COSEWIC wildlife species assessment: guidelines for modifications based on rescue effect
Table 3. Guidelines for modifying status assessment based on rescue effect
Committee on the Status of Endangered Wildlife in Canada's (COSEWIC) approach to assigning status is, first, to examine the Canadian status of a wildlife species or other Designatable Unit below the species level in isolation and then, if deemed appropriate, to consider the potential for "rescue" from extra-regional subpopulations (e.g., from across an international boundary or from another Designatable Unit within Canada). The rescue effect is the immigration of gametes or individuals that have a high probability of reproducing successfully, such that extirpation or decline of a wildlife species, or some other Designatable Unit, can be mitigated. If the potential for rescue is high, the risk of extirpation may be reduced, and the status may be downgraded. COSEWIC addresses this by applying the following guidelines developed by International Union for Conservation of Nature (IUCN) for this purpose (Gardenfors et al. 1999).
Likelihood of propagule migration
Are there any extra-regional populations within a distance from which propagules could reach the region? Are there any effective barriers preventing dispersal to and from extra-regional subpopulations? Is the wildlife species capable of long-distance dispersal? Is it known to do so?
If there are no extra-regional populations or propagules are not able to disperse to the region, the regional subpopulation behaves as an endemic and the status category should be left unchanged.
Evidence for the existence of local adaptations
Are there any known differences in local adaptation between regional and extra-regional subpopulations, i.e. is it probable that individuals from extra-regional populations are adapted to survive within the region?
If it is unlikely that individuals from extra-regional subpopulations would be able to survive within the region, the status category should be left unchanged.
Availability of suitable habitat
Are current conditions of habitats and/or other environmental (including climatological) requirements of the taxon in the region such that immigrating propagules are able to successfully establish themselves (i.e. are there inhabitable patches), or has the taxon disappeared from the region because conditions were not favourable?
If there is not enough suitable habitat and current conservation measures are not leading to an improvement of the habitat within a foreseeable future, immigration from outside the region will not decrease extinction risk and the status category should be left unchanged.
Status of extra-regional subpopulations
How abundant is the taxon in neighbouring regions? Are the populations there stable, increasing or decreasing? Are there any important threats to those subpopulations? Is it probable that they produce an appreciable number of emigrants, and will continue to do so for the forseeable future?
If the taxon is more or less common outside the region and there are no signs of subpopulation decline, and if the taxon is capable of dispersing to the region and there is (or soon will be) available habitat, downgrading the category is appropriate. If the population size of extra-regional subpopulations is declining, the 'rescue effect' is less likely to occur, hence downgrading the status category may not be appropriate.
Degree of dependence on extra-regional sources
Are extant regional populations self-sustaining (i.e. have they shown a positive reproductive rate over the years) or are they dependent on immigration for long-term survival (i.e. are the regional populations sinks)?
If there is evidence that a substantial number of propagules regularly reach the region and the population still has a poor survival, the regional population may be a sink. If so, and there are indications that the immigration will soon cease, upgrading the status category may be appropriate.
Figure 1. Schematic Guidelines for Applying the Rescue Effect (adapted from Gardenfors et al 1999)