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<br />r:n <br />~ <br />-9 <br />cr- <br /> <br /> <br />the preservation of wild animals than noneconomic justifications" <br />Eventually, these nations might support reintroduction pr <br />the present, they must cooperate in the establishment of such b <br />dev.eloped .na~ns, for an assumption inherent in gene bank pl'ece <br />their location m areas thought to be relatively stable and financiaU .. <br />portive. y! <br /> <br />INADEQUATE SUPPORT <br /> <br />Although many kinds of wildlife conservation efforts profit fro' <br />commonality of objective and even international orchestration, zoos <br />been viewed more as potential despoilers than as conservation educa <br />and potential wildlife preservers, sometimes with good reason. Tod <br />this attitude is changing much too slowly. Significant grants or enco <br />agement from the conservation community have been unavailable <br />propagation projects in zoos. Nor have conservationists outside ZOOS <br />tempted to establish realistic propagation objectives until, as with <br />California condor, it was nearly too late. Moreover, almost all zoos <br />municipally supported, whether by private or public funds. There is, <br />yet, no national commitment to the captive propagation of exotic speci <br />as there is for works of art through the National Endowment for <br />Arts. And there are few precedents for the exercise of international alt <br />ism py municipally oriented institutions. Even the implications of com <br />mon ownership required by national and international breeding progr <br />coordination are unclear. <br />It is clear that the development of viable captive groups for some 0 <br />the world's vanishing wildlife will require difficult choices and the aban~ <br />donment of most species in favor of a few-because of limited resources. It <br />is obvious that sufficient technologies exist for zoos to embark upon such <br />efforts, but the socio-economic mechanisms required to keep them on <br />course have not yet been developed. The reluctant skippers of these ge.' <br />netic barques and the ultimate arbiters of future evolutionary options <br />cannot help but have many misgivings, not the least of which is that by . <br />far the most attractive and most economical gene bank is the properi <br />management of animals in their native habitats. . <br /> <br />SUGGESTED READING <br /> <br />\- <br />!u <br />~ <br />~ <br />.{) <br />P <br />-:;2. <br /> <br />The literature on breeding animals in captivity is scattered and often <br />unavailable except in specialized libraries. The most complete compendi- <br />ums are various volumes of the International Zoo Yearbook, published <br />by the Zoological Society of London. Volume 17 concentrates, in part, on <br />endangered species. Another source is Breeding Eru:kzngered Species in <br />Captivity, 1975, Academic Press, London. <br /> <br />~ <br /> <br />208 <br /> <br />CHAPTER 12 <br /> <br />INBREEDING DEPRESSION <br />AND THE SURVIVAL <br />OF ZOO POPULATIONS <br /> <br />John w: Senner <br /> <br />This chapter describes a theoretical study of the genetic factors affecting <br />the survival of zoo populations. The study has two goals: to anticipate <br />the probable impact of various management strategies on the survival of <br />a captive population and to provide an estimate of the risks involved in <br />undertaking a project to maintain a particular species in captivity. To <br />achieve these goals I constructed a mathematical model of a zoo popula- <br />tion with nine parameters representing characteristics of a species or of a <br />management decision. I will summarize the essential features of this <br />model and show how variations of each of the parameters affect success <br />of a captive breeding program. (Mathematical derivation and treatment <br />may be found in the appendix.) The results will suggest that the survival <br />of small, captive populations is relatively sensitive to changes in some <br />variables (fecundity, viability, their respective genetic loads and mainte- <br />nance size) and relatively insensitive to changes in others (sex ratio, its <br />genetic load, and founder size). <br />The eventual fate of a small closed population of animals is nearly <br />always extinction. Figure 1 illustrates some of the details of the growth <br />and the inevitable decline of a zoo or reserve population founded with <br />four breeding animals and maintained at a limit of 10 animals. Heter- <br />ozygosity drops as inbreeding increases (shown as line H, where 100 per- <br />cent represents the heterozygosity level of a large population of unrelated <br />animals). As heterozygosity declines, the average survival of offspring <br />and the fecundity of parents (initially five viable offspring) declines until <br /> <br />209 <br />