Odonata Assemblages in Urban Semi-Natural Wetlands

Abstract

As the human population in urban areas is continuously growing, urbanization is one of the greatest threats to biodiversity. To mitigate the negative effects, the inclusion of blue zones (aquatic habitats) in modern urban development practices is strongly recommended, as they could be beneficial for the local biodiversity conservation. Odonata are a flagship group and are widely used in freshwater conservation as ecological indicators of habitat integrity and health. However, our understanding of their ecological requirements in urban landscapes is not yet complete. Therefore, we analyzed the taxonomic and functional diversity of Odonata in a semi-natural wetland in the Croatian capital. This study was conducted in the summers of 2020 and 2023. Most taxonomic and functional assemblage metrics were comparable between the two main habitat types, anthropogenically disturbed and natural oxbow lakes. However, significant differences were found in relation to the time scale, where most metrics were lower in 2023, indicating the negative impact of extreme climate events (including droughts) that occurred in this region after 2020. With 19 species recorded, our results indicate that semi-natural urban wetlands, especially natural oxbow lakes, have great potential to function as good habitats for Odonata, where even some species of conservation concern were detected. When developing landscape management plans in urban areas, it is essential to consider the importance of habitat heterogeneity in terms of good structure of aquatic macrophytes (presence of submerged, emergent and floating vegetation), which would ensure the most suitable habitat conditions for local Odonata species.

Keywords: damselflies; dragonflies; large rivers; life history traits; man-made habitats; oxbow lakes.

Figure 1

Geographical depiction of the Savica significant landscape in the city of Zagreb, Croatia, featuring photographic examples of the study sites. Legend: light grey spots—anthropogenically disturbed lakes, dark grey spots—natural oxbow lakes.

Figure 2

Cluster analysis of study sites belonging to anthropogenically disturbed and natural oxbow lakes in the Savica urban lakescape in the city of Zagreb, Croatia, based on the composition of Odonata assemblages. Legend: H—Hawaii, ZG—Žuta graba, VJ—Veliko jezero, V—Vrbova, U—Ušće lakes. Numbers 1–3 are sampling events.

Figure 3

Odonata taxonomic assemblage metrics at anthropogenically disturbed and natural oxbow lakes in the Savica urban lakescape in the city of Zagreb, Croatia: (a) species richness, (b) abundance, (c) Shannon diversity index, (d) Simpson diversity index. Asterisks indicate significant differences in metrics between the different years of the study (* = p < 0.05).

Figure 4

Dragonfly Biotic Index (DBI) calculated for anthropogenically disturbed and natural oxbow lakes in the Savica urban lakescape in the city of Zagreb, Croatia.

Figure 5

Functional diversity (RaoQ index) of Odonata assemblages at anthropogenically disturbed and natural oxbow lakes in the Savica urban lakescape in the city of Zagreb, Croatia, presented as mean and standard deviation (SD).

Figure 6

Functional traits of Odonata at anthropogenically disturbed and natural oxbow lakes in the Savica urban lakescape in the city of Zagreb, Croatia, presented as mean and standard deviation (SD) in relation to: (a) body shape, (b) habitat preference of species for lateral connectivity, (c) current preference of species, (d) species dispersal capacity, (e) reproduction type. Asterisks indicates a significant difference between the habitat types and between the different years of the study (*** = p < 0.001, ** = p < 0.01, * = p < 0.05). Legend: yr—year; CWM—community weighted mean; EUP—eupotamon, PARA—parapotamon, PLE—pleisiopotamon, PAL—palaeopotamon, TWB—temporary waterbodies; LIMN—limnophilous, LIM-RHE—limno- to rheophilous, RHE-LIM—rheo- to limnophilous, RHE—rheophilous; ETS—eggs laid attached to substrate, EIS—eggs laid into the substrate, SUB—eggs laid not attached to or in substrate, OWA—eggs laid in open water, IPL—eggs laid inside plant tissue, OPL—eggs laid onto plant material, ORS—eggs laid on exposed soil or rock.