The role of small secondary biotopes in a highly fragmented landscape as habitat and connectivity providers for dragonflies (Insecta: Odonata)

Habitat loss and degradation are considered major threats to freshwater biodiversity and to invertebrates in particular. These often irreversible processes may lead to local and regional extinctions of species, most notably of stenotopic taxa. In spite of this, a number of studies have shown that small habitat patches can sustain rich and abundant communities. The present work assesses the relevance of a group of four small man-made (secondary) wildlife ponds to Odonata species diversity and abundance. Results obtained on pond recruiting capacity, species richness, abundance and habitat use by means of exuviae collection and monitoring of adults using a capture–mark–recapture (CMR) method indicate the potential suitability of these small aquatic biotopes and the surrounding landscape as habitat providers and stepping stone connectors in the Vallès lowlands (Catalonia, Spain). This region, close to the metropolitan area of Barcelona, has severely degraded natural habitats and high landscape fragmentation due to infrastructure, urban and industrial expansion. A comparison among a greater number of sites (ponds and sections of streams and rivers) distributed across the region showed that adequately managed small waterbodies harbour richer Odonata communities than others that are unmanaged or managed specifically for other types of fauna or uses. Appropriate care of these small biotopes avoids disturbance and keeps them free from vertebrates like fish and waterfowl which, under certain conditions, may have a strong influence on the invertebrate communities because, apart from feeding on larvae, they may have a negative impact on macrophyte development and water quality. While rivers and streams, the only natural aquatic habitats in the area, may be both expensive and technically challenging to restore and manage successfully, the creation and/or restoration of small ponds and short river sections in suitable locations can be a cost-effective method for enhancing freshwater vegetation and invertebrate diversity in this impacted landscape.