Riparian and in-channel habitat properties linked to dragonfly emergence

Zoë G O’Malley,Wendy A Monk,Donald J Baird,Zacchaeus G Compson,R Allen Curry,Jessica M Orlofske

doi:10.1038/s41598-020-74429-7

Abstract

In freshwater ecosystems, habitat alteration contributes directly to biodiversity loss. Dragonflies are sentinel species that are key invertebrate predators in both aquatic (as larvae) and terrestrial ecosystems (as adults). Understanding the habitat factors affecting dragonfly emergence can inform management practices to conserve habitats supporting these species and the functions they perform. Transitioning from larvae to adults, dragonflies leave behind larval exoskeletons (exuviae), which reveal information about the emergent population without the need for sacrificing living organisms. Capitalizing on Atlantic Canada’s largest freshwater wetland, the Grand Lake Meadows (GLM) and the associated Saint John/Wolastoq River (SJWR), we studied the spatial (i.e., across the mainstem, tributary, and wetland sites) and temporal (across 3 years) variation in assemblages of emergent dragonflies (Anisoptera) and assessed the relative contribution of aquatic and terrestrial factors structuring these assemblages. The GLM complex, including the lotic SJWR and its tributaries and associated lentic wetlands, provided a range of riparian and aquatic habitat variability ideal for studying dragonfly emergence patterns across a relatively homogenous climatic region. Emergent dragonfly responses were associated with spatial, but not temporal, variation. Additionally, dragonfly communities were associated with both aquatic and terrestrial factors, while diversity was primarily associated with terrestrial factors. Specific terrestrial factors associated with the emergence of the dragonfly community included canopy cover and slope, while aquatic factors included water temperature, dissolved oxygen, and baseflow. Our results indicate that management of river habitats for dragonfly conservation should incorporate riparian habitat protection while maintaining aquatic habitat and habitat quality.

Highlights

In freshwater ecosystems, habitat alteration contributes directly to biodiversity loss
Aquatic factors may influence the transition to the adult stage, including optimal water temperature, which is necessary to synchronise mass emergence for some s pecies[23]
In order to assess the associations between specific environmental variables and dragonfly responses, we developed distance-based linear models (DistLM) in PRIMER 7 48 using a step-wise procedure and Akaike Information Criterion with corrections (AICc) to find the best fitted model even with a large number of predictor variables

Summary

Introduction

Habitat alteration contributes directly to biodiversity loss. Dragonflies, which serve as important umbrella species in aquatic s ystems[1,2], maintain dynamic functional roles as both predators and prey in terrestrial and aquatic environments[3,4] They can serve as important bioindicators for water q uality[5,6,7], mercury contamination[8], ecological s tatus[9,10], and environmental change[11]. Odonates require suitable habitat to facilitate emergence, and those species exhibiting synchronous emergence require specific environmental cues[14,15] Pressures, such as intensification of land use, flow management, and sea level rise, threaten dragonflies and their habitat[16,17,18]. Aquatic factors may influence the transition to the adult stage, including optimal water temperature, which is necessary to synchronise mass emergence for some s pecies[23]

Methods

Results

Conclusion