COSEWIC Guidelines on Manipulated Populations

Approved by COSEWIC in April 2010

In response to the increasing numbers of wildlife species whose distribution or genetic make-up have been manipulated by humans, deliberately or accidentally, these guidelines have been developed to assist COSEWIC in determining the eligibility of populations for inclusion in wildlife species status assessments.

COSEWIC normally only considers native wildlife species for assessment (see Definitions and Abbreviations), see also COSEWIC’s Assessment Process and Criteria) and excluding wildlife species introduced to Canada via human intervention. COSEWIC's Assessment Process and Criteria provides no clear direction for the assessment of native wildlife species that include (re-) introduced, hybrid, supplemented or captive populations. The SARA (and COSEWIC) definition of wildlife species includes the term ‘wild by nature’ which, according to some legal interpretations, might include captive individuals with recent wild ancestors. The IUCN, which COSEWIC consults for guidance as necessary, provides advice on the assessment of introduced or re-introduced populations, as discussed in section 1 below; however, advice for other types of manipulated populations is not explicit.

Prohibitions specified by SARA apply to individuals in the population identified and assessed by COSEWIC.  Clear definition of whether wild and manipulated components are part of the assessed population (the “wildlife species” in SARA terminology), is essential to determining which individuals or components would be subject to prohibitions.  This determination must be made based on whether manipulated populations are genetically or geographically distinct from populations in the wild (i.e. meets definition of Designatable Unit).

Some manipulated populations may be genetically distinct, depending on the number of generations over which they have been manipulated. Other manipulated populations, for which sufficient time may not have elapsed for genetic differences to have accumulated, might be considered geographically distinct.  COSEWIC's Guidelines for Recognizing Designatable Units describes the degree to which a population must be different from other populations to warrant a separate Designatable Unit status. In particular, range disjunction arising when "dispersal of individuals between separated regions has been severely limited for an extended period of time and is not likely in the foreseeable future" is one key criterion. Thus, if a manipulated population has been established for reasons other than conservation, such as for commercial purposes, and the conditions of confinement are such that it is not possible for individuals in captivity to interbreed with wild population(s), then the manipulated population might be considered by COSEWIC to be geographically distinct, and identified as such in the wildlife species status report.

Two types of considerations related to manipulated populations must be addressed in COSEWIC status assessments:

1. Is the manipulated population part of the wildlife species (or Designatable Unit) being assessed?  

2. Should individuals from the manipulated population be included when applying quantitative criteria to determine status (i.e. based on decline rates, on numbers of mature individuals)?

These guidelines clarify COSEWIC’s position on whether or not manipulated populations are to be part of the wildlife species being assessed, as well as on inclusion of such populations for application of quantitative criteria where they are considered part of the wildlife species. Given the breadth of taxonomic groups, some degree of flexibility needs to be retained in the application of the guidelines to allow for the consideration of specific circumstances associated with different species. In addition, the long-term consequences of various manipulations of wildlife species are often difficult to predict; thus, uncertainty should be addressed in a conservative manner.

These guidelines consider four types of manipulated populations:

1. introduced/re-introduced

2. hybrid

3. supplemented

4. captive

Genetically modified organisms will always be excluded from wildlife species status assessments, although they may be identified as a threat. Table 1 summarises the following guidelines as they apply to the four types of manipulated populations.

Guideline #1: Wildlife species status reports will clearly identify and describe manipulated populations and indicate whether or not they are part of the wildlife species being considered for status assessment and why (as per Table 1). Where they are considered to be part of the wildlife species, the status report will also clearly indicate if the manipulated populations are included in the application of quantitative criteria and why (as per Table 2). Status reports should also describe the history of changes in assessed wildlife species due to the manipulations listed above.

Guideline #2: COSEWIC will generally¹ not consider as part of the wildlife species being assessed, any manipulated populations established for purposes other than species conservation (for example, those established for commercial purposes) provided the population is geographically or genetically distinct from the wildlife species under assessment, and there is no intention that the population contribute to the wild population. Under such a scenario, COSEWIC will clearly indicate why the population is excluded.

1. Introduced/Reintroduced Populations

Numerous plant and animal species have been either introduced to new areas within (intra-limital) or outside (extra-limital) their natural range or reintroduced to areas they previously occupied within their natural range as a result of intentional or unintentional human activities. The decision about whether to include such established, (re)introduced populations as part of the wildlife species being assessed may depend on whether or not the introduction is intra-limital or extra-limital and on its predicted or demonstrated impact on the wildlife species in its natural range and on other components of biodiversity.

i) Reintroductions occur within the natural range and in the natural habitat of a wildlife species. They may include translocations (establishment in a new area, using wild individuals from another area within the natural range) or reintroductions to an area where a wildlife species has been extirpated. Reintroductions may include populations established from escaped or intentionally transplanted, captive-reared/maintained populations that themselves were established using individuals from within the natural range of the wildlife species. For example, Swift Foxes were reintroduced to the Canadian prairies using both captive-reared and wild-caught foxes from American prairie states. Similarly, captive-bred Peregrine Falcons were released in parts of Canada where they had been extirpated.

