Abstract
We collected environmental and habitat data for nymphs of 12 dragonfly species (Odonata: Anisoptera) from 91 stream sites throughout eastern Texas, including urban and non-urban locations. Understanding the relationship of dragonflies to habitat structure and other environmental variables is crucial for the purpose of conserving these insects and better using them as predictive tools for water quality assessments, and refining tolerance values. The objectives of this study were to determine the key environmental variables influencing the diversity and distribution of dragonflies in eastern Texas streams, and further determine if differences in those factors could be observed between urban and nonurban sites. We collected samples separately from benthic habitats and woody snag habitats. Significantly fewer sites were observed to have dragonfly species on snag habitat (mean = 1.25) compared to benthic samples (mean = 14.67) (t-test, p = 0.001). The number of dragonfly species collected among non-urban streams (mean = 9.83) was not significantly different than urban streams (mean = 6.08; t-test, p = 0.07). Detrended correspondence analysis of benthic and snag habitat data collected from non-urban and urban locations showed that most of the species are oriented most closely to benthic habitats in non-urban streams. Snag habitat was shown to be poorly ordinated for all of the species. A canonical correspondence analysis of 29 water quality and habitat variables as environmental determinants of dragonfly diversity and distribution showed that distributional relationships among species are complex and often described by multiple environmental factors.
Highlights
Dragonflies (Odonata: Anisoptera) are a relatively large, diverse group that exhibits a broad range of reactions to environmental stressors, making them useful indicators of water quality [1,2,3,4,5,6,7,8,9,10]
This paper summarizes the results of dragonfly nymphs collected from streams located in three eastern Texas ecoregions in relation to water quality, habitat, and environmental stressors with particular attention to urban versus non-urban streams
The most important finding of this study was that the number of dragonfly species occurring in urbanized streams was not significantly different than that of non-urban streams, non-urban streams collectively had a numerically greater representation of total species
Summary
Dragonflies (Odonata: Anisoptera) are a relatively large, diverse group that exhibits a broad range of reactions to environmental stressors, making them useful indicators of water quality [1,2,3,4,5,6,7,8,9,10]. Development and use of regionally focused tools for assessing aquatic condition is important for the state of Texas where there is a vast diversity of aquatic ecosystems [11,12]. To develop such assessment tools, it is imperative to understand the environmental and habitat drivers that dictate the distributions of the targeted species. Nymphs potentially can be influenced by a broad array of environmental variables both biotic and abiotic [13], emphasizing a need to better understand such influences.
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