Temporal variation of an Odonata species assemblage (Rome, Italy)

The Castel Porziano estate is a well preserved coastal Mediterranean woodland, rich in still bodies of water, where odonatological studies have been taking place since the '50s. Adult Odon. were recorded for the entire estate in 1997 and 1998 (March-Nov.; 2 checks each month). 1,838 adults (22 spp.) were marked, to assess their movements. The results showed that in 1997-1998 a total of 31 spp. were present. This number is very close to the number (29) recorded up to 1976. Variation in species assemblage in 16 ponds was observed from 1997 to 1998. Although the overall species similarity was preserved, the number of spp. for each pond and the number of ponds inhabited by each sp. significantly increased from 1997 to 1998. In regard to the adult movements, 251 marked individuals of 13 spp. were re-sighted only at the same ponds where they had been marked and 30 individuals of 6 spp. were sighted at different ponds. Among the latter, the majority moved within a range of a few hundred metres, but some individuals were able to fly quite far, e.g. 2.7 km (Coenagrion puella) and 5.8 km (Libellula depressa). It is concluded that the assemblage variation for the entire estate was small, varying more on a decennial than on an annual scale, but for a single pond variation is wider on both time scales. The quick recolonization among ponds, due to the adult's movements, appears to be the cause of greater stability at mesoscale rather than at local scale.