A five year survey of an odonate community inhabiting a North Venezuelan mountain stream

Monthly counts of adult odon. were carried out along a transect following a forested mountain stream, «Quebrada Pasaquire». 17 of the 41 spp. recorded were considered for evaluation. The average monthly abundance curve of spp. such as Euthore fasciata Sel., Archilestes grandis (Ramb.), Philogenia cassandra Sel., Progomphus abbreviatus Belle, Brechmorhoga rapax Calv. and Libellula herculea Karsch matches the climogram of the study area, e. g. these spp. are markedly seasonal, with high adult abundances in the wet season, and low numbers in the dry season. On the other hand the presence of adult Hetaerina capitalis Sel. and H. cruentata (Ramb.) did not seem to be correlated with season Macrothemis pseudimitans Calv. and Micrathyria venezuelae De Marmels appeared to be more common in the dryer months, but their population sizes were always low. Based upon the data of this survey it can be stated that the odon. community studied has a persistent structure, relatively low variabilities of population densities, and is stable. The evidence includes persistence of the dominant taxa over at least 5 generations, typical standard deviations of the logarithm of population sizes, as well as high and significant year-to-year rank concordance. Cannaphila vibex (Hag.) and Progomphus abbreviatus became more common during this survey, while Andaeschna rufipes (Ris) shifted towards local extinction. However, 5 yr may not be sufficient to show such trends to be irreversible: in almost all species at least one trend reversal occurred during the survey. Some of the potential ecological mechanisms underlying the constancy and stability of this odonate community are discussed and it is suggested that abiotic factors, such as periodical floods in this lotic habitat, may be of some concern.