Thomas Foose

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13Table 3. Status of black rhinos in Africa.% of total1987 rhino1980 1984 1987 populationTanzania 3 795 3130 270 7%C.A.R. 3 000 170 10? 0.2%Zambia 2 750 1650 110 3%Kenya 1 500 550 520 14%Zimbabwe 1 400 1 680 1 760 46%South Africa 630 640 580 15%Namibia 300 400 470 12%Sudan 300 100 3 —Somalia 300 90 ? —Angola 300 90 ? —Mocambique 250 130 ? —Cameroon 110 110 25?  0.7%Malawi 40 20 25  0.7%Rwanda 30 15 15 0.4%Botswana 30 10 10 0.2%Ethiopia 20 10 ? —Chad 25 5 5? —Uganda 5 — — —TOTAL 14 785 8 800 3 800tion strategy, and has been producing annually-revised ac-tion plans for the conservation of rhinos and elephants.In discussing the draft strategy, an emphasis that emergedfrom the workshop was the need for interactive managementof wild and captive populations in order to maintain geneticvariability. However, it was agreed that ex situ breeding pro-grammes should avoid mixing rhinos from different regionsof Africa in order not to destroy probable adaptations to par-ticular environmental factors in these ecologically divergentregions. The numbers of remaining rhinos in the four regionalgroups that were identified for separate genetic managementare shown in Table 4.Table 4. Estimated numbers of black rhinos in regional units.Regional conservation unit NumberSouthwestern 500Southern/Central 2 600Eastern 600Northern/Western 50STATUS  OF BLACK RHINOS lN CAPTIVITYTables 5 and 6 summarize the current status of black andother rhinos in captivity at the time of the workshop. Figuresdiffer slightly from those used by Lynn Maguire and RobertLacy in their analyses in these proceedings—owing to differ-ent sources of information—but not to a significant extent.There appears to be captive habitat in zoos for about 700-800 rhinos, using current collections as a crude estimate.Black rhinos are currently allocated about 20% of thesespaces, while white rhinos occupy a disproportionate 60%(owing largely to their ready availability from South Africa).The black rhino population in North America, now undermanagement of the AAZPA Species Survival Plan (SSP),has been increasing slowly over the last five years at a rateof about 2% per annum (Table 7). Birth rates have been quiteencouraging (in contrast to the white rhinos, which have notreproduced well as a probable consequence of this species’inclination to breed better in group situations than when keptTable 5. Current populations of rhino in captivity. Sourcesare AAZPA Species Survival Plans (SSP), the internationalSpecies Inventory System (ISIS), International Zoo Yearbook(IZY), and the International Studbooks for African Rhinos (ZooBerlin) and Indian Rhinos (Basel Zoo).Species North America WorldIZY StudbookBlack 30/38 =68 68/80 = 148 82/98 =180White  Southern 70/93 = 163 177/215 = 392 313/357 = 670  Northern 1/0 = 1 6/5 = 1 6/5 = 1Indian 16/12 = 28 44/35 = 79 44/35 = 79Sumatran 0 3/6 = 9 3/6 = 9Javan 0 0 0TOTAL 117/143 = 260 298/341 = 639 448/501 = 949Table 6. Estimated captive capacity or habitat (space andresources) for rhinos in the world’s zoos.Species North America WorldBlack 125 200-250White 100 (+25?) 200-250Indian 75 150Sumatran 75 150Javan ? ?TOTAL 375-400 700-800Table 7. Performance of North American zoos with blackrhinos, 1982-1986.Year Births Deaths Dispersed Imported1982 1/3 2/2 1/11983 2/2 0/1 2/0*19841985 2/5 3/2 0/11986 4/3 3/3TOTAL 9/13 8/8 0/1 3/1*Captive born in Japanas pairs). Death rates in black rhinos have been high, largelybecause of the haemolytic anaemia syndrome discussed laterin these proceedings. intensive research to resolve this prob-lem is in progress and some hopeful insights have alreadybeen obtained, especially in terms of possible vitamin E de-ficiencies.LONG-TERM MANAGEMENT OF SMALL RHINOPOPULATIONSThomas Foose (American Association of Zoological Parksand Aquariums).Overview of concernsAs discussed by Lynn Maguire in the preceding session, andelaborated by Robert Lacy in the following presentation, thetrend towards very small and fragmented populations in thewild (i.e. towards the situation of rhinos to captivity) makesthese populations vulnerable to extinction for genetic anddemographic reasons. Small populations lose genetic diver-sity rapidly at the population level (Fig. 3) as well as at theindividual level. At the population level, genetic diversity Is14graphic winter”’ (the period extending for the next 200 to 500years, during which human population growth and develop-ment will continue and intensify disruption of natural sys-tems). However, the winter may vary on a species-by-speciesand area-by-area basis.Biological characteristics that influence MVP sizes includethe following:1.) The generation time of the species. Genetic diversity islost generation by generation, not year by year. Thus somegiven period of time, e.g. 200 years, represents more gen-erations, hence more opportunity to lose diversity, for a spe-cies like a galago than it does for a species like a rhino.2.) The Ne/N ratio of the population. Loss of diversity doesnot depend simply on total population size, but rather on thegenetically effective size (which reflects how the animals areactually reproducing to transmit genes to the next genera-tion). Very generally, the genetically effective size of a popu-lation depends on:— the number of animals actually reproducing;— the sex ratio of the reproducing animals;— the relative lifetime number of offspring (i.e. family sizeof