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Indicator summary

 Summary of indicator structure and function

Examples of how the indicators is used for ecosystem management and ecosystem status and trends

Definition and/or background

The following is from Fulton et al (2004a) -

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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). (Figure provided by Fulton et al 2004a).

The taxonomic similarity (Δ_S) 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, Δ_S is a measure of b-diversity (turnover in species along a gradient) (Izsak and Price 2001). A taxonomic similarity matrix is constructed by calculating Δ_S 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 Δ_S 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).

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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:

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where P_i is the proportional abundance of the ith species and a and α determines the relative weighting towards species richness or dominance. The approach involves calculating H_{a α} for a range of a values and then plotting H_{a α} against a α. 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: 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). (Figure provided by Fulton et al 2004a).

Attribute

Community structure and heterogeneity

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fisheries, birds and mammals

Taxa

Data required

The following is from Fulton et al 2004a -

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Should be suitable for all ecosystems, though these indices have only been tested for benthic communities in the North Sea and fish communities in the north-east Atlantic (Rogers et al. 1999 in Jennings et al. 2001).

Identified capability

Biological classification level

Response variable

Drivers

Is there any additional information that would be of interest in regards to ecological drivers?

If not can leave this section blank and just fill in the table instead.

Robustness

The following is from Fulton et al 2004a -

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Réyni index:Medium, it may be useful for comparing community diversity, but the approach may suffer from at least some of the problems mentioned above as dogging standard diversity indices.

Current status and trends

what was it like in an undisturbed/unexploited system?

how would it be expected to change?

which way is the indicator showing a population is going in?  decreasing or increasing ??

Management strategies and/or objectives

define a standard set of management objectives?? ie from Indiseas

• Conservations biodiversity
• Ecosystem stability and resistance to perturbations
• ecosystem structure and functioning
• resource potential

has it been used in a management strategy? if so how?

relationship to management strategies/ objectives

Stakeholder/public acceptability

Acceptability with stakeholders

• by all stakeholder
• by the public
• understandable to the stakeholders

Associated links

Hyperlinks to organisations, databases, webportals, and ID books, that are associated with this indicator, if appropriate.

References

Fulton, E.A., Smith, A.D.M., Webb, H., and Slater, J. (2004a) Ecological indicators for the impacts of fishing on non-target species, communities and ecosystems: Review of potential indicators. AFMA Final Research Report, report Number R99/1546.

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Fulton, E.A., Fuller,M., Smith, A.D.M., and Punt, A. (2004) Ecological indicators of the ecosystem effects of fishing: Final report. AFMA Final Research Report, report Number R99/1546.

Possible references for updating this indicator

Citation

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