V.E. Sokolov and V.N. Orlov
The Asian wild horse, known as Equus przewalskii and named after N.M. Przewalski, explorer of Central Asia, earlier populated a vast territory of Asian steppes, stretching from the Kazakh area to the piedmonts of Tien Shan and the Mongolian Altai.
Yet in the 18th century the wild horse was usual in the steppes of the Kazakh area, Mongolia and Dauria. Already in 1637 a wild mare was caught in the territory of the modern Choybalsan Aimak, in the interfluvial area of the Onon and Kerulen rivers; it was later given as a gift to the Manchurian Emperor. In accordance with the information provided by last century travellers the wild horses ranged in the vast area of Dzungaria, from the piedmont areas of the Mongol Altai in the north to the Tien Shan in the south, from longitude 86°E in the west to longitude 95°E in the east. The reports said that the wild horse populated the areas even more to the east, the southern piedmont areas of the Mongol Altai (longitude 105°E) and the Shargyn Gobi to the north from the Mongol Altai.
In the 1940s big herds of the wild horse were still observed in the Dzungar Gobi, in the territory of Mongolia. Nevertheless, in the late 1940s the wild horses almost fully disappeared in Mongolia. Thus, only one expedition out of the four working in that region in the 1950s was lucky to see a lone stallion and one band was seen by the arats (local residents) in the winter of 1956. In the 1960s, only two expeditions out of the eight visiting that area saw the wild horses; 5 horses in June 1967, the same number was seen in May 1968; both times in the vicinity of solontchak Takhiin-Us. Three reported sightings of the wild horses by the local residents are registered in the 1960s as well (in the winter of 1969, 1964 and in the summer of 1969). Since that time neither members of the expeditions, nor the local people, have seen any bands of the wild horses. We thoroughly studied the Dzungar Gobi in the territory of Mongolia in the summer of 1976 and 1977, in the summer and winter of 1979, and no traces of the wild horse were found. Having enquired with the local residents we came to a conclusion that the Przewalski horse no longer exists in the territory of Mongolia. It is unlikely that the wild horse is still preserved in China. The piedmont areas of the Tien Shan and of the Baitag Bogdo range are more developed and more populated than the Mongol part of Dzungaria. A well-known geographer E.M. Mourzayev did not see the wild horse and could not obtain any information from the local residents during his travels in Sinkiang in 1956–1959, though he travelled in the places where the sightings of the wild horse were frequent in the last century. The expedition of the Peking zoo that worked in Sinkiang in 1955/57 did not meet the Przewalski horse either.
The firearms that became available to the local residents and the shooting of the animals in the 1940s, severe winters and the intensive economic use of grazing lands and watering places are considered to be the principal factors responsible for the rapid extinction of the Przewalski horse. All that is true. Nevertheles, Kulan, another perissodactyl species, managed to secure its high numbers under the same conditions. Przewalski horse extinction, as we see it, can be explained in the first place by the fact that they were ousted by man to the desert from the optimal habitat, that is the Stipa-Artemisia and other types of arid steppes. Contrary to Kulan, the wild horse can live in steppes and semi-deserts but not in deserts. Ousted by man to the desert, the wild horse was doomed to death. Due to that reason, the wild horses disappeared in the Kazakh area one hundred years earlier than Kulans. Within the boundaries of the restored habitat of the Przewalski horse in Dzungaria, the Stipa-Artemisia arid steppes occupy a relatively small territory, namely the northern piedmont areas of the Tien Shan and the narrow strips along the southern piedmonts of the Mongol Altai, piedmonts and low mountains of the Baitag-Bogdo and Takhin-Shara-Nuru chains, stretched longitudinally. These three strips of arid steppes are alternated by the vast areas of Halozylon and Salsola deserts. Consequently, the wild horses were distributed sporadically within that restored vast habitat, and their total number was not great.
Yet in the 19th century, the wild horses were ousted from the piedmonts of the Tien Shan to the desert areas. Typical samples of the Przewalski horse and the horse obtained by the Grum-Grzimailo brothers were shot in the sand area and the crushed stone desert to the north from the Tien Shan piedmonts. It is significant that the last sightings of the wild horse in Mongolia were registered in the Haloxylon desert, in the vicinity of Takhiin-Us solontchak.
At present, the representatives of this species can be seen only in the zoos and reserves of the world. The total captive population of the wild horse derives from 12 wild horses, imported from Dzungaria into Europe at different times and one domestic mare. Totally, 53 wild foals were imported. Since the horses were small in number they were distributed among the zoos of Europe and North America by pairs or by one, that later resulted in the formation of isolated inbred groups. It is not accidental that only three zoos (New York, Woburn, Askania Nova) managed to ensure stable reproduction. In total, a little over one hundred foals were born before the Second World War. After its boom, the reproduction of the wild horse in captivity started to decline and by the late 1930s almost all the captive population had become extinct. The horses that were later used for breeding remained only in the Prague and Hellabrunn Zoos. That was an unsuccessful end to the first stage of Przewalski horse captive reproduction.
