A practical tool for evaluating freshwater health and biodiversity across Africa

[摘要] ENGLISH ABSTRACT: The diverse African freshwater ecosystems are being increasingly impacted by human activities.Biomonitoring tools are needed to address the level of impacts and success of mitigation. Here abiomonitoring tool, using an effective indicator group (Dragonflies: Odonata), is developed at theAfrican continental scale, while using the South African Dragonfly Biotic Index (DBI) as a startingpoint. The DBI can be applied to both still and running waters, and is based on three sub-indices(geographical distribution, threat status, and habitat sensitivity) of each dragonfly species. Data ondragonflies has been collated through international effort into the Odonata Database of Africa, usedhere to develop a new index, the African Dragonfly Biotic Index (ADBI). As with the DBI, the ADBIuses the same first two sub-indices (distribution and threat status), but replaces habitat sensitivity witha species vulnerability sub-index. This is more appropriate for the continental level in view of thequality of data available. Careful data interrogation led to final selection of 604 African dragonflyspecies for development of the ADBI. While the South African DBI scores were calculated at anational level, the ADBI scores were determined at a continental scale, which necessitated somechanges in the calculations of the ADBI scores. To determine exactly how the ADBI deviated fromthe DBI, these two biotic indices were compared using just the South African dragonfly species as adata sub-set. There was a strong correlation between the Red List threat status sub-index and finalscores of the ADBI and DBI, while geographical distribution sub-index scores of the ADBI and DBIwere only moderately correlated. The sub-index that contributed most to the deviation of the ADBIfrom the DBI, was the ADBI species vulnerability sub-index. Although appropriate for a continentalscale assessment, the ADBI has shortcomings for national level assessments, where conservationpolicy and management takes place. This meant that the ADBI had to be translated for specific usein the different countries so as to develop national biomonitoring schemes (i.e. a national DBI).However, as the spatial database created for Africa's dragonflies varies in quality and quantity, thecountries are at various levels of national DBI development. Countries were categorized on theirpotential to develop national DBIs by determining the value of data coverage of each country. Of the48 African countries (excluding South Africa, which already has a national DBI), there are 12 thatare close to being able to implement national DBIs, while another 12 have insufficient data and arenot currently able to implement national DBIs. The other 24 countries require much more basic datato instigate national DBIs. Bioassessments of freshwaters takes place at two levels: 1) within politicalborders, and 2) in biogeographical regions. However, what is expedient at the national level oftendoes not match biogeographical categories (e.g. ecoregions). Hence, the continental-scale ADBI wasinvestigated according to Africa's terrestrial and freshwater ecoregions. There were no significantdifferences between assessments using terrestrial vs. freshwater ecoregions, although using terrestrialecoregions gives a finer interpretation of freshwater condition.

[发布机构] Stellenbosch University