COSEWIC’s approach to assigning status is, first, to examine the Canadian status of a Wildlife Species (= designatable unit) in isolation and then, if deemed appropriate, to consider the potential for “rescue” from extra-regional subpopulations (e.g., from across an international boundary). 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 Speciescan 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 IUCN for this purpose (Gardenfors et al. 1999).
Likelihood of propagule migration
| Are there any extra-regional subpopulations 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 subpopulations 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 subpopulations 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 subpopulations 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 size of extra-regional subpopulation 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 subpopulations 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 subpopulations sinks)? |
If there is evidence that a substantial number of propagules regularly reach the region and the subpopulation still has poor survival, the regional subpopulation 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)
