Appendix S1. Prioritization approaches in practice: What are they used for?
Even though threatened species lists are not designed for species prioritization, often these are used straightforwardly to assign legal protection status to species. Some countries have developed their own prioritization schemes specifically for that purpose (some examples in de Grammont and Cuaron 2006).
Identifying focal species for conservation action
The simplest form of prioritization is to identify as focal species only the ones that are of conservation interest, while ignoring the other species. For example, only threatened, rare, endemic or keystone species may be considered (Ceballos and Ehrlich 2006). However, often the use of a specific group is due to assumed surrogate relationships with other species (e.g., Das et al. 2006), rather than to preference for one group over the others.
Assigning conservation targets
Targets for conservation, usually as percentage of individuals, populations or distribution to be protected, can be assigned differently according to species priorities. Targets are frequently assigned based on threat category or various forms of rarity, but more specific population parameters can also be used when available (Pressey et al. 2003).
Species weights in systematic conservation planning
Certain reserve selection approaches allow for the use of differential species weights. These approaches operate in terms of maximization of “conservation value” across selected sites, which depends on the weights of the species that occur at the sites (Arponen et al. 2005; Early and Thomas 2007; Kremen et al. 2008), rather than relying on mere species richness and fixed targets.
Maximizing persistence of diversity directly in systematic conservation planning
This can be seen as prioritization in the sense that species contribute differentially to total diversity. Any diversity measure can be incorporated directly in the objective function in systematic conservation planning, for example phylogenetic diversity (Polasky et al. 2001; Forest et al. 2007). In practice, reserve sites are selected in order to maximize the (persistence of the) diversity measure instead of maximizing species richness (see also Fig. 1).
Appendix S2. Assessing extinction risk
Some examples of methods for assessing extinction risk, that have then been used to assign conservation priorities. More comprehensive reviews of assessing extinction risk are Andelman et al. (2004) and DeGrammont and Cuaron (2006).
IUCN Red List (IUCN 2001)
A rule-based system. The oldest (1966) of threat classification systems, but has been frequently updated. The scheme is applicable to all macro-fauna and flora. Created for global scale use, but guidelines for application at regional levels were published in 2003. It is considered the most robust system (de Grammont and Cuaron 2006) because it uses quantitative criteria which are based on population biology (life history, habitat requirements, abundance, distribution, threats, any specified management options of that species). The threat categories are defined only in terms of extinction risk over explicit, increasing time periods. The list itself is produced by a network of over 7000 species experts.
Being the most widely applied system, it has provoked much discussion. It has been criticized and praised even for the same qualities: Being rule-based implies low data requirements, but also that it does not take advantage of all available data – a species that nearly fulfils several criteria for being classified as endangered is in the same category with a species that barely meets one criterion for being vulnerable (Mace et al. 2006). Another positive feature of a rule-based system is that it is explicit about which features of a species led to its listing (Mace et al. 2006). It also provides guidance on how to deal with uncertainty when applying the criteria (see also Akçakaya et al. 2000; Regan et al. 2000).
Criteria include: Population size and size reduction, extent of occurrence or area of occupancy, quantitative analysis of extinction risk, degree of fragmentation, extreme population fluctuations, and skewed population structure.
Risk categories: extinct (EX), extinct in the wild (EW), critically endangered (CR), endangered (EN), vulnerable (V), near threatened (NT), least concern (LC)
NatureServe Conservation Status (NatureServe 2008)
A rule-based system, with the difference to the IUCN scheme that all criteria are taken into account in classification. It is applicable at any geographical scale, and to communities and ecosystems in addition to species. Most criteria are defined numerically, and data requirements are high, although both empirical data and expert opinion can be used as data inputs.
Criteria include: number and condition of occurrences, population size, range extent, area of occupancy, short- and long-term trends in all above mentioned factors, threats (scope, severity, and immediacy), intrinsic vulnerability, number of protected and managed occurrences, and environmental specificity.
Risk categories: critically imperilled, imperilled, vulnerable to extirpation or extinction, apparently secure, and demonstrably widespread, abundant and secure (and a number of additional categories for special cases such as species of only historical occurrence or with insufficient information).
