Relationships between the presence of odonate species andenvironmental characteristics in lowland ponds of central Italy

Abstract

A set of 21 ponds was sampled three times for odonate larvae during spring 2002. At the same time 17 environmental variableswere recorded including area, wet phase duration, total nitrogen, total phosphorus, aquatic macrophytes and land use. Atotalof 16 odonate species belonging to Lestidae, Coenagrionidae, Aeshnidae and Libellulidae were recorded, and the total numberof species per pond varied from zero to six. The relationships between species richness, assemblages and environmental variableswere studied by simple and multiple correlation and by Canonical Correspondence Analysis (CCA). The results showed thatpermanent ponds were larger, deeper, had more macrophyte species, had more extensive macrophytes cover and lower concentrationsof nitrogen and phosphorus than temporary ponds. Multiple regression analysis showed that the number of odonate specieswas positively affected firstly by the number of macrophyte species, and then by pond depth. However, pond depth appearedto be interchangeable with several others variables, such as pond area and water duration and negatively correlated withnitrogen concentration, variables which are all linked with the permanent or temporary status of the ponds. CCA analysis indicatedthat odonate species presence was linked with a few environmental variables, showing a tendency of Odonata to avoidponds with higher nitrogen concentrations, with the exception of Lestes barbarus, a species typical of temporary water in centralItaly. At the same time, the majority of species were linked with longer water phase duration and with greater macrophytespecies richness. Acomparison with previous studies, and in particular with those carried out in central Italy, confirmed the positiveinfluence of macrophytes, water duration, and also the negative effect of nutrient load. However, several other variables,in particular land use, shade, presence of fish, which were influential in other studies, were not significant in this study.