SUPPORTIVE BREEDING AND VARIANCE EFFECTIVE POPULATION-SIZE

The practice of supporting weak, wild populations through release of i ndividuals bred in captivity is becoming an increasingly important con servation measure. A frequently recommended form of such breeding-rele ase activity refers to supportive breeding: a fraction of the target p opulation is brought into captivity for reproduction, and the resultin g progeny are released to mix with the wild segment of The Population. We derived an expression for the variance effective size of a populat ion managed through supportive breeding and discuss its relationship t o previously published equations that are based on the assumption of r andom mating. We show that the effect of supportive breeding may be qu ite different on the inbreeding and the variance effective sizes. Wher eas supportive breeding always results in a reduction of the inbreedin g effective number the variance effective number may either decrease i ncrease, or remain unchanged. We discuss these observations in relatio n to conservation management and suggest some general guidelines for s upportive breeding situations. Our recommendations include making a di stinction between inbreeding and variance effective numbers; taking pa rticular care when dealing with organisms with high reproductive poten tial; assuring that the amount of drift be no larger than it would be without supportive breeding; and focusing primarily on the variance ef fective size of a population-that is, on the effective number directly related to the rate of loss of gene diversity.