Unpredictable community composition of adult dragonflies (Odonata: Anisoptera) in a pond metacommunity

Background/Question/Methods

Membership in communities is determined by both biotic and abiotic processes, across local and regional scales. Animals with high dispersal capabilities, such as dragonflies (Odonata: Anisoptera), may be subject to additional filters in this assembly process due to habitat selection behavior. The presence of the larvae of each dragonfly species in a pond community is heavily dependent on the presence or absence of fish; however, adults may not have the ability to directly identify the suitability of a pond for their offspring. To overcome this, adults may use secondary cues to assess potential predation pressure before ovipositing. In addition, newly emerged adults, having survived the larval stage, could also exhibit differing dispersal behaviors to optimize fitness, such as either philopatric or indiscriminate dispersal. In order to gauge the amount of discriminate habitat selection exhibited by adult dragonflies, a metacommunity of ponds in north Texas was censused for larval and adult dragonfly densities and abundances, respectively. The environmental characteristics of each pond, particularly the presence or absence of fish, was recorded, as well as the spatial location of each pond. Variance decomposition was used to analyze the role of environmental characteristics and spatial location in determining the composition of species in each pond.

 

Results/Conclusions

Environmental and spatial factors did not significantly explain the composition of adult dragonfly communities. Larval dragonfly communities were significantly explained by environmental characteristics only. Adult dragonfly communities therefore appear to be indiscriminate regarding their selection of ponds in which to oviposit, whereas larval compositions are determined through heavy species sorting. This contrast indicates that adults may hedge their bets against significant environmental change; in this environment, that likely includes drought, which significantly affects the presence or absence of fish. Adult dragonfly metacommunities are therefore supported by source-sink patch dynamics, with the locations of sources and sinks changing with each drought event.