Among the reasons that led to the extinction of the wild horses in the zoos one can mention the unacceptability of the urban zoo environment for the wild horse, contradiction between the commercial objectives and those of preservation of a diverse gene pool, as well as the Second World War during which many zoos were destroyed. After the end of the war the second stage of the wild horse reproduction began and it was more successful. The horses that currently populate more than 80 zoos of the world established a great number of new genetic lines and branches. The world population of the wild horse began to grow steadily only after 1950 and by 1 January 1984 it had reached 552 head that are distributed among many zoos; as mentioned above, the majority of zoos keep one or a pair of horses. Foals are born every year in only 20–30 centres out of a total of 80, and 15–17 zoos have an increase of only one new foal annually. Taking into account mortality (6–8%) the total annual growth accounts for 8–10%. Within the total population the purebreds that have no blood of the domestic horse account for only 30%. The mares account for 60–70% of that group, and only about 20% of them participate in reproduction and produce the offspring. Total number of newborn foals per one year is 70–80 and 17–26% of them die. Among the two-year-olds 42% die and only 3% of them reach the age of 30 (Volf 1984). The changes in gene frequencies of the protein polymorphic systems, in enzymes and the blood groups are observed within the isolated populations of the Przewalski horse.
Descendants lose certain alleles which results in the decrease of the protein and blood enzyme polymorphic characteristics of each first or second generation by 10%, and accounts for 50–70% in the modern population of the wild horse. The inbreeding coefficient increases by 0.03–0.06% with each subsequent generation. When this coefficient amounts to 0.5%, infertility and non-viability are observed. The efficient number of horses even in large zoos does not exceed 4 head. And the total horse number in those zoos reaches 15–20!
All this points to the fact that only one stallion is used for breeding in these zoos. Not a single zoo in the world uses its capabilities to the full extent. As a result, homozygosity is increasing and the gene pool is being depleted in the isolated groups of horses, and it affects their reproduction abilities and viability.
The Przewalski horses in captivity are subject to behavioural morphological changes. The stallions that are not involved in competition do not obtain the typical agonistic behaviour patterns that can change their social ranking and would eventually allow them to take over mares. They are not able to take possession over mares and to fix their reproductive success. Due to the absence of physical loads and the decreased consumption of feeds the horses that are in captivity for a long period have less teeth and the face bones are poorly developed; the skeletal bones, not having sufficient loads, become somewhat shorter and more massive. The horses gain additional weight and their overall exterior is shifting from gait-type to that typical for walking. Already they are not capable of covering long distances as their ancestors in nature did.
Overall, it can be said that this species has lost a number of features that allowed the wild horse in the past to withstand the severe environmental conditions of Central Asia. This refers both to the phenotype and genotype features, taking into account the growing homozygosity and the loss of gene pool variability. Since the factors that cause such phenomena are still existing these processes continue to develop and the captive evolution of the species continues. That is why there is a possibility to have another species under the name of Equus przewalskii Pol. tomorrow! As we see it, the perspectives for the future survival of this species in captivity, under conditions totally different from the natural environment, are not very bright. In the future we will face further domestication and the loss of variability of the gene pool that is in full contradiction with the objectives of preserving that species. The world scientists display permanent concern over the fate of Equus przewalskii as a species. The resolutions of all international symposia on the survival of Equus przewalskii stress that captive reproduction does not guarantee the preservation of the diverse gene pool. The most radical measure of saving that species will be the wild horse introduction into the natural biotopes and creation of a big population in nature. The return of the horses to the natural steppe biotopes will not only ensure the preservation of their gene pool, genetic type, and the follow-up natural evolution, but will enrich the natural communities and will become a model for the preservation of other types that will give a powerful impetus to world environmental activities.
It is necessary to find out what number of horses will be sufficient for the preservation of the species gene pool. We believe that the natural population of the wild horse should be no less than 300–500. It is this number that provides a guarantee for the preservation of genetic variability for quite a long period. The total wild population should be 1–2000. It is essential to reach this level during the first decade, by the beginning of reproduction of 3–4 generations of horses. Under favourable conditions such a level can be reached if 30–50 horses from the zoos are reintroduced into nature during the first years and the same number is introduced for the next 3–5 years.
The horses to be introduced will be provided free of charge by the zoos of some European countries, of North America and the USSR. By 1 January 1985 the population of Equus przewalskii in the zoos of the Soviet Union was 100 (47 females, 53 males). About 10% of that population can be allocated for introduction in Mongolia.
In recent years the USSR Academy of Sciences and the State Committee for Science and Technology of Mongolia have undertaken a number of steps aimed at preparation for the introduction of Equus przewalskii into nature. Thus, the USSR-Mongolian biological expedition studied various regions of Mongolia and a number of areas for the future reintroduction was selected. On the suggestion of the expedition the Council of Ministers of the Mongolian People's Republic passed a decision on reacclimatization in that country of the Takhi wild horse.
The selection of areas in the MPR suitable for the wild horse reintroduction, conducting their zoological and geographical survey, and designing a Horse Reintroduction Centre in the Bogdo-Ula natural reserve in the vicinity of Ulan Bator can be assessed as the practical results of that activity.
