Subpopulation & ESU delineation framework
Subpopulation and ESU delineation framework for species assessments
Purpose:
This two-phase framework is indented to help IUCN based species assessments (i.e. IUCN Red List and IUCN Green Status of Species). Species assessments are currently done at three levels: the species as a whole, different sub-species, and subpopulations. Most assessments are done however on the species level (~ 5% of species assessed have listed subpopulations). Below-species level assessment in form of a broader implementation and standardization of subpopulation listings, as well as the inclusion of Evolutionarily Significant Units (ESUs) would reflect genetic diversity patterns more accurately and aid its protection.
For more information please look at the scientific paper accompanying this framework.
The framework:
The delineation for subpopulations and ESUs is based on using both genetic and non-genetic evidence. This framework has two steps: first, identifying genetically meaningful subpopulations and, second, grouping these into ESUs(Figure 1).
To offer a clear threshold for the presence of each subpopulation or ESU, each evidence category (genetic, recorded biological and inferred) is given a score corresponding to the support they offer and the strength of their relationship with evolutionary genetic processes.
Testing:
Species should be divided into the most likely groups of subpopulations and ESUs, each grouping is called a candidate ‘scenario’.
Different scenarios can be tested for Phase 1 and 2 and subpopulations can be grouped into a smaller number of ESUs.
We recommend to base the candidate scenarios on existing knowledge and literature.
The results of the scenario with the highest score (note this may be different for subpopulations and ESUs) should be used for listing assessments.
Figure 1 – Lines of evidence (A) and the Two-phase framework (B) to assess the strength of evidence for subpopulations and Evolutionarily Significant Units (ESUs). Different lines of evidence are highlighted in color (dark green, green and blue). Maximum scores are the numbers provided below each category in the boxes based on genetic or non-genetic evidence from the literature and other documentation. Below each phase the scoring system is explained by exemplary imaginary ‘scenarios’.
Scoring:
In Phase 1 only scenarios with 2 points or higher indicate the presence of distinct subpopulations. Each scenario with ≥ 2 points can then be further investigated in Phase 2.
In Phase 2 scenarios comprising potential ESUs can be assessed (number of subpopulations and ESUs might differ). To delineate distinct ESUs, we suggest the need of some genetic/genomic evidence. Only scenarios scoring 10 points or higher are considered to contain distinct ESUs.
Scoring <10 points can have several reasons, such as compelling evidence indicating no distinctiveness, or data-deficiency in some evidence categories. With a score lower than 10 we have two options:
a) The candidate scenario could not reach or exceed 10 points (even if all missing data were supportive of the tested scenario) = no support for the ESU – Scenario.
b) The candidate scenario does not currently reach or exceed 10 points, but could do so, if missing data subsequently prove to be supportive of the tested scenario = scenario indicates possible ESUs (pESUs).
*However, if a candidate scenario currently only scores in recorded biological evidence-types (so non-genetic evidence), the scenario should be regarded as ‘data-deficient’ rather than as a pESU scenario.