Taxonomic Distinctness as a Measure of Diversity of Stream Insects Exposed to Varying Salinity Levels in South-Eastern Australia

John Wiley & Sons, Ltd
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River Conservation and Management, 2012, 1, pp. 175 - 182
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Average taxonomic distinctness (delta+) is a measure of the mean taxonomic breadth of a sample and is thus a measure of biodiversity. It has the great advantage of not being sensitive to variations in sampling effort, unlike measures of species richness, and is thus potentially of great value for examining the effects of disturbance on biodiversity. In addition, it is possible to test delta+ for departures from expectation. The increasing level of salinity in rivers in Victoria and South Australia is a well known environmental hazard. Delta+ was calculated using all insect species or the subset of Ephemeroptera, Plecoptera and Trichoptera (EPT) species from the bank and main channel habitats at 941 and 607 sites respectively. Samples from these sites were classified into 16 salinity categories (ranging from 0.05 to 30 mS cm-1). Delta+ values for the insects showed minor change and were close to the expected value until salinity levels reached 7-14.9 mS cm-1; at higher salinities delta+ declined and became significantly different from expectation. When EPT species were used trends were less consistent and the decline at higher salinities was weaker. Feeding group diversity within each salinity category declined more or less linearly as delta+ decreased.
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