Using distance sampling to quantify Odonata density in tropical rainforests


Quantitative data are essential for many aspects of ecological research. Several methods exist to quantify odonate abundance, but complications may arise when abundances in different habitats need to be compared. In this study, I explored a technique that can overcome the variable detectability of odonates in habitats with different visibility. Distance sampling is briefly introduced and the main assumptions are listed. I conducted line transect surveys using distance sampling protocol over several weeks in a rainforest locality in Papua New Guinea to assess the usefulness of distance sampling. The results suggested that estimates of encounter rate and density of odonates are substantially higher when distance sampling is employed. Density in habitats with poor visibility, like the forest interior, is severely underestimated by traditional sampling methods, and this can lead to a misclassification of habitats. Distance sampling is a very useful technique for quantitative odonate sampling, but the sampling effort required for precise estimates is very high. For the rainforest locality in this study at least 15 months of intensive sampling would be required. Further limitations of distance sampling are discussed.

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