Dragonflies are Hemimetabola insects, which spend the longest period of their life spans as larvae in the aquatic phase. Wetland habitats and vegetation are important for the whole life history of dragonflies. This paper demonstrates the relationship between wetland vegetation and the ecological distribution of dragonflies in the Beijing area. It also comments on the conservation of dragonflies and their habitats.
Field studies were carried out between May 2001 and August 2004 to study the diversity of dragonflies in the area. A total of 36 species of Odonata were reported, belonging to 26 genera and six families. The characteristics and diversity of wetland vegetation were also studied by sampling 296 quadrats at 17 randomly selected plots representing different wetland types in Beijing including rivers, reservoirs, lakes and montane streams. Information was collected regarding dragonfly species and encounter rate and also composition of aquatic plants, coverage of floating-leaved aquatic plants, phreatophytes, sub-emergent aquatic plants and emergent aquatic plants. The G-F index and Gleason richness index were used to assess the diversity of wetland plants.
By employing the Two-way Indicator Species Analysis (TWINSPAN) and Canonical Correspondence Analysis (CCA), the 17 plots were divided into four groups, each of which supported different dragonflies and may and thus shed light on habitat preferences. CCA ordination demonstrated that the richness of aquatic plants and the integrality of wetlands vegetation communities played the most significant roles. It suggested aquatic plants may supply habitat for dragonflies in their foraging, emergence, copulation and oviposition. Results of an assessment of key ecological factors of wetland vegetation show that coverage of floating-leaved aquatic plants is the most important single factor affecting the distribution of Odonata species. Other factors are coverage of phreatophytes (Gleason richness index), coverage of sub-emergent aquatic plants (G-F index), and coverage of emergent aquatic plants.
Wetland vegetation, richness of aquatic plants and integrality of wetlands vegetation communities have profound effects on the ecological distribution of dragonflies in the Beijing area. However, the construction of urban wetlands involves the clearing of aquatic plants and the introduction of exotic plants into water bodies. Therefore, the integrality of wetlands vegetation should be preserved and managed.