Resistance scale
Resistance indicates whether a receptor can absorb disturbance or stress without changing character (adapted from Holling, 1973; Tillin et al., 2010; Tyler-Walters et al., 2023).
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Resistance (rank) |
Description |
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None |
Key functional, key structural, characterizing species severely decline and/or physico-chemical parameters are also affected e.g., the removal of habitats causing a change in habitat type. A severe decline or reduction relates to the loss of 75% of the extent, density or abundance of the selected species or habitat component e.g., loss of 75% substratum (where this can be sensibly applied). |
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Low |
Significant mortality of key and characterizing species with some effects on physico-chemical character of habitat. A significant decline or reduction relates to the loss of 25-75% of the extent, density, or abundance of the selected species or habitat component e.g., loss of 25-75% of substratum. |
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Medium |
Some mortality of species (can be significant where these are not key structural, key functional or characterizing species) without change to habitats relates to the loss of <25% of the species or habitat component. |
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High |
No significant effects on the physico-chemical character of the habitat and no effect on the population viability of key or characterizing species but may affect feeding, respiration and reproduction rates. |
The following terms are used to explain if a resistance assessment is not possible.
‘Insufficient evidence (IEv)’– is recorded where there is not enough evidence to assess the sensitivity of the specific feature/pressure combination, there is no suitable proxy information regarding the habitat (biotope) or species on which to base decisions, and expert judgement alone does not allow an assessment to be made with any confidence. An assessment of ‘Insufficient evidence’ means that, while there may be evidence of the effect of the pressure on the specific or similar features, it is incomplete, inconsistent, or otherwise not adequate to make an assessment with any confidence.
In addition, ‘Insufficient evidence’ is recorded when the evidence allows a species or habitat to be assessed as ‘Not sensitive’ to one or more sources (or pathways) of the pressure, the evidence does not allow an assessment of known additional sources (or pathways) of the pressure. Further evidence is required to make an inclusive assessment. For example, a habitat may be ‘Not sensitive’ to one or more known invasive species but it would be misleading to conclude that it was ‘not sensitive’ to one or more invasive species where the evidence is not conclusive. Note, that if the species or habitat is assessed as ‘sensitive’ to one or more pressure sources the ‘worst-case’ scenario is presented.
‘No evidence (NEv)’ – is recorded where there is no evidence on which to base an assessment of the sensitivity of the specific feature/pressure combination, there is no suitable proxy information regarding the habitat (biotope) or species on which to base decisions, and expert judgement alone does not allow an assessment to be made with any confidence. For example, some species have a limited distribution (e.g., a few or only one location) so even basic physical, chemical, or biological tolerances cannot be inferred.
Not relevant (NR) – is recorded where the evidence base suggests that there is no direct interaction between the pressure and the biotope group. 'Not relevant’ is also used to denote interactions that are unlikely to occur at present or in future and to denote interactions that are literally ‘not relevant’, for example, deep mud habitats are not exposed to changes in emersion. In addition, ‘Not relevant’ is used to denote ‘default’ assessments that result from the definition of the pressure.
Not assessed (NA) – is recorded where the available evidence is extremely limited, poorly understood, or completely absent, and no assessment is attempted. For example, the likely effects of the pressure ‘Marine litter’ (pre-2014) on marine species were poorly understood and little studied so it was not possible to set a sensible ‘benchmark’. ‘Not assessed’ was also recorded for the ‘pollutant’ pressures because it was felt that the 2014 pressure benchmark (compliance with all relevant environmental standards) could be misleading.
