Michael J. Samways and John P. Simaika: Manual of freshwater assessment for South Africa: Dragonfly Biotic Index
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Odonata (dragonflies and damselflies) are the paramount insect flagship group for quality assessments of freshwater bodies. Their value in conservation is enhanced as the adults are tractable and attractive diurnal insects in which interest can easily be encouraged, and that value has been increased massively with the production of ever-more complete and well-illustrated and user-friendly handbooks to identify species within regional faunas. Thus, the handbook to South African species by Michael Samways (2008) established an effective template for further study of that fauna, and the present document is a valuable extension of that work to increase the appreciation and values of dragonflies in monitoring freshwater quality. It is also an attractive full-colour production, user-friendly and easy to understand by people who perhaps have little familiarity with dragonflies. In reviewing this book, I must declare my long friendship with Michael Samways. We have collaborated on several projects (some leading to co-authorships) over some 30 years of mutual interests in insect conservation.
Development of the ‘Dragonfly Biotic Index’ within the context of the entire South African fauna, and in a form that it can be used as a credible practical tool for managers of the country’s freshwater ecosystems, is a notable achievement. Its authority is undoubted—more than 70 relevant papers by the senior author and his colleagues dominate the reference listing of this book, and further commentary by the authors (Samways and Simaika 2017) adds to the perspective.
The Index draws on three main themes, which are combined to produce a wider evaluation of each of the 162 species present: the general distribution of the species, the threat status from IUCN Red-Listing categories, and its sensitivity to environmental changes. Each component is allocated, by clearly explained divisions, on a ‘0–3’ numerical scale, so that the final index value for a species ranges from ‘0’ (a common, widespread, unthreatened and disturbance–tolerant species) to ‘9’ (a highly restricted, threatened and sensitive species). Only nine species gain this highest rating level but a further 37 species gain levels above zero in all three assessment categories, and only 10 species remain at overall ‘0’. Adding the individual species scores for all the taxa in an assemblage gives a wider collective measure of that assemblage. Because the Index is founded objectively at the species level, the authors claim it is ‘robust, versatile and sensitive’. The book also displays the extension of using the Index to contribute to a wider ‘Habitat Condition Scale’, as a guide to the state of stream habitats, as discussed in an earlier contribution (Simaika and Samways 2012).
Background is provided on dragonfly survey procedures—with the many practical points discussed having considerable value in planning surveys elsewhere: indeed, that very practical section deserves careful attention by anyone planning dragonfly surveys. Species recognition is clear—the bulk of the book is a page-by-page summary of each species, with a distribution map, and the colour photographs of living individuals of each species a notable feature. Many photographs are annotated with the key diagnostic features of the species, and the authors note that many species can be identified through binoculars and without need to capture them. Line diagrams of genitalic features are also provided where needed for clear diagnosis. Each page also prominently displays the species’ threat status and index score; this key information is summarised also in the introductory section, in which tables include a synthesis of the incidence of species across the country’s 31 ecoregions, and a summary of their national and global Red List categories with the detailed breakdown of each of the Dragonfly Biotic Index subdivisions. More generally, that Introduction includes much information useful in considering dragonflies in ecological evaluations and as a perspective of the South African fauna. An up-to-date checklist of species, including current and older vernacular names, is also a useful reference tool.
The book is a thoughtful contribution to the use of insects in conservation assessments, and also emphasises the relevance of Red List assessments of individual species in the wider context of assemblages. Displayed through this comprehensive regional account, the approach can be applied at variety of different scales. This Manual deserves wide attention, and is a fine practical example for emulation elsewhere.