Regardless of the intent or means of the original introduction (conservation-based or not, intentional or not), the IUCN recommends that self-sustaining populations resulting from translocations and reintroductions be included in wildlife species assessments (Standards and Petitions Working Group 2006).

Guideline #3:COSEWIC will include all intra-limital reintroductions, regardless of intent, as part of the wildlife species being assessed. However, COSEWIC will generally only include such populations in the application of quantitative criteria to establish status where the population is predicted or demonstrated to have a net positive impact on the wildlife species being assessed. A net positive impact would result in an increase in the average fitness of individuals of the wildlife species (reflected, for example, by an increased probability of survival, increased population growth rate, and/or increased ability to adapt to environmental change).

(ii) Extra-limital introductions are outside the historical range of the wildlife species and may originate from translocated wild individuals or captive-reared individuals. For example, Westslope Cutthroat Trout populations in the North Saskatchewan and Ram River drainages of Alberta, established using hatchery-reared individuals, are outside the historic range of the wildlife species.

The IUCN includes populations resulting from extra-limital introductions as part of species assessed if the intent of those introductions was for conservation and if there is no suitable habitat remaining within the historic range of the wildlife species. These are considered benign introductions.

Guideline #4: COSEWIC will generally only include populations resulting from benign extra-limital introductions as part of the wildlife species being assessed if there is no suitable habitat remaining within the natural range of the wildlife species in Canada. Under such a scenario, the population may warrant a separate Designatable Unit when it is considered geographically disjunct from the native range. For introductions included as part of the wildlife species being assessed, quantitative criteria to assess status will also be applied where a net positive impact on the wildlife species is predicted.

2. Hybrid populations

Interbreeding can occur along a continuum ranging from between individuals from different populations of the same taxonomic species to between individuals from different biological species. Rhymer and Simberloff (1996) define hybridization as ‘interbreeding of individuals from what are believed to be genetically distinct populations, regardless of the taxonomic status’. Although hybridization usually refers to mating between heterospecific individuals, it can also apply to mating between individuals of different sub-species or genetically differentiated populations. There is no universally accepted biological species concept (Hey 2006, Haig et al. 2006), and the definition of subspecies is even more controversial (Haig et al. 2006). Consequently, the level of hybridization should not define a rigid threshold for assessment or conservation purposes. Rather, when considering hybrid populations for assessment, the consequences of the hybridization should be examined from an evolutionary perspective. The more genetically differentiated the two groups, the greater the probability of consequences such as outbreeding depression and the loss of adaptive gene complexes. Alternatively, for small populations where inbreeding depression is evident, introductions of novel genotypes from non-native sources may be beneficial. Natural hybridization and gene flow play an important role in the continuing evolution of some organisms and in the maintenance of genetic diversity. The following sections consider these concepts further in the context of two types of mechanisms resulting in hybridization.

(i) Natural hybridization - Some hybridization (i.e., the production of offspring as a result of interbreeding between recognized biological species or subspecies) occurs independently of human activities and may result in new biological species or novel recombinant genotypes (see references in Stein and Uy 2006, also Seehausen 2004). Hybrid zones in which two closely related taxa naturally overlap in distribution occur in several taxonomic groups and may remain stable when parental genotypes maintain their integrity (Hagen and Taylor 2001) or continue to change (unidirectional introgression, Stein and Uy 2006). Furthermore, hybridization is considered a common feature of parapatric or sympatric divergence (Mallet 1995), and it can be followed by stabilization and perpetuation of the hybrid derivative as a distinct taxonomic entity (Stebbins 1969). One example of natural hybridization is that between Steelhead Trout and Coastal Cutthroat Trout, where the two wildlife species naturally occur together, and the Misty Lake Stickleback, where ‘intermediate’ hybrid forms between the stream and lake ecotypes are part of the evolutionary process. Hybrids resulting from interbreeding between the wildlife species under assessment and cultivated individuals (see Definitions and Abbreviations) originating from the same wildlife species are not considered to be the product of natural hybridization (e.g. interbreeding of wild and escaped farmed Atlantic Salmon).

Guideline #5: Populations undergoing natural hybridization are eligible for inclusion as part of the wildlife species being assessed by COSEWIC. Mature individuals could, in this case, include hybrids and be included in the application of quantitative criteria.

