Application of IUCN Red List Categories on a Regional Scale by Ulf Gärdenfors

Introduction

The new IUCN Red List Categories (IUCN 1994) were developed primarily for application on the global scale, i.e. for judging the extinction risk of the whole species (or other taxon). Most countries concerned with compiling Red Lists will probably adopt the new categories in one form or another. However, by doing so, some problems may arise when the population of a species within a country (or other considered region) is only a part of a larger population. Furthermore, because the categories only consider extinction risks, there may also be other criteria that, from a national perspective, should be considered in order to develop conservation priorities.

Thus, there is a need to develop guidelines for applying the new categories at national or other regional levels in order to achieve a standardized application. To cope with the issue, IUCN has organized workshops, so far in Gland, Switzerland (March 1995; IUCN 1995) and in Cambridge, England (December 1995; Gärdenfors 1996). The process will continue, resulting in general recommendations from IUCN.

In this paper I will identify some of the conceptual problems that may arise when applying the IUCN Red List categories on a subglobal scale.

Problems at Regional Level

The IUCN (1994) categories of threat are defined by one of five criteria (A-E; see the section entitled The New IUCN Categories and Criteria in this book). The quantitative thresholds of the criteria were set roughly to correspond to each other in reflecting the extinction risk of taxa. When applying these criteria on a national or other kind of regional level, there are few problems, so long as the population of the species to be assessed is isolated from other conspecific populations, or is endemic. The extinction risk for an isolated population is the same irrespective of whether it constitutes the only population of the species in the world, or if there are other totally isolated conspecific populations. But, if the target population constitutes only a part of a larger population, the quantitative thresholds in criteria A-D (and even E, depending on how the analysis is made) might not accurately reflect the extinction risk. Also, a global extinction is final, while an extinction from a country may later be followed by a recolonization. While the new system has a clear definition for species that are Extinct (EX) or Extinct in the Wild (EW), it lacks a definition for Regionally Extinct (RE) species. The time frame considered when creating the definition of RE will effect the listings.

The time frame is also important when considering the categories Critically Endangered (CR), Endangered (EN) and Vulnerable (VU) on a regional level. When assessing the prospects for the next 10 years, for example, a species may face an extinction risk in a country of more than 50% (CR). However, if these prospects are assessed over a period of 100 years the extinction risk for the same species might still be 50% (then corresponding to VU), because there are interactions with populations outside the country.

Hypothetical Cases

In Figure 1 the species is represented in the country only by a marginal part of a larger distribution area. The extinction risk within the country may be less than what the criteria A-D(-E) applied on the national part of the population suggest (compared to when applied on a global level), because if the species tends to die out within the country, new individuals from neighboring countries may move in (rescue effect). However, in rare instances, the reverse situation might be the case. If the marginal population is not self-sustaining and depends on regular immigration from the more central parts of the geographic range, the extinction risk within the country could be higher than is suggested by criteria A-D(-E), if something threatens the central population. In both cases, however, the extinction risk depends on the adopted time frame. Over a short time perspective the species may face a high extinction risk, but in a longer perspective there is a good possibility of recolonization and survival.

In the next case (Figure 2), the population in the country is geographically separated from other populations. If there is no flow of individuals between the populations, the new IUCN criteria are applicable, because populations outside the country do not affect the extinction risk within the country. If, on the other hand, there is a source-sink situation with a regular inflow of individuals, we have a similar situation to that shown in Figure 1. Again, the extinction risk depends on the time frame. In the case of an isolated self-sustaining population, the extinction risk may be low over a short time span, but very high over a longer time span, while the reverse may be the case in the source-sink situation.

Proposals on a Regional Scale

The obstacles to applying the new IUCN Red List criteria on a national level, as presented above, may seem very difficult to address, but I think they can be managed.

The majority of threatened species are so because they have small and isolated populations. If they do not have a high dispersal ability, the application of the IUCN criteria is straightforward. The problems will mainly arise among highly mobile organisms, such as birds, larger mammals, certain insects, many marine organisms, and maybe cryptograms with easily dispersed spores. The problems will of course be more pronounced in countries surrounded by other countries than in those surrounded by sea or other barriers preventing dispersal.

Conceptually, one could possibly cope with the impact of neighboring populations by quantifying the flow of individuals (or diaspores) across the borders (IUCN 1995) and include this in a metapopulation model. However, in reality, we often lack such data. If we do have such data and are able to include it into a quantitative analysis, we can use criterion E. Because of the possibility of regional extinction, as well as the problems with the time frame, we must then add a passage to the definition of the E criterion of categories CR-VU. The current definition of CR under criterion E is:

Quantitative analysis showing the probability of extinction in the wild is at least 50% within 10 years or 3 generations, whichever is the longer

At a regional level, this criterion could read:

Quantitative analysis showing the probability of regional extinction, that will persist for at least100 years from now, is at least 50% within 10 years or 3 generations, whichever is the longer.

In the majority of cases we lack such data and the solution must be to evaluate the population within the country against the IUCN criteria A-D, starting with the assumption that the national population is the only one in the world. Then, one should check the situation of the species against a list to determine whether or not any factors influence its extinction risk. Such a checklist should include at least the following items:

• Does the national/regional population have any obvious contact with populations outside the borders? What is the distance to the nearest population? Are there any effective barriers preventing dispersal to and from neighboring populations?

