Emergence patterns of riverine dragonflies (Odonata: Gomphidae) in Hungary: variations between habitats and years

Abstract

In this paper the results of a six-year study on riverine dragonflies (Odonata: Gomphidae) emergence based on the systematic collection of exuviae are presented. The exuviae were counted to determine variations in species composition, abundance and emergence pattern of gomphids at four different sites along the rivers Tisza and Szamos, as well as at a selected site in five different years. While the number of species decreased, the abundance of exuviae increased downstream the river Tisza. The total numbers of exuviae differed significantly between the dammed and non-dammed sites. The emergence of gomphids varied in initiation, synchronisation and also in duration between sites as well as between years. The onset of emergence was dependent mainly on the species-specific temperature sums, consequently earlier or later emergence resulted from the differences in the spring water temperature. The duration of emergence in G. flavipes and G. vulgatissimus was twice as long at the dammed site, characterised by a higher larval density, as at the other sites. In the degree of synchrony G. flavipes showed the emergence characteristics both of the spring and the summer species. Such interyear variations at the same site might have been attributed to the differences in annual fluctuations in the water temperature, indicating that rising temperatures may influence not only the onset of emergence but the synchrony as well.

Keywords:

• Tisza and Szamos rivers
• exuviae; onset of emergence
• synchronisation
• effects of temperature

Acknowledgements

We wish to thank the Upper-Tisza Environmental and Water Directorate, especially Gáspár Bodnár, Károly Uray and the Tóth family, for providing the facilities for our studies; the Environmental and Water Management Directorate of the Tiszántúl Region for access to water temperature data; Balázs I. Mátyus for placing his data on exuviae at our disposal. We are also very grateful to the referees Manuel Ferreras-Romero and Frank Suhling for his helpful comments and suggestions on the manuscript.