It is very positive that such authoritative international organizations as UNEP, FAO, IUCN and others, as well as the national institutions in the countries where the Przewalski horse is managed, are ready to participate in such a programme.
On the threshold of another stage of the Przewalski horse survival programme the Soviet scientists are presenting their views on the processes of Equus przewalskii introduction into nature.
It is necessary to organize a step-by-step shipping of the wild horses from the zoos into nature. During the first stage the horses will go through an initial adaptation in semi-reserves of the USSR. During stage two after adaptation in the USSR, the horses will be moved to the semi-reserves in Mongolia. They will adapt there to the even more severe natural conditions of Central Asia, and then they will be transported to the places of release which will be the third step of introduction.
At the first stage of this process that will be taking place in the steppe area of the European part of the Soviet Union and in the Kazakh republic, the following objectives are outlined:
Initial acclimatization of zoo horses in semi-reserves in the more severe environment of Eastern Europe and the Kazakh republic which stipulates both climatic and social adaptation. In the conditions of competition adequate behavioural patterns will be formed that will assist in their survival in the conditions of the natural bioptopes and to their on-going reproduction.
Production of offspring and horse breeding.
Preparations for introduction, including the formation of groups, selection of the best groups for introduction.
Monitoring and study of adaptation processes, formation of the desirable behaviour patterns.
In order to realize the above mentioned objectives, a semi-reserve should meet the following requirements:
Availability of large fenced steppe plots with a size of at least 5–7000 hectares.
Availability of administrative and management staff to provide services.
The presence of research personnel, veterinarians, etc. is essential.
Locality in the steppe area, in the vicinity of highways and railroads.
The best place to set up such a semi-reserve will be “Askania Nova” steppe reserve, as we see it. It is situated within the boundaries of the historic range of the East European Tarpan that became extinct in the last century. The vast plots of virgin feather grass with sheep, a fescue steppe that has been conserved since the last century, have remained intact. The reserve boasts good traditions in preservation and breeding of the Przewalski horse and other rare species of mammals and birds. It has a proper geographical location in the steppe zone of the European part of the USSR. The climate is mild but severe enough for the animals from the zoos of West Europe and North America. The average winter air temperature is -3°C, sometimes as low as -20°C. The average summer temperature is +20°C, up to +40°C.
The second semi-reserve for the first stage of the programme may be one of the zoos in the Kasakh republic, e.g. Karaganda zoo in the Eastern part of the Kazakh republic, or Chimkent zoo in the South of the republic. Both are situated within the boundaries of the historic range of Equus przewalskii, in the steppe zone. Both zoos have a vast enough territory to set up such a semi-reserve. The climate in those areas is even more severe than in Askania. The winter air temperature reaches -25–30°C.
Besides assisting in the realization of introduction, such semi-reserves will be important for the preservation of the zoo horse populations.
Thus, the horses that go through the initial adaptation in semi-reserves can be shipped back to the zoos that provided them. The breeding activities may be more efficiently carried out in semi-reserves, as well as horse exchanges, holding, and formation of groups.
In order to fulfil the objectives of the second stage it is essential to set up semi-reserves for management and adaptation in the Mongolian People's Republic. The objectives of this stage are as follows:
Holding and adaptation of horses provided by semi-reserves of Askania Nova and the Kazakh Republic in the climatic conditions of the region.
Formation of stable social groups and creation of adequate behavioural patterns that assist horse survival. These include the skill of getting food from under the snow cover with the help of hooves in the winter, self protection from midges, wind, etc.
Reproduction, production of offspring, their adaptation, “education”, etc.
Monitoring of the introduction and adaptation processes.
Providing aid to the horses that failed to withstand the severe environmental conditions; providing them with veterinary aid, additional feeding.
Preparation of horse groups to release into nature: formation of groups.
The requirements of the places for such semi-reserves are the same as in the first stage. The additional requirement is to locate them in the zone of the Mongolian steppes of the mountain steppes of the semi-arid zone. The possible places for setting up such semi-reserves are the Eastern Khangai, Mongolian Altai near the northern border of the Gobi reserve, the Kerulen river valley and the surroundings of Ulan Bator.
It should be stressed that contrary to the steppes of Western Europe and the Kazakh area with steppe associations of plants, the Mongol steppes are poorer. Therefore, the wild horses have to be additionally fed on almost a year-round basis both in semi-reserves and in the places of release. That is why the semi-reserves should be supplied with a large stock of rough fodder.
The final choice of the place for a semi-reserve can be made in agreement with the Mongolian side. Nevertheless, we shall give a brief description of some above mentioned regions.
One of the oldest Mongolian reserves of Bogdo Ula is situated in the vicinity of Ulan Bator. The total territory of the reserve is 54 200 hectares and it is located at an altitude of 2256 m above sea level. The highest parts of the Bogdo Ula mountains are covered with Cedrus forests and partially by alpine meadows. The border-line parts of the mountains and slopes are covered with steppes: Sedge, Poa and motley grass steppe on the northern macro-slope; wheat grass, motley grass, and soddy and grassy areas on the southern macro-slope. Petrophyte and Festuca motley grass are observed on the eastern and western macro-slopes. The total area of steppes in the reserve is 33 600 hectares. In the winter the air temperature may reach -20–35°C, averaging -10°C. The temperature in the summer reaches +22°C, the average figure being +5.6°. The snow cover is 3–5 cm on average, up to 14 cm and annual precipitation is 250–280 mm.
