Table 8. COSEWIC definitions associated with quantitative criteria
Area of Occupancy: The area within 'extent of occurrence' that is occupied by a taxon, excluding cases of vagrancy. The measure reflects the fact that the extent of occurrence may contain unsuitable or unoccupied habitats. In some cases (e.g. irreplaceable colonial nesting sites, crucial feeding sites for migratory taxa) the area of occupancy is the smallest area essential at any stage to the survival of the Wildlife Species/designatable unit considered (in such cases, this area of occupancy does not need to occur within Canada). The size of the area of occupancy will be a function of the scale at which it is measured, and should be at a scale appropriate to relevant biological aspects of the taxon, the nature of threats and the available data. To avoid inconsistencies and bias in assessments caused by estimating area of occupancy at different scales, it may be necessary to standardize estimates by applying a scale- correction factor. Different types of taxa have different scale-area relationships. (Source: adapted from IUCN 2010)
Continuing decline: A recent, current or projected future decline (which may be smooth, irregular or sporadic), which is liable to continue unless remedial measures are taken. Fluctuations will not normally count as continuing declines.
Estimated continuing decline (under criterion C1) had quantitative thresholds and requires a quantitative estimate, Which can be calculated using the same methods as for population reduction.
Under criteria B1b, B2b, and C2, continuing declines can be observed, estimated, inferred or projected. Although not explicitly mentioned in criteria B or C2, estimated continuing declines are permissible. Under criterion C1, continuing declines can only be observed, estimated or projected. A continuing decline under criteria B or C can be projected, thus, it does not have to have started yet. However, such projected declines must be justified and there must be high degree of certainty that they will take place (i.e., merely 'plausible' future declines are not allowed).
Continuing declines need not be continuous; they can be sporadic, occurring at unpredictable intervals, but they must be likely to continue into the future. Relatively rare events can be considered to contribute to a continuing decline if they happened at least once within the last three generations or 10 years (whichever is longer), and it is likely that they may happen again in the next three generations or 10 years (whichever is longer), and the population is not expected to recover between the events.
If habitat is declining (in area or quality) but abundance is not, this may be because (i) there is a delay in the population's response to lower carrying capacity, perhaps because the population is below the carrying capacity for other reasons (such as harvest), (ii) habitat is declining in areas not currently occupied by the taxon, or (iii) habitat is not correctly identified. In the case of (i), the population will eventually be impacted; in the case of (ii) the loss of recolonization options may eventually impact the population. In both cases, criteria B1b(iii) or B2b(iii) may be invoked even if the population is not undergoing a continuing decline. (Source: IUCN Standards and Petitions Subcommittee 2019).
For more guidance on the concept of “Continuing Decline” see the most recent versions of the IUCN Guidelines.
Demographic Stochasticity: Random variation in demographic variables, such as birth rates and death rates, sex ratio and dispersal, for which some individuals in a population are negatively affected but not others. In small populations, these random events increase the risk of extinction.
Environmental Stochasticity: Random variation in physical environmental variables, such as temperature, water flow, and rainfall, which affect all individuals in a population to a similar degree. In small populations, these random events increase the risk of extinction.
Estimated: Information that is based on calculations that may include statistical assumptions about sampling, or biological assumptions about the relationship between an observed variable (e.g., an index of abundance) to the variable of interest (e.g., number of mature individuals). These assumptions should be stated and justified in the documentation. Estimation may also involve interpolation in time to calculate the variable of interest for a particular step (e.g., a 10-year reduction based on observations or estimations of population size 5 and 15 years). (Source: IUCN 2010)
Extent of Occurrence: The area included in a polygon without concave angles that encompasses the geographic distribution of all known populations of a Wildlife Species.
Extreme Fluctuation: Changes in distribution or in the total number of mature individuals of a Wildlife Species that occur rapidly and frequently, and are typically of more than one order of magnitude. (Source: adapted from IUCN 2010).
Generation: Generation length is the average age of parents of a cohort (i.e. newborn individuals in the population). Generation length therefore reflects the turnover rate of breeding individuals in a population. Generation length is greater than the age at first breeding and less than the age of the oldest breeding individual, except in taxa that breed only once. Where generation length varies under threat, the more natural, i.e. pre-disturbance, generation length should be used. (Source: adapted from IUCN 2010). Revised guidance on calculating generation length is available in section 4.4 of IUCN 2011.
Inferred: Information that is based on indirect evidence, on variables that are indirectly related to the variable of interest, but in the same general type of units (e.g., number of individuals or area or number of subpopulations). Inferred values rely on more assumptions than estimated values. Inference may also involve extrapolating an observed or estimated quantity from known subpopulations to calculate the same quantity for other subpopulations. Whether there are enough data to make such an inference will depend on how large the known subpopulations are as a proportion of the whole populations, and the applicability of the threats and trends observed in the known subpopulations to the rest of the taxon. The method of extrapolating to unknown subpopulations depends on the criteria and on the type of data available for the known subpopulations. (Source: IUCN 2010).
Location: The term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat. Where the most serious plausible threat does not affect all of the taxon’s distribution, other threats can be used to define and count locations in those areas not affected by the most serious plausible threat. (Source: IUCN 2010, 2011). In the absence of any plausible threat for the taxon, the term “location” cannot be used and the subcriteria that refer to the number of locations will not be met. See also “Rapidly (in regards to “Locations”). (Source: IUCN 2010, 2011).