Conservation Priority Index (Cofré and Marquet 1999)
A point scoring method. Applicable at all geographical scales, although initially created for national use (Chile). It differs from the previous systems also in that it is mostly based on (anthropogenic) threats and species intrinsic characteristics instead of population trend data, which the authors claim are often hard to acquire. Consequently, it evaluates potential vulnerability rather than actual extinction risk (de Grammont and Cuaron 2006). It is not a pure threat assessment technique but a prioritization scheme that combines for example “taxonomic singularity” with extinction risk. It is flexible regarding data requirements (some criteria are quantitative, some not), but also problematic in that some criteria are redundant.
Criteria include: number of ecoregions where species is found, geographic distribution within Chile, local abundance, degree of endemism, taxonomic singularity, body mass, presence on IUCN list, effect of human activities, and degree of protection.
Risk categories: No categories. Species are assigned a “priority index” which is the sum of scores for all criteria, ranging from zero to 27, with species scoring at least 12 considered as priority.
Appendix S3. Combining different criteria
This appendix does not attempt to cover the extensive literature on multi-criteria analyses that can and often do combine species-level criteria with any other kinds of criteria, ranging from reserve connectivity to cultural heritage value. These are reviewed elsewhere (Moffett and Sarkar 2006). Instead, I give a few examples of typical ways of combining different species-level criteria into a single score or objective.
Additive scoring approaches
Species scores are (often weighted) sums of scores given based on different criteria. One of the most comprehensive approaches regarding the criteria used is Marsh et al. (2007): Extinction risk, consequences of extinction (including factors such as uniqueness of ecological role, genetic and taxonomic uniqueness) and potential for successful recovery (including knowledge of and capacity to control threatening processes, costs of conservation action and biological recovery potential). Other examples include e.g. Cofré and Marquet (1999) and Keith et al. (2007). Summing of scores is problematic because criteria may be correlated and some factors therefore “inflated”, and for instance, if a species has zero potential of recovery, it may still receive a relatively high score due to high impact of its extinction.
Multiplicative scoring approaches
Multiplication implies that all criteria are important and do not independently influence species’ priority, for example, only the species which are both unique and in need of protection receive high weights, and neither criterion alone is enough. Multiplying an indicator of extinction risk with a proxy of uniqueness is essentially an estimate of expected loss if no conservation actions are taken. Arponen et al. (2005) derive species weights by multiplying a “taxonomic uniqueness” score with a threat score (a weighted sum of scores derived from Red List classifications and a measure of national rarity). Also the EDGE score (Isaac et al., 2007) falls within this category. See also the approaches to evaluate expected loss of biodiversity by Witting and Loeschke (1995) and Redding and Mooers (2006). This way only the species which are both unique and in need of protection receive high weights, and neither criterion alone is enough.
Species’ contribution to “future expected diversity”
Weitzman’s (1998) species ranking index gives the contribution of a species to “future expected diversity”. It maximizes numbers of features (genes) across species taking account of probabilities of extinction and costs of changing them, as well as species “utility” estimations (species value per se, irrelevant from a biodiversity viewpoint). Regarding how species uniqueness is considered, this measure does not differ essentially from previous approaches (e.g., Faith 1992). This approach combines costs and effectiveness of conservation actions, and species’ dissimilarities, but ignores differential quantities of features carried by species. The approach has recently been further refined and applied by Joseph et al. (2009) by the name “Project Prioritization Protocol” to produce rankings of species-specific conservation projects. Approaches to solving this computationally difficult problem are discussed in Hartmann and Steel (2006).
Species’ differential contribution to conservation benefit in systematic conservation prioritization
Instead of producing species scores or rankings, or ranking of conservation projects, species’ differential contribution to conservation benefit can be directly accounted for in systematic conservation prioritization (see also Appendix S1 and Fig. 1). Mace et al. (2006) maximize the number of species surviving. This approach combines costs and effectiveness of conservation actions, but ignores species’ differential contribution to total diversity (uniqueness). Others maximize phylogenetic diversity considering also number or area of reserves as surrogate for conservation costs, but ignore need and effectiveness of protection (Polasky et al. 2001; Forest et al. 2007)
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