(ii) Human-mediated hybridization – Hybridization can be a direct or indirect consequence of human activities. Activities affecting hybridization directly include the introduction of individuals from a genetically distinct population into the natural range of another genetically distinct population or the intentional crossbreeding of two genetically distinct populations, regardless of taxonomic status. Human activities that can indirectly lead to hybridization include the destruction or modification of suitable habitat and the removal of reproductive barriers (including geographical, physical or behavioural) that previously existed between the two genetically distinct native populations.

The result of the initial hybridization event between two pure parental genotypes is an F1 hybrid. Hybrids may be sterile, have reduced fitness, or be fully capable of breeding with other F1s or of backcrossing with parental genotypes. Although hybrids that are sterile or have low fitness may not affect the genetic composition of the pure populations, they represent a loss to production and may pose a risk to the viability of at least one parental population, particularly if it is small. Backcrossing and continued successful breeding can lead to increasing levels of genetic introgression resulting in: (1) hybrid swarms where neither of the original pure genotypes exists or (2) unidirectional introgression with the loss of one of the pure parental populations.

Where human-mediated hybridization occurs, F1 hybrids and their introgressed progeny should generally be considered a loss to the wildlife species and a threat to its persistence; hybrids do not represent either original taxonomic group, and they do not contribute to the evolutionary lineage of either group. For example, many populations of Westslope Cutthroat Trout in Alberta have experienced introgression of genes from artificially introduced Rainbow Trout and Yellowstone Cutthroat Trout. However, for closely related taxa, it may be difficult to differentiate between ancient polymorphisms shared by the two groups and low levels of introgression. For example, Allendorf et al. (2004) proposed an introgression threshold for westslope cutthroat trout populations; a population may be considered genetically pure if it expresses <1% admixture (i.e. 1% or fewer of a sample of alleles from a population of putatively pure species “A” can be attributed to introgression with species “B”).  This threshold should be assessed using assays from an adequate sample of diagnostic selectively neutral molecular markers and individuals that results in at least a 95% probability that a minimum 1% introgression will be identified if it is occurring in the population.

Guideline #6: If introgression is known or suspected, COSEWIC will consider whether it is likely to negatively affect the conservation of the wildlife species. A net negative impact is one predicted to result in a reduction in the average fitness of individuals of the wildlife species being assessed (reflected, for example, by a reduced probability of survival, reduced population growth rate, and/or reduced ability to adapt to environmental change). Under these circumstances, F1 hybrids, if identifiable, and their progeny would not be included as part of the wildlife species being assessed. Where introgression in a population is considered extensive, it may be prudent to exclude the entire population from the wildlife species being assessed. Instead, these populations may be identified as a threat to the wildlife species.

Exceptions may exist where the gene pool of a wildlife species is so small that inbreeding depression is evident, and genetic variability cannot be increased using individuals from the same genetic pool. In such situations, it may be prudent to interbreed the wildlife species with another closely related population of the same wildlife species to increase genetic variability and benefit from hybrid vigour, particularly where the wildlife species in question is otherwise expected to go extinct. This will at least preserve some of the genetic composition of the wildlife species and may restore its ecological role. However, the resultant recombinant population may be assessed as a separate Designatable Unit, with the original one considered extinct, if interbreeding occurred with individuals from other Designatable Units or wildlife species. Furthermore, this recombinant population would only be eligible if it is not dependent on continued introductions to persist and it does not pose a threat to the donor wildlife species contributing to the interbreeding efforts.

3. Supplemented Populations

Supplemented populations are native populations that receive captive bred/reared (or cultivated) individuals or wild-to-wild translocations, intentionally or unintentionally. Supplementation is accomplished using individuals originating from the same biological species.  

Supplementation is frequently undertaken to provide harvestable individuals. Supplementation has also been used to rebuild depressed or genetically depauperate populations, as is being attempted with captive reared Vancouver Island marmots. Unplanned supplementation may occur if individuals escape from captivity or cultivation and contribute to recruitment in a wild population. There is also a conservation technique known as ‘head-starting’, which involves keeping individuals from natural populations in captivity (either in-situ or ex-situ) during a particularly vulnerable life stage, usually near birth or germination. For example, head-starting can decrease predation on Caribou calves.

Guideline #7: Regardless of the intent of supplementation, all supplemented populations will be considered to be part of the wildlife species being assessed.  Where possible to identify, individuals used to supplement wild populations and resultant naturally-produced offspring should generally only be included in the application of quantitative criteria to establish population status if these individuals are predicted to have a net positive impact on the wildlife species being assessed. These individuals should not be counted if there is evidence of reduced fitness or genetic characteristics that may corrupt local adaptations.

