Odonata community structure in artificial habitats

Several factors act on community structure determining species composition and abundance patterns. Core processes act at local scale (communitylevel) shaping the observed assemblages like: species’ abiotic requirements and species interactions (competition, predation). Artificial habitats (for their simplified structure) are useful models for assessing the main factors affecting community composition and a good proxy to disentangle the assembly rules of the species that inhabit such habitats. Drinking troughs (brickwork tanks) are widespread in Italy and represent a suitable aquatic habitat to be colonized by various taxa. Dragonflies are usually found in drinking troughs and provide an interesting model to study such patterns of assemblage structure. We searched for Odonata communities exhibiting non-random co-occurrence/segregation patterns in drinking troughs in central Italy. We collected 13 Odonata species larvae from 37 sites, built presence/absence matrices, and performed null-model analyses by measuring C-score (co-occurrence index). Libellula depressa was the commonest species (21 presences), followed by Sympetrum sanguineum (17 presences). We found a pattern of non-random structure for the communities. Interspecific interactions may be the major force driving to observed segregation pattern between species. Focusing on larval-stage, the presence of structured assemblages can be expected due to simplified habitat characterizing drinking troughs that should facilitate larval population growth close to the threshold at which density-dependent interspecific interaction are likely to occur, generating pattern in the very short-term (one year/one season). Interactions within sprawlers (ecological-guild) could be the main driver for the observed total structure, in particular the direct effect of intraguild predation between Crocothemis erythraea and Sympetrum spp., that showed high C-scores values in the couple co-occurrence analysis. Overall, intraguild-predation among larvae at different development stages may result in effective segregation pattern, representing a primary process to take into consideration when studying Odonata assembly rules and predict the evolution of the communities in these artificial habitats.