Ecological thresholds of Odonata larvae to anthropogenic disturbances in neotropical savanna headwater streams

We evaluated whether ecological thresholds could be detected along gradients of disturbances by using larval Odonata genera. Morphological, physiological, and behavioral differences between Odonata suborders may be reflected in different thresholds to anthropogenic disturbance. Therefore, we hypothesized that larval Zygoptera genera would have narrower ecological thresholds in response to increased levels of stream disturbance and would be considered sensitive to anthropogenic disturbances, and the opposite for larval Anisoptera genera, which would have wider ecological thresholds and would be considered tolerant to anthropogenic disturbances. We assessed 30 larval Odonata genera collected from 186 headwater stream sites in the Neotropical Savanna. Threshold Indicator Taxa Analysis detected ecological thresholds in seven Odonata genera (Argia, Brechmorhoga, Cacoides, Gomphoides, Phyllocycla, Progomphus and Hetaerina) revealing them as robust bioindicators (purity and reliability & GE; 0.85). Most Zygoptera were associated with less-disturbed sites and most Anisoptera were associated with more-disturbed sites, but not all genera corresponded to this pattern. Therefore, we recommend using Odonata larvae at the genus-level, versus the suborder level, for constructing improved biomonitoring tools and obtaining more accurate impact assessments of neotropical stream sites.