The area of Eastern Khangai that is suitable for the location of a semi-reserve is situated 295 km to the southwest from Ulan Bator. As compared with Ulan Bator the winter here is milder and with little snow. The summer air temperature is somewhat higher. The area is a plain with occasional mountains and cone-shaped hills up to 1300–1500 m high. In ravines groves of thickset elm trees, various brushes and well-developed steppe vegetation are observed. The sandy loam soils prevail in these areas. The steppes are mostly covered with wheat grass, sagebrush, and Caragana, their production being 300–400 kg of dry matter per hectare. Some water resources in the southern slopes dry up in the summer; nevertheless there are several rivers that supply the surrounding biotas with water on a year-round basis.
In some of these regions, especially those situated in the steppe zone in the south, the horses may be released into nature upon their sufficient adaptation.
During the third stage of the programme the horses are held in the fenced plot near the release spot, later they are released by groups into nature. Preliminary holding is necessary to give the horses from semi-reserves an opportunity to get acquainted with a particular territory.
The objectives advanced for this stage are as follows:
To hold the groups of horses for a season or a year, to ensure their adaptation in the release places.
To release the horses by groups into the wild. Some animals, preferably related to those released, should remain in the fenced plot, attracting other horses in order to prevent their immediate dispersion over the vast territory. Since the horses lose their orientation in a strange place, they should disperse gradually.
To ensure monitoring of the introduction and adaptation processes in natural biotopes.
To give assistance to the horses that failed to tolerate the severe conditions (additional feeding, etc).
The release places should meet the following requirements:
Location in the regions of zonal Mongolian steppes or the mountain steppes in the semi-arid zone.
Available reserved territory of 250–500 square km.
Available optimal grazing lands, man-made or natural water reservoirs.
Ban on hunting (game refuge) or setting up of a reservation in the given area.
Introduction of certain limitations on maintenance of domestic horses, to shoot off the feral horses, if necessary.
A number of mountain steppe areas in the semi-arid zone of
Mongolia, on the border of the breeding zones of domestic horses and camels may be suggested as possible places for the future introduction since they meet the above mentioned requirements. They are the northern part of the Gobi Reserve (Dzakhoi), the mountain region of Ushougin-Nuru and a number of similar areas.
Mountain steppes in the small isolated mountain ranges, 30–50 km long are suitable for release places. The vast steppe areas stretch between low mountain ranges, in the valleys. As a rule, they are the modern or historic range of the mountain sheep. By their natural conditions they are similar to the habitat of the wild horse. The presence of the mountain sheep may serve as an indicator of suitability of a given region for the introduction of the wild horse.
If the introduction process is considered in more detail, including the timetable for the realization of separate stages, it would be as follows:
During the organizational stage of Przewalski horse reintroduction the following steps are taken:
To choose the places for semi-reserves in the USSR and the MPR, to agree upon the conditions of their financing.
To settle administrative and juridical problems as regards the establishment of such semi-reserves.
To design and to build semi-reserve centres.
To provide logistics.
To train the research and technical staff.
To set up a base of genetic, ecological and veterinary control.
All these activities may be completed in 1986–1987. It should be kept in mind that realization of this programme is possible only under the conditions of thorough scientific and veterinary control. Therefore, it is binding to ensure the creation of ecological, genetic and veterinary control services when drafting such a programme.
The semi-reserves in the USSR and in the MPR should be financed and function during all the project period (1986–1991).
In order to fulfil the goals of the first stage of the project, upon setting up of semi-reserves in the USSR, the following steps should be taken:
To make a demographic assessment of the horses provided by the European and American zoos.
To introduce a quarantine period.
To select and to form the groups.
To ensure the initial adaptation.
To organize reproduction and production of the offspring.
To make preparations for reintroduction: to form social units, to select the best ones (from the point of better adaptability).
To carry out monitoring of the adaptation processes.
The programme of the first stage of the project may be realized in 1987–1989.
When fulfilling the goals of the second stage of the project as regards the adaptation of Equus przewalskii in the Adaptation Centre in Mongolia the following activities must be ensured:
Transportation of the adapted horses and of their offspring to the semi-reserves in the MPR.
Formation of groups; ensuring adequate ecological response of the horses to the environment.
Organization of reproduction and production of the young stock.
Preparation of horses for the next stage.
Monitoring of the adaptation processes.
The realization of this stage may be started when the horses go through adaptation for the period of 1987–1990.
At the third stage of reintroduction the following activities should be carried out:
Transportation of horses from semi-reserves.
Holding for a certain period.
Release into nature of a part of horses (harems and bachelor groups).
Monitoring of the introduction processes.
Providing assistance to the horses failing to withstand the environmental pressure.
That stage may be realized upon acclimatization of the horses in a semi-reserve centre in the MPR in 1989–1991.