animals in the population).Since Ne is normally less (often much less) than the censusnumber (N), MVP’s must be larger than the population sizesprescribed by genetic calculations since these prescriptionsare always in terms of Ne.3.) The number of founders that establish a population.Founders are animals out of a wild population that are usedto establish a captive or a new wild population (or augment arecovering wild population). Conversely, they could be ani-mals from captivity that are used to re-establish a species inthe wild. in general, the larger the number of founders, thesmaller the MVP needed for some genetic objectives. How-ever, there is a point of diminishing returns so that usually20-30 founders may be adequate.4.) The reproductive rate or recovery potential of the popula-tion. Much genetic diversity can be lost either as the popula-tion grows from its foundation size to carrying capacity orduring recovery from periodic reductions. in general, thehigher the reproductive rate and hence growth or recoveryto carrying capacity, the less genetic diversity is lost.5.) The degree of subdivision or fragmentation in the popu-lation. If a species is fragmented into a number of subdivi-sions which are Isolated from one another, animals may notbe able to move around for breeding and hence exchange ofgenetic material. Such situations can cause loss of geneticdiversity. On the other hand some subdivision may assistretention of some kinds of genetic diversity. The importantpoint is that conservationists must analyze the genetic proc-esses in the species under consideration and develop anappropriate management plan that may include artificialmovement or manipulation of animals, to synthesize manyseparate smaller populations into a so-called metapopulationcapable of greater long-term viability.Clearly, there is no single MVP figure that will apply to allspecies or to all situations for any given species. Rather,MVP’s will vary depending on the objectives of the programand the circumstances of the species. Detailed explanationand expansion of the MVP concept are provided by Gilpinand Soule (1986), Shaffer (1987) and Soule (1987). The proc-ess of determining the size of a population that is required toachieve some level of genetic and demographic security hascome to be known as population viability analysis (PVA).Figure 3. The decline of genetic diversity (measured as av-erage heterozygosity in the total population) over 50 gen-erations for various effective population sizes (Ne), possiblefor a total population (N) of 250.vital to permit adaptation to continually changing environ-ments. At the individual level, genetic diversity is required tomaintain the “vigour” of the animals; loss of diversity in indi-viduals is known as inbreeding and a consequent decline insurvival and fecundity rates is inbreeding depression.Conservation biologists have suggested that genetically ef-fective population sizes (Ne’s) of 50 or more are necessaryfor the shorter term (5-10 generations) mainly to counteractinbreeding depression, while Ne’s of 100-500 or even moremay be necessary over the longer term to maintain adapt-ability. The vulnerability of small populations to demographicrisks (disease epidemics, natural disasters, uneven sex ra-tios, etc.) imposes a further minimum limit to desirable popu-lation size: conservation biology—models suggest thatpopulations must be no smaller than 25-50 total individualsto survive unpredictable (stochastic) demographic risks.To preserve a species against these genetic and demographicrisks, it is therefore necessary to establish some minimumviable population size (MVP). The actual MVP that is recom-mended will depend on the defined objectives for the spe-cies at risk as well as the biological characteristics of thatspecies (Soule et al., 1986). The major relevant concernsare as follows.1.) The probability of survival of the population. No finite popu-lation size will completely insure a species against stochasticextinction, but It is sometimes possible to specify populationsizes that will insure some probability of survival (e.g. 50%;90%). For some given period of time, the higher the stipu-lated probability of survival, the larger the MVP required. 2.)The level of genetic diversity to be preserved. Obviously, thetop objective would be to retain all the genetic diversity. How-ever, with the restricted populations possible (In the wild orcaptivity), something less than all may have to be acceptedfor some period of time. Preserving rarer alleles (i.e. specificvarieties of genes) will require larger MVP’s than merelymaintaining average heterozygosity (some variation of any,non-specific kinds). Preserving 95% of average heterozy-gosity will require an MVP twice as large as’90% will. Popu-lation geneticists are not certain how much genetic diversityis enough but levels of at least 90% of average heterozygos-ity have been strongly suggested.3.) How long this level of genetic diversity must be preserved.The optimal answer is indefinitely, i.e. the species could thencontinue to evolve as environments change. But again, theremay have to be compromises. Hopefully, intensive pro-grammes will be needed only through the present ““demo-15PVA attempts for black rhinosTable 8 represents some initial attempts at prescribing MVP’sfor both wild and captive black rhinos. These analyses wereperformed using microcomputer software developed by JonBallou of the National