...
| Indicator | Attribute | Purpose | If restricted to taxa, list which ones | Ecosystem applicability | Identified capability | Biological classification level | Response variable | Drivers | Robustness |
|---|---|---|---|---|---|---|---|---|---|
| Diversity Diversity and taxonomic relatedness of spcies | community Community structure; heterogeneity | fisheriesFisheries | Should be suitable for all ecosystems, | D or AAspirational | Ecosystem; Community | speciesSpecies-based | anthropogenicAnthropogenic | low Low to medium |
Examples of how the indicators is used for ecosystem management and ecosystem status and trends
...
To address the issue of relatedness between species, additional measures of diversity were recently introduced by Warwick and Clarke (1995) and Izsak and Price (2001). The indices proposed by Warwick and Clarke (1995) measure taxonomic diversity (Δ), computed from species abundance data, and taxonomic distinctness (Δ*), calculated using presence-absence data or percentage cover. These are indices of taxonomic ‘relatedness’ as they consider taxonomic separation with (Δ) and without (Δ*) the contribution of species diversity. The biological basis for these indicators is that, generally, unperturbed communities have higher taxonomic separation of species, which is lost when a system is perturbed (there may be no change in simple species diversity, but the species present are now more closely related to each other) and the former system state is considered to be more diverse (Jennings et al. 2001). The indices are a measure of the taxonomic distance, or mean path along a taxonomic hierarchy between two randomly chosen individuals, though Δ* is conditional on the individuals being from different species (Jennings et al. 2001). As the path length between individuals is based on taxonomy and not genetic distance it is not true relatedness, but collecting genetic information for all species in a community is impracticable (Warwick and Clarke 1995). When this index was tested, by analysing the response of a small benthic community to pollution around an oilfield, a continuous decrease in taxonomic distinctness was detected along a gradient of increasing contamination, whereas traditional diversity indices did not detect the changes (Figure 5.1) as they are sensitive only to species diversity not the relatedness of the species and therefore cannot detect the shift in taxonomic separation mentioned above. It was also applied in an examination of the fishing effects on a North Sea fish assemblage (Hall and Greenstreet 1998), but results were less clear, even showing a slight correlation with traditional diversity indices. Nevertheless, it is believed that this indicator has potential as it is more robust (given usual data constraints and problems) than traditional diversity indices (Clarke and Warwick 1999), though more testing on fisheries data sets is required. As Δ and Δ* are average measures they are relatively insensitive to disparities in sampling effort and taxonomic rigour (Izsak and Price 2001).
Figure 5.1: Plots comparing the sensitivity of macrobenthic communities to different diversity indices along a pollution gradient around the Ekofisk oil field in the North Sea. Taxonomic distinctness and diversity increase with (log) distance from the centre of oil drilling activity, whereas similar plots for the Shannon species diversity index (H’), species richness (Margalef’s D) and evenness (Pielou’s J) show little change (after Warwick and Clarke 1995)need to add figure 5.1
The taxonomic similarity (ΔS) uses presence-absence data and is derived from the average taxonomic relatedness of any two species from different sites. It is related to Δ*, but whereas that index measures α- (within habitat) and γ- (within region) diversity, ΔS is a measure of b-diversity (turnover in species along a gradient) (Izsak and Price 2001). A taxonomic similarity matrix is constructed by calculating ΔS values for each pairwise combination of species at two sites, using the taxonomic distance and the number of taxonomic levels (species, genus, family etc) used to classify the species of interest. β-diversity is then the median (or average) value of this matrix. Preliminary studies performed during the development of ΔS indicate that it does capture β-diversity while being more robust to sampling effort and taxonomic rigour than the commonly used Jaccard coefficient (Izsak and Price 2001).
...
The Réyni index is a diversity index used in diversity ordering procedures to rank communities in terms of their diversity. The index has been used in studies of fishing effects on diversity in the North Sea (Figure 5.2) and is calculated using:
...
where Pi is the proportional abundance of the ith species and a determines the relative weighting towards species richness or dominance. The approach involves calculating Ha for a range of a values and then plotting Ha against a. If the trajectories for communities cross they are not comparable, but if one consistently falls below another (as demonstrated in Figure 5.2, which compares the diversity of fish communities in the North Sea) the community with the lower curve is considered to be less diverse (Jennings et al. 2001).
figure 5.2 needs to be added
Figure 5.2: Réyni diversity profiles for fish communities in three regions of the North Sea. The southwestern sector is more diverse, because the profiles do not cross and the profile for the southwestern area is always highest (after Rogers et al. 1999 in Jennings et al. 2001).
Attribute
Community structure and heterogeneity
...