During the initial adaptation in the reserves of the first stage the horses may be shipped by groups into the conditions of the second stage; and they will be replaced by other horses, provided by the zoos. Following the same order, the horses, adapted in the Adaptation Centres of the Kazakh republic and Mongolia may be transported from the places of their release into the wild. At the same time the deserted enclosures may be occupied by the horses that went through the previous stage. Thus the continuity of the adaptation process and introduction will be ensured.
Upon the release of the first groups of horses into nature it is necessary to go on with this process, to feed the developing population with new genetic resources. This would assist in stabilizing the ecological adaptation of the population in the biocoenosis and stimulating the social and reproduction processes.
In order to establish a stable and genetically balanced population of wild horses in a particular steppe biotype it is necessary to reach the efficient number of 500–700 animals. Hence the real number of a wild horse population in nature should be about 2000 head. It may be necessary to establish several populations of the wild horse. This will allow the extension of the response norm of the adaptive characteristics of this species leading to a greater diversity of its gene pool. Later, a gene pool exchange between these populations can be arranged.
When the wild horse population reaches its optimal size and reproduction is stabilized, the surplus animals can be withdrawn from the natural biotypes and shipped back to the zoos, that previously provided horses for introduction. Such a condition will undoubtedly serve in involving to a greater extent the donor zoos in the process of introducing the wild horses into the wild.
In order to ensure monitoring of the developing horse population or several populations it is necessary to set up a research station in the places of horse release.
All those participating in the project and the experts in this field from the various countries concerned will undoubtedly have the possibility to work at this station, to carry out studies.
A number of important issues, both specific and general, should be discussed within the framework of this problem. The problem of adaptation that we are facing when reintroducing the horses is one of the most important. It is necessary to find out in what way the formation of morphological and behavioural characters is proceeding, e.g. what is the process of social alliance formation, of gaining skills, of development of the territory and of reproduction. What is the role of natural selection and in what way is it manifested?
Another important problem arises as regards the functioning of a horse band in a particular steppe biotype. Preliminary studies should be carried out to assess the needs of a wild horse population for energy and feeds, the productivity of certain steppe biotypes and their response to the pressure, namely the wild horses. This makes it possible to determine the optimal density and the size of the horse groups in reserves, adaptation centres, and natural ecosystems.
It is also necessary to study the problem of conservation of the gene pool of captive horse populations. Line breeding, rotation of the genetic material (horses), and its division into separate breeding groups will be efficient.
Ways of cryoconservation of germ plasm, of artificial insemination and other forms of conservation and enlargement of the horse gene pool should be sought.
Nevertheless, we should not forget that the gene pool of the feral horse populations is no less valuable. Such horses exist in the USA, Europe, and in the Soviet Union. Being out of man's control and having adapted to the natural biotypes these horses have partially returned to the wild mode of existence of which they were deprived in the past by man. At present, taking into account the degeneration of the pure lines of horses that are bred in captivity, the use of the feral horse gene pool may have a positive effect on heterozygosity, reproduction and productive properties of the domestic horses. That is why the feral horse populations should be preserved, raised and utilized.
Having analysed the present state of Equus przewalskii as a species, preserved only in captivity, it must be admitted that such a situation is dangerous and to ensure its survival the most radical measure will be to release the horses into the wild. To achieve this, an International Project should be set up under the auspices of UNEP. It is assumed that with the use of the existing information and the capabilities of the USSR within the framework of such a Project the introduction of the Przewalski horse into nature will be a success. At the same time it is necessary to organize the concurrent activities in preserving the gene pool of the Przewalski horse in captivity as well as of that of the feral horse.
Yu. Musienko, N. Krylov, N. Lobanov and V. Klimov
Since it is impossible to preserve a species as such in captivity for a long period of time, its representatives should be returned to natural biotopes.
This idea, expressed in the decisions of numerous international workshops and meetings on the Przewalski horse preservation problems, received an enthusiastic support in the Askania-Nova reserve. In this respect, Mongolian specialists visited Askania-Nova to adopt methods of horse management and preservation, some animals were selected for introduction to Mongolia, reintroduction schemes and places for release (Gobi and Hangai piedmonts) were discussed, the programme for reception and maintenance of the horses in Bogdo-Una Reserve was prepared. At this stage the Askania-Nova reserve is eager to take part in every activity on horse reintroduction.
Since the horses accommodated in the city zoos are incapable of fighting the severe climatic conditions of Central Asia due to their poor adaptability, it is essential to set up a centre for the Przewalski horse accumulation and adaptation in the steppe zone of Europe. Such a centre could be established in Askania-Nova. The following factors may be considered as favourable:
Climate in this region is more severe than that in West Europe and the United States. Temperature in winter reaches -25–27°C. In the past this area was populated by East European tarpans.
Optimal territorial base - over 8000 ha of virgin reserve steppe to be finalized only.
Rich traditions in the management and preservation of wild horses, the Przewalski horse in particular, up-to-date experience, availability of technical experts and researchers.
The new Askania-line horses have been living for a quarter of a century and possess high adaptability to external conditions and behavioural patterns practically similar to those of wild horses, i.e. stallions form their harems, lead and protect them and successfully reproduce while mares are able to protect foals and make their own decisions.