4. Captive or Cultivated Populations

Captive and cultivated populations may be maintained for ex situ conservation or commercial purposes. For example, captive breeding might be an integral component of recovery programmes for wildlife species unable to survive in the wild under current conditions. Reproduction may or may not be based on pedigree tracking, and human intervention may be required for successful breeding. Such populations may be founded by wild-caught individuals from a single source, or result from the mixing of disparate genetic sources, some of which may have been subjected to artificial selection. For example, captive-breeding programmes of Swift fox, Peregrine Falcon and Vancouver Island Marmot either are or have been in place in Canada in the recent past. Artificial selection for traits best suited to captivity begins immediately upon being contained in a captive environment (e.g. Lynch and O’Hely 2001); this is called domestication selection. The greater the number of generations in captivity, the greater the effect of domestication is on heritable traits and non-heritable, learned behaviours. Although efforts to minimize domestication have been made in some conservation-based captive breeding programmes, such changes are impossible to prevent entirely. Regardless, where populations are maintained in captivity for conservation purposes, the intent to release individuals into the wild at some time exists.

Guideline #8: Generally, captive and cultivated populations held for conservation purposes will be included as part of the wildlife species being assessed. These populations will, however, be excluded from the application of quantitative criteria to establish status. The term ‘extirpated’ may be used in assessment for wildlife species that only exist in captivity. Note that Guideline #2 indicates COSEWIC’s position on captive and cultivated populations established for commercial purposes.

For example, animals maintained in zoo facilities would be included as part of the wildlife species being assessed but their numbers would not be counted in population estimates. The Vancouver Island Marmot Recovery Centre maintains captive marmots which are bred and released into natural habitats periodically. Captive held individuals would be included in the wildlife species being assessed but not as part of the population size estimate given that their contribution to the wild population cannot be confirmed.

Table 1. Summary of types of population manipulations and associated Guidelines.

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¹When significant threats (e.g. poaching, disease) affecting a wildlife species at risk are likely to be exacerbated by manipulated populations, the manipulated populations should clearly be considered as a threat to the wildlife species at risk.

²Based on IUCN definition of benign introduction.

References :

Allendorf, F., R. Leary, N. Hitt, K. Knudsen, L. Lundquist and P. Spruell. 2004. Intercrosses and the U.S. Endangered Species Act: should hybridized populations be included as Westslope cutthroat trout? Conservation Biology 18:1203-1213.

Boyer, M. 2006. Rainbow trout invasion and the spread of hybridization with native Westslope cutthroat trout. M.Sc. Thesis, University of Montana.

Hagen, J. & Taylor, E.B. 2001. Habitat partitioning as a factor limiting gene flow in hybridizing populations of Dolly Varden char (Salvelinus malma) and bull trout (S. confluentus). Canadian Journal of Fisheries and Aquatic Sciences 58: 2037–2047.

Haig, S., E. Beever, S. Chambers, H. Draheim, B. Dugger, S. Duhham, E. Smith, J. Fontaine, D. Kesler, B. Knaus, Iara Lopes, P. Loschl, T. Mullins and L. Sheffield. 2006.
Taxonomic considerations in listing subspecies under the U.S. Endangered Species Act. Conservation Biology 20:1584-1594.

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IUCN. 1998. Guidelines for re-introductions. Prepared by the IUCN/SSC Re-introduction Specialist Group, IUCN, Gland, Switzerland and Cambridge. UK. 10 p.

Lynch, M. and M. O’Hely. 2001. Captive breeding and the genetic fitness of natural populations. Conservation Genetics 2:363-378.

Mallet, J. 1995. A species definition for the modern synthesis. Trends Ecological Evolution 10: 294-299.

Rhymer, J. and D. Simberloff. 1996 Extinction by Hybridization and Introgression. Annual Review of Ecology and Systematics 27:83-109.

Seehausen, O. 2004. Hybridization and adaptive radiation. Trends in Ecology and Evolution 19:199-207.

Standards and Petitions Working Group. 2006. Guidelines for using the IUCN Red List Categories and Criteria. Version 6.2. Prepared by the Standards and Petitions Working group of the IUCN SSC Biodiversity Assessments Sub-Committee in December 2006.

Stebbins, G. 1969. The significance of hybridization for plant Taxonomy and evolution. Taxon, Vol. 18, No. 1, Smithsonian Summer Institute in Systematics 1968, Part 1 (Feb., 1969), pp. 26-35

Stein, A. and A. Uy. 2006. Unidirectional introgression of a sexually selected trait across an avian hybrid zone: a role for female choice? Evolution 60:1476-1485.