Captive populations of endangered species are typically maintained effectively as single random-mating populations by translocating individuals between institutions. Genetic, disease, and cost considerations, however, suggest that this may not be the optimal management strategy. Genetic theory predicts that a pooled population derived from several small isolated populations will have greater genetic diversity, less inbreeding, and less genetic adaptation to captivity than a single large population of equivalent total size, provided there are no population extinctions. These predictions were tested using populations of Drosophila with effective size comparisons of 50 vs. 2 × 25; 100 vs. 2 × 50 vs. 4 × 25, and 500 vs. 2 × 250 vs. 4 × 100 + 2 × 50 vs. 8 × 25 + 6 × 50. Populations were maintained at the indicated sizes as separate pedigreed populations for 50 generations. The several small treatments were subsequently pooled and maintained for eight to 10 generations prior to determination of fitness and evolutionary potential. Several small populations (pooled), when compared to single large populations of equivalent total size, were found to have lower average inbreeding coefficients, significantly higher reproductive fitness under competitive conditions, similar fitness under benign captive conditions, higher genetic diversity, and equivalent evolutionary potential. Trends favored the several small (pooled) populations in all comparisons at population sizes of 50 and 100. We recommend that endangered species in captivity be maintained as several small populations, with occasional exchange of genetic material. This has genetic benefits over current management both in captivity and especially for reintroductions, as well as reducing translocation costs and risks of disease transfer.

No abstract

Captive populations of endangered species are typically maintained effectively as single random‐mating populations by translocating individuals between institutions. Genetic, disease, and cost considerations, however, suggest that this may not be the optimal management strategy. Genetic theory predicts that a pooled population derived from several small isolated populations will have greater genetic diversity, less inbreeding, and less genetic adaptation to captivity than a single large population of equivalent total size, provided there are no population extinctions. These predictions were tested using populations of Drosophila with effective size comparisons of 50 vs. 2 × 25; 100 vs. 2 × 50 vs. 4 × 25, and 500 vs. 2 × 250 vs. 4 × 100 + 2 × 50 vs. 8 × 25 + 6 × 50. Populations were maintained at the indicated sizes as separate pedigreed populations for 50 generations. The several small treatments were subsequently pooled and maintained for eight to 10 generations prior to determination of fitness and evolutionary potential. Several small populations (pooled), when compared to single large populations of equivalent total size, were found to have lower average inbreeding coefficients, significantly higher reproductive fitness under competitive conditions, similar fitness under benign captive conditions, higher genetic diversity, and equivalent evolutionary potential. Trends favored the several small (pooled) populations in all comparisons at population sizes of 50 and 100. We recommend that endangered species in captivity be maintained as several small populations, with occasional exchange of genetic material. This has genetic benefits over current management both in captivity and especially for reintroductions, as well as reducing translocation costs and risks of disease transfer. Zoo Biol 17:467–480, 1998. © 1998 Wiley‐Liss, Inc.

No abstract

Many natural populations fluctuate widely in population size. This is predicted to reduce effective population size, genetic variation, and reproductive fitness, and to increase inbreeding. The effects of fluctuating population size were examined in small populations of Drosophila melanogaster of the same average size, but maintained using either fluctuating (FPS) or equal (EPS) population sizes. FPS lines were maintained using seven pairs and one pair in alternate generations, and EPS lines with four pairs per generation. Ten replicates of each treatment were maintained. After eight generations, FPS had a higher inbreeding coefficient than EPS (0.60 vs. 0.38), a lower average allozyme heterozygosity (0.068 vs. 0.131), and a much lower relative fitness (0.03 vs. 0.25). Estimates of effective population sizes for FPS and EPS were 3.8 and 7.9 from pedigree inbreeding, and 4.9 vs. 7.1 from changes in average heterozygosities, as compared to theoretical expectations of 3.3 vs. 8.0. Results were generally in accordance with theoretical predictions. Management strategies for populations of rare and endangered species should aim to minimize population fluctuations over generations.