Changing distribution patterns along a stream in adults of Calopteryx haemorrhoidalis (Odonata: Calopterygidae): a case of larval-drift compensation?


The distribution of an isolated population of adult Calopteryx haemorrhoidalis was studied along a small stream in NE Spain, during two-week or three-week summer periods over five years. Distribution patterns differed consistently between age groups. Reproductive activities took place along the entire stream, whereas the presence of tenerals and older immature individuals was restricted to the lower reaches of the stream. It is concluded that emergence took place only in the lower reaches and that this can be explained by larval drift due to strong currents regularly depleting the upper half of the stream.

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