Mature Individuals (Number of): The number of mature individuals is the number of individuals known, estimated or inferred to be capable of reproduction. When estimating this quantity, the following points should be borne in mind:
- Mature individuals that will never produce new recruits should not be counted (e.g. densities are too low for fertilization).
- In the case of populations or subpopulations with biased adult or breeding sex ratios, it is appropriate to use lower estimates for the number of mature individuals that take this into account.
- Where the (sub)population size fluctuates, use a lower estimate. In most cases this will be much less than the mean.
- Reproducing units within a clone should be counted as individuals, except where such units are unable to survive alone (e.g. corals).
- In the case of taxa that naturally lose all or a subset of mature individuals at some point in their life cycle, the estimate should be made at the appropriate time, when mature individuals are available for breeding.
- Re-introduced individuals must have produced viable offspring before they are counted as mature individuals.
(Source: IUCN 2010)
Observed: Information that is directly based on well-documented observations of all known individuals in the population. (Source: IUCN 2010)
Population: The term “population” is used in a specific sense in the Red List Criteria that is different to its common biological usage. Population is here defined as the total number of individuals of the taxon. For functional reasons, primarily owing to differences between life forms, population size is measured as numbers of mature individuals only. In the case of taxa obligately dependent on other taxa for all or part of their life cycles, biologically appropriate values for the host taxon should be used. (Source: IUCN 2001). The interpretation of this definition depends critically on an understanding of the definition of “mature individuals”. For application of Criteria A, C, and D, the word population usually applies to the “Canadian population”. See also “Subpopulation”.
Projected: Same as “estimated”, but the variable of interest is extrapolated in time towards the future. Projected variables require a discussion of the method of extrapolation (e.g., justification of the statistical assumptions or the population model used) as well as the extrapolation of current or potential threats into the future, including their rates of change. (Source: IUCN 2010)
Quantitative Analysis: An estimate of the extinction probability of a taxon based on known life history, habitat requirements, threats and any specified management options. Population viability analysis (PVA) is one such technique. Quantitative analyses should make full use of all relevant available data. If there is limited information, available data can be used to provide an estimate of extinction risk (for instance, estimating the impact of stochastic events on habitat). In presenting quantitative analyses, the assumptions, the data used and the uncertainty in the data or quantitative model must be documented. (Source: adapted from IUCN 2010)
Rapidly (in regards to Locations): “…..where the most serious plausible threat is habitat loss due to development, a location is an area where a single development project can rapidly (e.g., within a single generation or three years, whichever is longer) eliminate or severely reduce the population. Where the most serious plausible threat is habitat loss that occurs gradually and cumulatively via many small-scale events, such as clearance of small areas for small-holder grazing, a location can be defined by the area over which the population will be eliminated or severely reduced within a single generation or three years, whichever is longer. Where the most serious plausible threat is volcanic eruption, hurricane, tsunami, frequent flood or fire, locations may be defined by the previous or predicted extent of lava flows, storm paths, inundation, fire paths, etc. Where the most serious plausible threat is collection or harvest, then locations may be defined based on the size of jurisdictions (within which similar regulations apply) or on the level of access (e.g., ease with which collectors may reach different areas), as well as on the factors that determine how the levels of exploitation change (e.g., if collection intensity in two separate areas changes in response to the same market trends in demand, these may be counted as a single location).”(Source: IUCN Standards and Petitions Subcommittee 2019)
Reduction: A reduction is a decline in the number of mature individuals of at least the amount (%) stated under COSEWIC criterion A over the time period (years) specified, although the decline need not be continuing. A reduction should not be interpreted as part of a fluctuation unless there is reasonable evidence for this. The downward phase of a fluctuation will not normally count as a reduction. (Source: adapted from IUCN 2010)
Rescue Effect: Immigration of gametes or individuals that have a high probability of reproducing successfully, such that extirpation or decline of a Wildlife Species can be mitigated. If the potential for rescue is high, the risk of extirpation may be reduced.
Severely Fragmented: A taxon can be considered to be severely fragmented if most >50% of individuals or 50% of its total area of “occupied” (as a proxy for number of individuals) is in habitat patches that are (1) smaller than would be required to support a viable population, and (2) separated from other habitat patches by a large distance. Fragmentation must be assessed at a scale that is appropriate to biological isolation in the taxon under consideration. (Source: IUCN 2010). For complete guidance it is strongly suggested that IUCN 2010 and subsequent updates are read.
Subpopulation: As used in Criteria B and C, Subpopulations are defined as geographically or otherwise distinct groups in the population between which there is little demographic or genetic exchange (typically one successful migrant individual or gamete per year or less). Subpopulation size is measured as numbers of mature individuals only. (Source: IUCN 2001).
Suspected: Information that is based on circumstantial evidence, or on variables in different types of units. For example, evidence of qualitative habitat loss can be used to infer that there is a qualitative (continuing) decline, whereas evidence of the amount of habitat loss can be used to suspect a population reduction at a particular rate. In general, a suspected population reduction can be based on any factor related to population abundance or distribution, including the effects of (or dependence on) other taxa, so long as the relevance of these factors can be reasonably supported. (Source: IUCN 2010)