De trage terugkeer van libellen naar tijdelijk opdrogende duinplassen

BEUKEMA, J.J. & R. MANGER, 2007. The slow return of dragonflies to dune ponds that temporarily dry up. Brachytron 10(2): 212- 218. Numbers of Odonata were counted twicemonthly for four years along the banks of two nearby (0.5 km) shallow artificial ponds in the dunes of the north-western part of The Netherlands. The shallowest pond dried up completely in late-summer of 2003. In the subsequent year, numbers of Odonata were abnormally low at this pond. Moreover, the first individuals arrived much later in the season as compared to other years and to the other (permanent) pond. This was so in all five common species. The earlyspring species Ischnura elegans and Enallagma cyathigerum were belated by two months, the other species (Lestes sponsa. L. barbarus, Sympetrum spec.) by two to four weeks. These results are in accordance with reports on other studies, which indicate that exchange between populations of nearby ponds goes generally slowly and involves only low proportions of such populations.