• Is the species capable of long-distance dispersal? Is it known to do so?

• How abundant is the species in neighboring regions? Are the populations there stable, increasing or decreasing? Are there any important threats to those populations?

• Are there any known differences in local adaptation between the national and foreign populations, i.e. is it probable that the foreign populations are adapted to survive within the country?

• What is the environmental (including climatological) situation within one’s own country/region for the species? Is the national population self-sustaining (has it shown a positive reproduction rate over the years) or is it dependent on immigration for its long-term survival?

• Are environmental conditions in the country such that immigrating specimens are able to establish or has the species disappeared because these prerequisites were not fulfilled?

• If the species becomes extinct in the country, what are the probabilities for recolonization within 100 years?

If an evaluation of these questions indicates that foreign populations affect the extinction risk of the national population in such a way that it is lower or higher than the A-D criteria suggest, the threat category should be adjusted downwards or upwards. Such a movement must be indicated, e.g. by giving the category met by the global criteria within parenthesis. Thus EN (VU) would indicate that the species met the criteria for VU, but was moved upwards (probably a very rare situation) to EN, while EN (CR) indicates that it has been moved downwards (much more likely) from CR.

In the case where there is not enough data for such an evaluation, or the result is uncertain, the species should be placed in the category met by the global criteria.

It is worth noting that a neighboring population more often will affect the national category when the criteria B1, B3 and D are met (no observation of decline) than when criteria A, B2 and C are fulfilled (a decline has been observed). This is because if there is an observed decline, the decline happens in spite of any influence from populations outside the country (though the decline might have been even bigger without such an influence). Once again, the time frame is problematic, since there can be a decline in the country that, later on, can be balanced by immigration.

Other Red List Categories

The three Lower Risk (LR) subcategories, conservation dependent (cd), near threatened (nt) and least concern (lc), can be treated as defined by IUCN (1994) after having taken above mentioned considerations for CR-VU. The categories Data Deficient (DD) and Not Evaluated (NE) can be applied at national level without any adaptations.

As indicated earlier in this paper, it may be necessary to define a new category for species extinct only within a country or another region. An extinction of an endemic species in a country is equal to a global extinction, but when a more widespread species becomes extinct within a country, it still survives in other parts of the world. These two different kinds of extinction deserve to be recognized and distinguished in national Red Lists. This has already been done in some countries, and national extinction has been described by words such as Extirpated or Vanished. However, Vanished may be perceived as too weak a word, and Extirpated has the double disadvantage of alluding to deliberate human-induced eradication (which rarely is the case) and being confused with the category Extinct when abbreviated. The most appropriate term would probably be Regionally Extinct (RE).

Conservation Priority

The IUCN Red List categories do not allow for any considerations other than extinction risks. However, there may also be other criteria that are important when coming to the decision about national conservation measures (Sparrowe and Wight 1975, Nieme 1982, Millsap et al. 1990, Daniels et al. 1991, Master 1991, Forey et al. 1994, Gärdenfors in press). As suggested in the IUCN guidelines (IUCN 1994, p. 8, section 11), and also by Avery et al. (1995), two important criteria could be global status and proportion of the global population or range that occurs within the region.

The global scale may not be the most appropriate for comparison with a national scale. A species scattered in fragmented populations over the entire Holarctic region is probably genetically considerably differentiated and the populations in North America and Eastern Europe most probably are not interchangeable. As a general rule, the most appropriate scale would probably be the continental or comparable biogeographic regional scale. The proportion of the international/continental population and probability of recolonization can be given on a scale from 0 to 1 (where the intervals for population percentages depend on the area of the country in relation to the continental area, Figure 3).

In a priority-setting system, many other criteria could be of interest, such as ecological importance, historical importance, taxonomic and genetic importance, importance to people, etc. Most of these, however, turn out to be problematic to apply, either conceptually or in practice (Gärdenfors in press) and are consequently difficult to include in a formalized priority-setting system. However, in cases where any such criterion is obviously important, it could be remarked upon separately.

Taking into consideration the points made above, a national Red List could have an appearance as in Figure 4. It is not obvious how to weigh the individual criteria against each other. Maybe the best solution is to avoid any such a priority weighting, and allow for different weighting when different situations and issues come up.

How to Proceed?

In order to develop guidelines for applying the IUCN Red List categories at regional levels it is now necessary to produce and distribute draft guidelines and test them against a wide variety of species in many countries in different parts of the world. It is important that this procedure involves a very wide consultation of national Red List compilers from throughout the world. Hopefully IUCN will be able to adopt and publish a set of official guidelines in the near future.

Acknowledgements
Ingemar Ahlén, Jonathan Baillie, Oskar Kindvall, Georgina Mace and Simon Stuart provided many constructive suggestions, which substantially improved this manuscript.

Ulf Gärdenfors, Ph.D.
Assistant Director
Swedish Threatened Species Unit
P.O. Box 7002
S-750 07 Uppsala
Sweden

References

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© 1996 IUCN. Reprinted from the 1996 IUCN Red List of Threatened Animals.