Classification Features

2.1 Background on the African Dragonfly Biotic Index (ADBI)

The African Dragonfly Biotic Index (ADBI) is similar in principle to the South African DBI, i.e. to rapidly assess the changing conditions of freshwater ecosystems in Africa. As with the DBI, the ADBI is based on the presence of adult odonates (Anisoptera and Zygoptera) within the continent’s freshwater ecosystems. It, like the DBI, consists of three sub-indices, but each is slightly different to accommodate the differences in spatial scale, i.e. national for the DBI and continental for the ADBI.

The three sub-indices of the ADBI are: 1) a species’ geographical distribution, 2) its IUCN/SSC Red List threat status, and 3) its vulnerability to negative anthropogenic disturbances to its habitat. Any of the selected African dragonfly species’ can have any one sub-index score ranging from 0 to 3, and as each species is assigned three sub-index scores, a species’ ADBI can range from 0 to 9, i.e. 0 + 0 + 0 to 3 + 3 + 3.

As the three indices of the ADBI are determined at a continental scale, while the DBI sub-indices are national, the three sub-sub-indices of the ADBI were calculated differently from those of the DBI. This means that: 1) the scoring for the species’ IUCN/SSC Red List threat status was determined exclusively at a global scale (i.e. with no national status), 2) the geographical distribution was determined at the continental scale (African continent), and 3) the species vulnerability to

anthropogenic disturbances to their habitats were also assessed at a continental scale, i.e. measuring the adverse anthropogenic impacts to the species preferred habitats and their possible reactions (African continent).

The difference between the ADBI and the DBI sub-index ‘geographical distribution’, is that this DBI sub-index is based on conservation-action units, i.e. the political boundaries of state provinces. This geographical distribution sub-index is ideal for South Africa as the provinces also happen to be biogeographically meaningful (Samways & Simaika 2016). However, this is not necessarily the case for the rest of the African continent. This meant that an alternative geographical approach had to be adopted for the African continent that was both practical and yet useful for the development of a meaningful ADBI geographical distribution sub-index at the continental level.

Subsequently, the ADBI geographical distribution sub-index was calculated using the Odonata Database of Africa (ODA), which is a comprehensive spatial database of individually recorded dragonfly species across the African continent (Kipping et al. 2009; Dijkstra et al. 2011; Clausnitzer et al. 2012; Simaika et al. 2013). The geographical coordinates located within this database were used to determine the latitude-longitude range sizes of the respective species across the African continent.

The range sizes were divided into four categories that are represented by the sub-scores 0 to 3 (see Chapter 2).

In the case of the DBI sub-index ‘Red List threat status’, both the national and global statuses were used, whereas for the whole continent, there are no national Red List threat statuses, only global ones. For each species, the ADBI (global) Red List threat status sub-index was the same as that on IUCN/SSC Red List threat status, as established by the IUCN Red List Categories and Criteria, version 3.1, second edition (IUCN 2016). These threat statuses were also divided into four categories that are represented by the sub-scores 0 to 3 (see Chapter 2). The Red List threat status for each African dragonfly species were obtained from the website www.iucnredlist.org.

The DBI sub-index ‘habitat sensitivity’ was based on the level of occurrence of dragonflies in fully natural versus human-modified or created habitats. This could be done for South Africa, as the species in the country are relatively well known, which is not so when the odonate assemblage is scaled up to a continental level. In contrast, the ADBI species vulnerability sub-index was determined using a habitat matrix, the African Dragonfly Habitat Matrix (ADHM), which was created by 15 dragonfly specialists who described the preference of each dragonfly species for a particular habitat.

This sub-index was calculated by first determining how sensitive the habitats may be to the impacts specific anthropogenic disturbances may have on them (i.e. habitat conversion, water management and the presence of alien trees) and second, how vulnerable each species may be to these impacts within their particular habitats. This species vulnerability sub-index was also divided into four

categories that are represented by the sub-scores 0 to 3 (see Chapter 2). Descriptions of these three ADBI sub-indices with their respective sub-scores are given in Table 3.1.

2.2 Data

The data covers the 162 South African dragonfly species in Samways and Simaika (2016). In turn, the data here includes the three sub-index scores and final scores of both the DBI and the ADBI. The three sub-index and final scores of the South African DBI were taken from Samways and Simaika (2016), while the three sub-index and final ADBI scores are from Chapter 2. Although the data are sourced from a similar dataset, two different groups of biotic values are compared with each other so as to identify whether the ADBI measures up to the original DBI. All 162 species, with their corresponding three sub-index scores and final scores of both the DBI and ADBI, are listed in Appendix B1.

2.3 Data analyses

To determine the extent of correlation between the ADBI and the DBI, the data (categorical) were examined as follows. Firstly, a non-parametric Kolmogorov-Smirnov (K-S) one-sample test for normality was used to determine whether or not the data, as described above, had a normal distribution. Secondly, a non-parametric Spearman Rank Correlation (-0.7 ≤ r ≤ 0.7) was used to determine whether any significant relationships existed between the three sub-indices, as well as between the final scores of the DBI and ADBI. Next, to assess how the scoring of 162 South African dragonfly species might have changed, the species’ three sub-index scores and final scores of the DBI were visually compared with the respective species’ three sub-index scores and final scores of the ADBI. Finally, the veracity of the third sub-index of the ADBI (species vulnerability) was re-examined by recalculating the final ADBI scores of all the South African species. This was accomplished by using the DBI third sub-index (habitat sensitivity) scores instead of those of the ADBI third sub-index (species vulnerability). Thus, the original DBI scores were compared with the new ADBI scores of the 162 species, which includes ADBI sub-indices 1 (geographical distribution) and two (threat status) plus the DBI sub-index 3 (habitat sensitivity). All data were interrogated using STATISTICA 13 (Dell Inc. 2016).

Table 3.1. Description of the three sub-indices of both the South African Dragonfly Biotic Index (DBI) and the African Dragonfly Biotic Index (ADBI).

The three sub-indices are: geographical distribution (DBI and ADBI sub-index 1), threat status (DBI and ADBI sub-index 2), habitat sensitivity (DBI sub-index 3) and species vulnerability (ADBI sub-index 3). The IUCN/SSC threat status abbreviations (IUCN 2016) are: DD – Data Deficient, LC – Least Concern, NT – Near Threatened, VU – Vulnerable, EN – Endangered, CR – Critically Endangered, GS – Global Status, NS – National Status. For the South African DBI, the highest threat status (NS and/or GS) was used. Other abbreviations: lat-long – latitude-longitude.

Scores South African Dragonfly Biotic Index African Dragonfly Biotic Index

Distribution Threat Sensitivity Geographical Distribution Threat Status Species Vulnerability 0 Very common throughout South

1 Localised across a wide area in South Africa, and localised or