Temporal trends and effects of vegetation cover on functional and taxonomic diversity in Odonata assemblages of a protected area in northern Italy

Odonata is a charismatic taxon that has key ecological roles in both aquatic and terrestrial habitats. Recently, a functional approach, which is based on the concept of “trait”, has received an increasing attention in community ecology because it allows to link biodiversity, ecosystem functioning and conservation targets. In this study, we investigated temporal trends of functional and taxonomic facets of diversity in Odonata assemblages inhabiting ponds within the Regional Park of Montevecchia and Valle del Curone (northern Italy), where a standardised monitoring program has been performed through five years between 2012 and 2019. Moreover, we investigated how functional and taxonomic diversity metrics are linked to vegetation characteristics (relative cover of types of vegetation) at site level. We found stable temporal trends for functional richness, dispersion, evenness, species richness and Shannon’s diversity, while a weak decrease of taxonomic evenness was found. Contribution to functional richness was found to increase as function of the first axis in the functional space (i.e. larger species and fliers). Concerning the effects of vegetation on community diversity, functional richness and dispersion were positively influenced by increasing covers in horsetail (Equisetum) and submerged aquatic vegetation, whilst negatively influenced by cattail cover (Tipha). Sedge cover (Carex) showed a positive effect on functional evenness; riparian shrub vegetation and common reed (Phragmites australis) positively influenced Shannon’s diversity. Overall, these findings suggest that in the study area the assemblages have remained quite stable in terms of both functional and taxonomic diversity, also pointing out how types of vegetation can affect diversity at community level.