Taxonomic Ratios of Odonata (Insecta) Indicate Anthropogenic Landscape Disturbances in Subtropical Grassland Streams

ABSTRACT Streams in South American subtropical grasslands are under increasing environmental pressure. The development of biological indices to assess impacts on streams in this region is important from both conservation and applied perspectives. Metrics based on the Odonata (Insecta) community structure are useful for assessing anthropogenic disturbances in tropical forest streams. However, little is known about the potential of Odonata‐based metrics to assess impacts on streams in non‐forest landscapes. Here, we assess the potential of taxonomic ratios of Odonata as tools to assess anthropogenic disturbances in streams across the South Brazilian grasslands. We tested the relationships of ratios between the number of taxa from each suborder (“Zygoptera/Anisoptera” ratios) and between families and genera within each suborder with anthropogenic land cover surrounding each stream. “Zygoptera/Anisoptera” ratios and ratios of the damselfly genus Argia (“ Argia /Zygoptera”) were negatively related to anthropogenic land cover, while “Libellulidae/other Anisoptera” ratios were positively related. In addition, threshold analysis found that “ Argia /Zygoptera” ratios were negative indicators of anthropogenic land cover. Our study expands the potential of taxonomic ratios of Odonata as a biomonitoring tool for the integrity of subtropical non‐forest streams, such as those of the South Brazilian grasslands. Moreover, taxonomic ratios based on the richness of lotic‐specialist taxa within the suborder Zygoptera can reflect the degree of anthropogenic landscape disturbances. Our results contribute to developing biological indices to assess the environmental impacts of land‐use changes in streams in the Global South.