Environmental drivers of life stage specific distributional patterns in Odonata: Implications for biomonitoring

Background/Question/Methods

Organisms with complex life cycles exhibit dramatic ontogenetic niche shifts. These allow the same organisms to exploit different habitats and interact with different communities. Among the aquatic insects, larvae of some groups are aquatic and invest their energy mainly for growth, while adults inhabit the aquatic-terrestrial interface, investing their energy for reproduction and dispersal. In this way, different life-history stages could differentially be affected by environmental variables. Our first goal were to understand how similar or different environmental factors affect larval and adult life stages in Odonata. Second, we assessed if the distributional patterns of between (larvae and adult) and within (adult genera and species) life-history stages were congruent. We sampled larvae and adults in 44 streams distributed along a riverine network in southwest Brazil. Larvae were collected using 20 kick sampling subsamples of 1m length each; adults were collected for one hour at each site with a hand net along a 100-m transect parallel to the stream/river banks. The influence of environmental factors on larvae and adult were assessed by redundancy analysis coupled with forward selection. The congruence level between responses matrices were determined by Procrustes analysis. 

Results/Conclusions

Our results revealed that some environmental factors affect both, between (larvae and adult) and within (adult genera and species) life-history stages, helping us to understand their congruence level. Larvae and adult were 54% congruent, regardless of taxonomic level of adults and abundance of adult genera and species were 93% congruent. The effects of environmental variables on larvae and adults of odonates could be explained by how they influence each stage individually or via carry-over effects. The influence of aquatic variables, here dissolved oxygen, temperature and conductivity on larvae are related to development and survivorship, while forest cover is intrinsically related to habitat availability. Both adult genera and species were affected by dissolved oxygen and stream/river width, which could be related to oviposition behavior. Carry-over effects, i.e., larval environmental conditions that could affect adult fitness components or vice-versa are also important for explaining our results as well as females selection of more appropriate habitats for laying their eggs, which could determine larvae distribution. The practical implications for the work mainly relate to biomonitoring, our results suggest that adult genera could be used in biomonitoring programs since they capture, respectively, 93% and 54% of the information carried by adult species and larvae.