The horses donated by European and American zoos will be able to adjust themselves to the steppe climate and acquire behavioural patterns in social environment on large areas that are essential for their normal reproduction and adequate response to changing external conditions.
To set up such a centre it is necessary to fence 8000 ha of reserve steppe, build open-air cages, connecting passages, quarantine facilities, provide water sites and reinforce the administrative and research centres.
After the zoos select horses for introduction, they will be delivered to Askania-Nova. Here they are placed in quarantine and released into enclosures according to the lines they represent. In doing so, records will be made of compatibility of the lines, increased genetic diversity and gene pool, etc.
In large enclosures groups will be formed that will serve as reproductive cells of the general population. It is suggested to mate the Askania-line stallions with the zoo mares. This is based on the fact that they possess socially adequate behaviour expressed in organization of the reproductive processes: formation of the band, its protection, management and reproduction itself. The stallions to be received can form bachelors' groups, i.e. genetic reserves of the population. In due course, it will be possible to combine several groups and bachelors on larger areas. This will enable the strongest stallions to lead harems. As a result, the population will inherit geno- and phenotypical features of the best stallions, enhancing the population's viability.
The groups function in isolated or common enclosures, get adjusted to natural conditions of the region and produce foals in a year.
Ideally wild horses should propagate under semi-reserve conditions by a population consisting of several functional harems as well as group and solitary bachelors. The horses, involved in natural reproductive processes within the population, acquire behavioural patterns inherent in free-living species representatives.
Due to the competition between stallions the strongest win a greater number of mares and superiority in reproduction. This factor will positively influence the size of their gene pool but lead to decreased effective number of the population. Therefore, natural reproduction should be controlled by man. Excessive harems are divided into several groups so that each group includes 5–7 females with the greatest possible number of harems. This will involve as many males and females in reproduction as possible and increase the effective number of the population, on the whole.
Stable reproduction in this centre will be secured only with effective number reaching 100 individuals.
After 1–2 year acclimatization some horses and offspring can be returned to the donating zoos to improve reproduction of their horses. In the Przewalski horse line breeding this centre will stimulate reproduction of horses of different lines and enrich the total population's gene pool, on the whole.
Primary adaptation will select horses best-adjusted to new environment basing on physiological condition, density of winter hair coat, timely shedding, adequate social behaviour in intragroup, intergroup and interspecies relations, involvement in hierarchical and reproductive competition, actions taken in extreme situations. These animals will be prepared for the second stage - introduction into the wild. They will form separate groups or the best will be selected from existing reproductive groups. The evidence accumulated through behavioural studies of the Przewalski horses in Askania-Nova shows that the reproductive cells, formed without man's intervention and including all the age groups are most adaptable to the environment. In this case the group acts as a functional system implementing vital functions of feeding, protection, self-government and coordination response to external stimuli. These functions are not fully expressed or lost in the groups incomplete in number or composed of young stock. As a result, such groups are not able to withstand environmental pressure and preserve their gene pool. Therefore, in our opinion, the introduction should involve the groups that have been formed on their personal attractions and affections. These groups will be able to protect themselves in any serious situation, preserve and hand down the genetic material to succeeding generations. This proves it necessary to transport the entire reproductive groups to their introduction sites. It will facilitate their travel and adaptation upon arrival.
The centre will be carrying out ecological and genetic monitoring and various biological studies in the course of the zoo horses' adaptation.
The horse management techniques will be mastered in relation to immobilization, cryoconservation of sperm and artificial insemination, monitoring of social dynamics (adaptation) and daily activities. Such work will require immobilization drugs (ethorphine and antidote), appropriate equipment and chemicals.
The centre can train Mongolian and other countries' specialists in the wild horse management methods.
The Przewalski horse adaptation in Askania-Nova and reintroduction to Mongolia will entail:
Stage I - 1986–1987: Establishment of Przewalski Horse Adaptation Centre in Askania-Nova
Allocation of funds, definition of legal and financial status.
Fencing of 8000 ha of reserve steppe with mesh.
Building of quarantine facilities, open-air cages, sheds, administrative offices, laboratories, cottages for experts, drilling of artesian wells, arrangement of watering and salting sites.
Preparation of materials for veterinary control and research: immobilization drugs, medicine and equipment.
Establishment of zooveterinary and monitoring services.
Stage II - 1987–89: Definition of Number and Sex Ratio of Horses to be Donated by Zoos
Delivery of horses from the zoos.
Identification, marking, quarantine.
Formation of breeding groups and their adaptation.
Organization of reproductive processes, production of offspring.
Formation and preparation of groups for their transit to Mongolia.
Research, genetic and ecological monitoring.
Stage III - 1988–89:
Transit of the horse groups to Mongolia, introduction.
Measures aimed at the improved line breeding: international exchanges, rearrangement and rotation of genetic material.
As one can see, successful introduction of the Przewalski horses into the wild is feasible. Upon adaptation in Askania-Nova, there are no causes for concern over their life in natural biotopes since their survival will depend on properties they have acquired under semi-reserve conditions of the centre.
The Przewalski horse reintroduction will succeed only thanks to the comprehensive and coodinated efforts of all the people and institutions interested in preservation of the last wild horse on the earth!
