Table 2.
Likely benefits (+) and costs (−) of different types of genetic mixing strategies
| Genetic mixing strategy | Source population size | History of recipient population size | ||
|---|---|---|---|---|
| Persistently small | Small, recent decline | Small in past but potential to expand a | ||
| Immediate effects (F1, F2) | ||||
| Genetic rescue (overcoming genetic load by masking deleterious alleles) | Small | + → ++ | + → ++ b | + → +++ |
| Large | + → ++ | + → ++ b | + → +++ | |
| Evolutionary rescue (through increasing connectedness) | Small c | + | + | + |
| Large | ++ | + | ++ | |
| Longer‐term effects (F3+) | ||||
| Genetic rescue (continued accumulation of deleterious alleles) | Small | ‐‐ | ‐‐ | = d |
| Large | ‐‐‐ | ‐‐‐ | = d | |
| Evolutionary rescue (through increasing connectedness) | Small | = | = | + |
| Large | + | + | +++ | |
Benefits can be immediate (F1, F2 stage) or longer term (F3+) and will depend on the source population(s) available for genetic material and the population size history of the recipient population. = represents same effect as in immediate effects. The advantages and costs are separated into those associated with genetic versus evolutionary rescue as defined in Table 1.
a
Assumes population continues to expand as extrinsic threats are mitigated.
b
Depends on level of inbreeding during decline.
c
Depends on some beneficial alleles being introduced from the small source population.
d
Assumes effective purging of deleterious alleles (decrease in genetic load).