Zoological Park in Washington, DC,and are extremely tentative. To refine the PVA models andtheir data inputs, there needs to be more collaboration be-tween conservation biologists and field managers of blackrhinos. However, since there is an urgent need for manage-ment guidelines, a number of preliminary recommendationsbased on these rough analyses have been generated forconsideration.An Ne = 500 is proposed for each regional conservation unitof black rhinos. This represents a number sufficiently high toensure maintenance of genetic diversity (e.g. 90% averageheterozygosity for 50 rhino generations) and demographicsecurity.An Ne/N ratio of 0.25 to 0.5 is proposed as a further opera-tional guideline in formulating conservation strategies forblack rhinos. With management, especially in captivity, it maybe possible to improve this ratio. Simple arithmetic indicatesthat to achieve an Ne = 500 with a worst case situation ofNe/N = 0.25, an MVP of 2 000 would be required for eachconservation unit of rhinos.Since black rhino populations will be fragmented and re-sources for conservation limited, it also seems advisable tosuggest a size for individual populations of black rhinos withineach conservation unit. The number roughly indicated byanalyses so far is 100-200. This guideline does not dictatethat populations smaller than this size are worthless but thatthey should probably receive lower priority for conservationefforts than larger ones. Realistic cost-benefit analyses needto be performed on each of the rhino populations of limitedviability to determine if intensive and interactive managementin feasible in both logistic and economic terms, it should beemphasized that the figure suggested here applies not toactual current population, but to potential size of the popula-tion in the given area if rhinos can be adequately protectedto reach carrying capacity.Finally, it should be realized that individual populations of100-200 are not likely to be genetically and demographicallyviable by themselves over periods of time in the order ofcenturies. There will need to be interchange between sepa-rate populations to create the so-called “metapopulations”for each conservation unit. Where natural migration is notpossible between separate populations, management willhave to artificially move animals for genetic and demographicreasons as suggested by appropriate PVA analyses.Because of the limited space and resources available in exsitu facilities, MVP’s may have to be, and probably can be,even more precisely defined for captive than for wildpopulations. An objective for captive propagation of preserv-ing 90% of average heterozygosity for 200 years is a com-mon recommendation of conservation biologists consideringprinciples of population genetics (i.e. inbreeding) and demog-raphy as well as the likely period of time that human pres-sures will be most intense on wildlife. To achieve objectivesof preserving a significant fraction (90%) of the wild genepool for 200 or so years, a number of combinations of ulti-mate carrying capacity, initial founder numbers, and popula-tion growth rates will produce the desired results (asdemonstrated in Table 8).As a result of these preliminary analyses, the zoo commu-nity is proposing to develop captive populations of 150 eachTable 8. Minimum viable populations required to preserve90% average heterozygosity for various periods, in severaldemographic situations.A. GENERATION TIME = 15 YEARS.POPULATION GROWTH RATE = 1.03/YEARNe/N Ratio = 0.5YEARS75 150 225 300 450 600 750EFFECTIVE 10 – – – – – – –NUMBER 20 62 131 236 367 603 8911 134OF 25 50 121 189 273 459 641 832FOUNDERS 30 50 103 170 241 393 551 71250 50 100 156 203 319 439 56175 50 100 150 193 297 404 513100 50 100 150 193 289 392 495B. GENERATION TIME = 15 YEARS. POPULATIONGROWTH RATE = 1.06/YEARNe/N Ratio = 0.5YEARS75 150 225 300 450 600 750EFFECTIVE 10 115 292 534 786 1310 1842 2384NUMBER 20 50 115 187 261 414 568 727OF 25 50 106 170 235 369 505 642FOUNDERS 30 50 102 160 221 345 471 59850 50 100 147 200 308 417 52775 50 100 150 193 293 397 501100 50 100 150 193 289 389 489C. GENERATION TIME = 15 YEARS.POPULATION GROWTH RATE = 1.06/YEARNe/N Ratio = 0.25 YEARS75 150 225 300 450 600 75010 230 583 1069 1573 2621 3685 4769EFFECTIVE 20 101 231 374 522 829 1136 1451NUMBER 25 100 212 339 470 737 1010 1284OF 30 100 204 320 442 689 942 1195FOUNDERS 50 100 200 295 400 615 835 105475 100 200 295 386 589 794 1001100 100 200 295 386 579 778 997for at least two of the conservation units of black rhinos; theNorth American AAZPA SSP will attempt captive populationsof 75 for each of these two units. The constraints imposedby the biological characteristics of the species will prescribea critical minimum for the number of founders (i.e. animalsout of the wild) that will be needed to establish the captivepopulation. For black rhinos, 20-25 effective founders for eachconservation unit maintained seems desirable.FURTHER GENETIC AND DEMOGRAPHICANALYSES OF SMALL RHINO POPULATIONSSummary of presentation by Robert Lacy(Chicago Zoological Society)This work is quite preliminary, providing initial insights andpossible directions for future analysis, not definite conclu-sions or recommendations about rhino populations. The

Long-term management of small rhino populations

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Long-term management of small rhino populations

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