Thomas J. Foose
Small populations, whether in captivity or the wild, are subject to a number of genetic and demographic phenomena and problems that affect their survival over both the short and the long term.
The major genetic problem is loss of heritable variation or diversity. Genetic diversity seems critical at the population level to permit adaptation to changing or changed environments and at the individual level to sustain vigour in terms of survivorship and fertility (Frankel and Soule 1981). The primary causes for erosion of genetic diversity in small populations are random genetic drift and founder effect (Crow and Kimura 1970).
Genetic drift is caused by the random segregation of genes into gametes and hence from parents to progeny. Founder effect is caused when a new population is established with a few individuals from some other source. Both genetic drift and founder effect represent sampling processes in which only some fraction of the entire gene pool of the parent generation or source population is propagated.
Loss of genetic diversity due to random drift is a function of the size but also the structure and dynamics of a population (Crow and Kimura 1970). Very generally, the smaller the population is, the faster genetic diversity is lost (Figure 1). This phenomenon is true in captive or wild populations.
However, the population size of relevance is not merely a total census of all the animals alive. Instead, the genetically effective size (Ne) of a population is a measure of the way in which animals are actually contributing to the next generation of progeny. Disparities in the sex ratio and inequalities in the lifetime production of offspring (i.e. family size) will reduce the effective size Ne of any total population N (Figures 2 and 3). An animal that does not reproduce during its lifetime does not contribute to Ne at all. A male that dominates breeding for a long time may contribute excessively and therefore also reduce Ne. The Ne of a population of ten horses composed of 1 male and 9 females is 3.6, even though the total population N is 10.
Thus, Ne is a function of the social structure and dynamics of a population. Depending on what these characteristics are, the Ne can vary from a tenth to twice the actual number of animals. In natural populations, the social organization is usually such that the genetically effective size is less than the total number. Ne/N ratios of .5 or less seem likely to be common. Management can alter the genetically effective size of a population.
Fig. 1 Decline of genetic diversity for various effective population sizes (Ne) possible for a total population (N) of 250
Fig.2 Effect of sex ratio on effective population number
Fig. 3 Effect of variance in family size on effective population number
Fig.4 Effective population size and generation times for maintaining 90% of Genetic Diversity for 200 years
Conservation of the gene pools of species requires that minimum viable populations (MVPs) be maintained. MVPs depend on a number of factors (Figure 4) (Soule et al. 1986; Lande and Barrowclough 1986):
The Ne/N ratio that can be expected from the natural behaviour of the population or that can be produced by some management.
The amount of the gene pool it is acceptable to preserve, for example 90%, 95%, 100%.
The time scale over which the conservation management is to occur, for example 200 years or indefinitely.
The generation time of the species.
Loss of diversity occurs generation by generation. So any absolute period of time, for example 200 years, is a different number of generations for various species. For example 200 years is about 17 generations for Przewalski horses whose generation time is about 12 years, but 25 generations for Amur tigers whose generation time is about 8 years. Thus, if their Nes are equal, Amur tigers would lose more genetic diversity over 200 years than Przewalski horses would.
5. The size of the initial or “founder” population (Figure 5).
It is impossible to preserve more genetic diversity (over time periods on the order of several centuries) than a newly founded population originally possesses. The animals that found a population may or may not contain all or most of the genetic diversity in the source population. A founder is defined as an animal from a source population that actually reproduces in the new population. The recommended numbers for MVPs assume that founders are unrelated and non-inbred. If these conditions do not pertain, larger numbers of founders may be recommended. More founders are usually better, but there is a point of diminishing returns. A sample of 20–30 founders will normally contain well over 90% of the average genetic diversity in the source population (Soule et al. 1986).
Thus, the number and background (genetic characteristics) of founders should also be considered, and in relation to number of potential reserves. It will probably be desirable for multiple or repeated infusion of founders to occur (Figure 6).
6. The reproductive potential or growth rate of the population.
More important than number of founders will be rate of growth of population from its initial to a carrying-capacity or MVP size. If the founder number is much lower than the carrying capacity, considerable genetic diversity can be lost during the growth phase unless expansion of the population is very rapid.
Relationship between effective population size, generation length and founder group size required to
maintain 90% of original genetic diversity for 200 years.
A-No founder effect B-20 founders C-8 founders D-6 founders
Assuming immediate expansion of founder groups with no loss of diversity (modified after graphics prepared by M. Soulé and J. Ballou.)
(From Conway 1986)
Fig. 5 Population size, founder size, generation time and preservation of diversity
Fig. 7 Forces affecting amount of genetic variation in small populations
7. The nature and intensity of selection, artificial or natural.
Selection can operate either to maintain or diminish genetic variation in small populations. Past effects of selection (conscious or unconscious) in the captive population of Przewalski horse are not well known (Ryder and Wedemeyer 1982; Dolan 1982). But, choice of founders for reintroduction, at least initially, should encompass the widest possible range of the genotypic and phenotypic variation still present in the captive population to provide natural selection in the reserves with the greatest possible base on which to operate. Thereafter, selection in the reserves could either be restricted to what naturally occurs or could be applied artificially for more intensive genetic and demographic management.
