A practical tool for evaluating freshwater health and biodiversity across Africa

Vorster, Carlien (2018-12)

Thesis (PhD)--Stellenbosch University, 2018.

Thesis

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 a biomonitoring tool, using an effective indicator group (Dragonflies: Odonata), is developed at the African continental scale, while using the South African Dragonfly Biotic Index (DBI) as a starting point. 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 on dragonflies has been collated through international effort into the Odonata Database of Africa, used here to develop a new index, the African Dragonfly Biotic Index (ADBI). As with the DBI, the ADBI uses the same first two sub-indices (distribution and threat status), but replaces habitat sensitivity with a species vulnerability sub-index. This is more appropriate for the continental level in view of the quality of data available. Careful data interrogation led to final selection of 604 African dragonfly species for development of the ADBI. While the South African DBI scores were calculated at a national level, the ADBI scores were determined at a continental scale, which necessitated some changes in the calculations of the ADBI scores. To determine exactly how the ADBI deviated from the DBI, these two biotic indices were compared using just the South African dragonfly species as a data sub-set. There was a strong correlation between the Red List threat status sub-index and final scores of the ADBI and DBI, while geographical distribution sub-index scores of the ADBI and DBI were only moderately correlated. The sub-index that contributed most to the deviation of the ADBI from the DBI, was the ADBI species vulnerability sub-index. Although appropriate for a continental scale assessment, the ADBI has shortcomings for national level assessments, where conservation policy and management takes place. This meant that the ADBI had to be translated for specific use in 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, the countries are at various levels of national DBI development. Countries were categorized on their potential to develop national DBIs by determining the value of data coverage of each country. Of the 48 African countries (excluding South Africa, which already has a national DBI), there are 12 that are close to being able to implement national DBIs, while another 12 have insufficient data and are not currently able to implement national DBIs. The other 24 countries require much more basic data to instigate national DBIs. Bioassessments of freshwaters takes place at two levels: 1) within political borders, and 2) in biogeographical regions. However, what is expedient at the national level often does not match biogeographical categories (e.g. ecoregions). Hence, the continental-scale ADBI was investigated according to Africa’s terrestrial and freshwater ecoregions. There were no significant differences between assessments using terrestrial vs. freshwater ecoregions, although using terrestrial ecoregions gives a finer interpretation of freshwater condition.

AFRIKAANSE OPSOMMING: Die diverse varswater ekosisteme van Afrika word toenemend deur menslike aktiwiteite belemmer. Bio-moniterings instrumente word benodig om die vlak van impakte en sukses van mitigering te monitor. ʼn Bio-moniterings instrument word hier ontwikkel, vir ʼn Afrika kontinentale-skaal, deur gebruik te maak van ʼn effektiewe aanwysers groep (Naaldekokers: Odonata) en die Suid-Afrikaanse Naaldekoker Biotiese Indeks (NBI) as ʼn begin punt. Die NBI word toegepas vir beide stilstaande en lopende water, en is gebaseer op drie sub-indekse (geografiese verspreiding, bedreigings status, en habitat sensitiwiteit) van elke naaldekoker spesie. Inligting oor naaldekokers was deur internasionale ywer in die Odonata Databasis van Afrika (ODA) saamgestel en word hier gebruik om ʼn nuwe indeks, die Afrikaan Naaldekoker Biotiese Indeks (ANBI), te ontwikkel. Soos met die NBI, gebruik die ANBI dieselfde twee sub-indekse (verspreiding en bedreigings status), maar vervang habitat sensitiwiteit met ʼn spesies kwesbaarheid sub-indeks. Dit is meer gepas vir die kontinentale vlak nemende die kwaliteit van beskikbare inligting. Omsigtige ondersoek van hierdie inligting, het gelei tot die ontwikkeling van die ANBI vir ʼn finale seleksie van 604 Afrikaanse naaldekoker spesies. Terwyl die Suid-Afrikaanse NBI punte op ʼn nasionale vlak bereken word, was die ANBI punte op ʼn kontinentale vlak bepaal, wat sekere verandering in die berekeninge van die ANBI punte vereis het. Om te bepaal presies hoe die ANBI vanaf die NBI afwyk, was hierdie twee biotiese indekse met mekaar vergelyk deur net Suid-Afrikaanse naaldekokers as ʼn data-ondergroep te gebruik. Daar was ʼn sterk korrelasie tussen die Rooilys bedreigings status sub-indeks en finale punte van die ANBI en NBI, terwyl die geografiese verspreiding sub-index punte van die ANBI en NBI slegs matig gekorreleerd was. Die sub-indeks wat die meeste tot die afwyking van die ANBI vanaf die NBI bygedra het, was die ANBI spesies kwesbaarheid sub-index. Alhoewel geskik vir ʼn kontinentale-skaal waardebepaling, het die ANBI tekortkominge vir nasionale vlak waardebepaling, waar bewarings-beleid en bestuur plaasvind. Dit beteken dat die ANBI verander moet word om nasionale bio-moniterings skemas (d.w.s. nasionale NBI) te ontwikkel vir spesifieke gebruik in die verskillende lande. Nietemin, deurdat die ruimtelike databasis, wat vir Afrika se naaldekokers opgestel was, verskil in kwaliteit en kwantiteit, is die lande by verkeie vlakke van nasionale NBI ontwikkeling. Die lande was gekategoriseer volgens hul potentiaal om nasionale NBIs to ontwikkel, deur die waarde van elke land se inligting te ondersoek. Van die 48 lande (uitsluitend Suid-Afrika, wat alreeds ʼn nasionale NBI het), is daar 12 wat naby daaraan is om nasionale NBIs te implementeer, terwyl nog 12 lande onvoldoende inligting het en op die oomblik nie in staat is om nasionale NBIs te implementeer nie. Die ander 24 lande vereis baie meer basiese inligting om nasionale NBIs in werking te stel. Bio-waardebepalings van varswater vind plaas op twee vlakke: 1) binne politiese grense, en 2) in biogeografiese streke. Nietemin, wat aangewese is op ʼn nasionale vlak, gaan dikwels nie saam met biogeografiese kategorieë nie (bv. omgewings-streke). Dus, was die kontinentale-skaal ANBI volgens Afrika se land en varswater omgewings-streke ondersoek. Daar was geen betekenisvolle verskille gevind tussen die waardebepalings van land vs. varswater omgewings-streke nie, alhoewel die gebruik van land omgewings-streke ʼn nouer interpretasie van die varswater-toestand gee.

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