between waters distant up to 2 km from each other. Individuals at (B) exhibited stronger site attachment than at (A) with many being recorded exclusively at their marking water. No marked dragonfly was found to cross the main valley. We conclude that differences in site fidelity and displacement between the localities are due to weather conditions (affecting survival probability), population density (influencing competition) and separation of ponds by forest (inhibiting commuting flights).

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