Based on these considerations, minimum viable population (MVP) sizes can be recommended to sustain desired levels of genetic diversity for prescribed periods of time within the constraints of the biological characteristics of a particular species. Reserves should be constituted to achieve carrying capacities equal to or preferably greater than MVPs.
Genetic drift can be counteracted by mutation, selection (natural or artificial) or migration (gene flow from a different population) and therefore may modify recommendations from MVPs (Figure 7). Subdivision of a population, which in the context of reintroduction of the horse is equivalent to establishment of multiple reserves, may enhance maintenance of diversity.
Reserves should be established so that their size, shape, and number will accommodate minimum viable populations. In the case of the Przewalski horse, it seems advisable that there initially be at least two reserves each with a potential carrying capacity of several hundreds of animals.
Matters of growth rate and carrying capacity indicate importance of demographic problems and management for small populations. Small populations are also very vulnerable to problems of demographic fluctuations and stochasticity which can cause extinction (Goodman 1986). Obvious examples of stochastic perturbations are disease epidemics, and natural disasters. More subtle problems include distortions of sex ratio in the few births that might occur in a small population or low densities that inhibit potential mates from locating each other.
Deterministic (nonstochastic) demographic problems can be of equal or greater importance. Demographically, a population can be analysed and managed by three basic parameters: the age specific survival rates; the age specific fertility rates; the number and ages of the population at any time (Goodman 1980). In captivity, Przewalski horse populations manifest growth rates of 10% or more per year (Figure 8). Feral populations of domestic horse in North America manifest annual growth rates of 10–20% per year. Such growth rates are very vigorous and can eventuate in population explosions that must be regulated.
Rate of growth depends on the patterns of survival and fertility (Figure 9). Ultimately, small populations need to be stablized at the determined carrying capacity (Figure 10). Stabilization of populations can occur by: (i) regulation of reproduction, in other words some kind of birth control, (ii) removal of animals (Foose 1983).
(From Conley 1980)
Fig. 10 Conversion of horse populations to stationary condition
|Annual rate of increase before harvest||Population size||Harvest||Annual rate of increase after harvest|
However, demographic management must also be cognizant of the age structure of populations. Regulation of numbers is impossible without stabilization of age structures. Populations will normally require some combination of regulation of reproduction and removal of animals for stabilization.
The demographic characteristics of founders will affect rates of population expansion and hence should be considered in selection of animals for reintroduction. A measure of the relevant demographic characteristics is known as the reproductive value (Goodman 1980).
Considering both genetic and demographic concerns, a system of interactively managed captive and wild populations seems optimal (Figure 11). It will be vital to ensure the security and integrity of the captive populations both genetically and demographically while providing viable stock for reintroductions. Sustainable “harvests” of a limited number of horses each year for reintroduction should be possible without preventing the captive population from continuing its growth to and stabilization at the desired carrying capacity or without depriving the gene pool in captivity of essential variation (Table 1).
Indeed, limited and periodic exchange of genetic material in both directions between captive and wild populations will be beneficial to both.
However, it is imperative that genetic and demographic developments in the reintroduced herds be closely investigated by well organized follow-up studies subsequent to release (Price 1986).
Conley W. 1980 The potential for increase in horse and ass populations: a theoretical analysis. Scientific Paper 131, Agricultural Experiment Station, New Mexico State U., Las Cruces, NM 88003.
Conway W.G. 1986 The practical difficulties and financial implications of endangered species breeding programs. In: International Zoo Yearbook 24 (in press).
Crow J.F. and Kimura M. 1970 An Introduction to Population Genetics Theory. Harper and Row, New York.
Dolan J.M. 1982 Przewalski's horse in the United States prior to 1940 and its influence on present breeding. Der Zoologischer Garten 52:49–65.
Foose T. 1983 The relevance of captive populations to strategies for conservation of biotic diversity. In: Genetics and Conservation. C. Schonewald-Cox, S. Chambers B. MacBryde and L. Thomas (eds). Benjamin/Cummings, Menlo Park, CA.
Frankel O.H. and Soule M.E. 1981 Conservation and Evolution. Cambridge University Press, Cambridge.
Goodman D. 1980 Demographic intervention for closely managed populations. In: Conservation Biology. M.E. Soule and B.A. Wilcox (eds). Sunderland MA, Sinauer Associates. pp. 171–195.
Goodman D. 1986 The minimum viable population problem. I. The demography of chance extinction. In: Viable Populations. M.E. Soule (ed). (in press).
Lande R. and Barrowclough G.F. 1986 Effective population size, genetic variation and their use in population management. In: Viable Populations. M.E. Soule (ed). (in press).
Price M.S. 1986 Reintroduction of Arabian oryx into Oman. International Zoo Yearbook 24 (in press).
Ryder O.A. 1982 and Wedemeyer E.A. A cooperative breeding programme for the Mongolian wild horse Equus przewalski in the United States. Biological Conservation 22: 259–272.
Soule M.E., Gilpin M., Conway W. and Foose T. 1986 The millennium ark: how long the voyage, how many staterooms, how many passengers? Zoobiology (in press).