The End of the Road or the Beginning of a Journey?
An Exploration into the Survival of the Tiger
By Annie White
December 12, 2001
Since the time of Pharaoh Amenhotep III, humans have hunted the tiger (Meachman 1997). Over the last three thousand years, the relationship between human and tiger has changed little. The tiger (Panthera tigris) requires dense forests, abundant prey, and large tracks of undisturbed land. From the beginning, humans have cut down the lush trees, hunted the large game animals, and driven the tiger into small corners of the world. Despite the onslaught, tigers had persevered up until the 1900s. First the Bali, then the Caspian, and then the Javan tigers fell into extinction. Now, the Bengal, Indochinese, Amur, and Sumatran cats are headed in the same direction. The South China tiger is teetering on the brink of extinction.
Seemingly insurmountable obstacles stand in the way of the tiger’s recovery from endangerment. Illegal poaching and trafficking is rampant in all of the 14 countries where tigers are indigenous (Ives 1996). All parts of a tiger’s body are in high demand on the Chinese black market as cures for medical ailments (Meacham 1997; Plowden and Bowles 1997; Tilson 1998). Deforestation and habitat loss have also contributed to the rapid decline in the tiger population (Seildensticker et al. 1999). Only small islands of forest remain among the expanding agricultural areas of many Asian countries. This isolates tiger populations from each other and promotes inbreeding in the few tigers left in a given area. Inbreeding weakens the gene pool and can eventually lead to a rise in birth defects and mutations (Hemmer 1978; Newman et al. 1985). Many countries are now realizing the position in which their tigers have been placed, and are starting to conduct studies and create management plans for the sparse tiger populations. In order to begin on such a daunting task, an inventory of each subspecies must first be taken.
By far the most populous of the five surviving subspecies, the Bengal tiger, or P.t. tigris, numbers from 3,159 to 4,715 in the wilds of India, Nepal, Bangladesh, Bhutan and Myanmar (Tilson 1998). Despite the recently increasing levels of poaching, these cats are considered secure in the wild for the moment. The 1997 International Tiger Studbook only listed 210 of the 333 captive Bengal tigers because many of the cats are of questionable lineage, making them useless in the preservation of the subspecies (Tislon 1998).
The last 1,500 wild Indochinese tigers, P.t. corbetti, are spread out over Thailand, Myanmar, Southern China, Cambodia, Laos, and Malaysia. Severe human encroachment, habitat fragmentation, population isolation, heavy poaching and trafficking, and the lack of established zoos and Wildlife Departments have lead to a significant threat to these wild tigers. There are 60 Indochinese tigers held in captivity at present; however there is an extremely low number of founders contributing to the population’s gene pool (Tilson 1998).
P.t. altaica, also known as the Amur, Siberian, Manchurian, or Northeast China tiger is the largest of all the tiger subspecies. Due to its long fur, deep colors, and sharp contrast to the white of winter snow, the Amur has become very popular with the worldwide public, thus gaining greater support for conservation projects. Between 360 and 406 wild Amur tigers roam in North Eastern Russia (Tilson 1998). The purity of the wild Amurs in Russia is unknown, but the survival of the subspecies depends on them, for there are fewer than 35 remaining in China (Flesness and Cronguist-Jones 1987). With a captive population of 501, this is, by far, the largest and most stable program to date. Since 83 wild-caught animals founded these captive tigers, the Amur is considered a secure and genetically diverse population (Prinsee 1992).
A tiny Indonesian island is home to the last 400-500 wild Sumatran tigers, P.t. sumatrae. Over the last two decades, Sumatra has undergone great agricultural development. Deforestation and fragmentation have made the remaining tiger populations very vulnerable to poaching as well as government control of problem animals. Recent research on the 210 captive Sumatran tigers has revealed the possibility that it is not a subspecies of Panthera tigris, but a completely separate species of tiger (Ballou and Seidensticker 1983; D.S. 1998; Goebel and Whitmore 1987; Hemmer 1987; Seidensticker et al. 1999).
The most gravely endangered of the subspecies, P.t. amoyensis, or the South China tiger, has virtually disappeared from the wild. There have been no sightings of this tiger in the wild by Chinese officials for over twenty years, while optimistic reports suggest that as many as 20 to 30 still exist in the wild (Tilson 1998). The South China Tiger is considered by scientists to be the evolutionary antecedent of all of the tigers (Herrington 1987). Little hope remains, as there are only 67 cats in captivity, all descended from six wild founders (Tilson et al. 1997).
It soon becomes apparent that all of the tiger subspecies face unique, yet serious problems. Debate about the most effective and feasible conservation plan for the tiger rages on as fewer are found in the wild each year. Some want to interbreed the five remaining tiger subspecies to create one generic, but genetically diverse and populous, tiger. Others want to preserve the integrity of the separate subspecies through carefully managed breeding programs. It could be that some combination of the two plans is needed, along with continued public education and wilderness protection in order to preserve the tiger.
Preserving Natural Selection
A majority of scientists believe that an effort must be made to preserve all five of the remaining tiger subspecies. There are organizations spanning political and international borders, working on management programs and protection for the cats. An emphasis has been put on developing captive populations and breeding programs in the hopes that when the last tiger disappears from the wild, there will be enough living in zoos to survive into the coming centuries. The Global Conservation Strategy (GCS) has been formed to oversee and coordinate the many management programs in Europe, Indonesia, China, Thailand, Japan, Australia, India, and North America (Wildt et al. 1993). The GCS manages the captive tiger populations to maximize the genetic diversity and stability of each of the five subspecies (Wildt et al. 1993).
It is a delicate and difficult balancing act, but people are slowly learning how to manage genetically diverse captive populations while staying within the strictures of funding, space, politics, and scientific information. The Species Survival Plan (SSP) has taken over the role of balancing these important factors (AZA 1998). For each subspecies, a masterplan is being developed for the breeding of individual captive tigers for maximizing their genetic diversity (AZA 1998). The members of the contributing population of tigers are entered into a subspecies-specific international studbook. This allows each individual tiger to be monitored for kinship, age, fecundity, inbreeding, founder origins, and location (Tilson 1994). In weighing all of these elements to decide which animals should be bred, the SSP must also take into consideration the limited amount of space available in zoos, limited monetary resources, and political issues dredged up in the international arena (AZA 1995; AZA 1996). The goal of the SSP is to maintain a population of each subspecies of tiger with a gene diversity of 90% for 100 to 200 years (Tilson 1998).
Along the same lines, the Tiger Missing Link Foundation and the American Tiger Registry are attempting to manage the genetic diversity of tigers within the private sector (Werner 1999). Through registering and testing the DNA of privately owned tigers in America, it is hoped that this population can contribute to the conservation-breeding program. This endeavor has already contributed much to the scientific knowledge of the great cats. Microbiological studies have mapped the specific sites at which genetic differences show up among felids (Cracraft et al 1998). With further study, it may be possible to take the gene map of any given tiger and determine its subspecies or hybridization (Werner 1999). This would allow for closer control of gene flow through a population and would help in defining the perimeters of each subspecies or species, as the case may be. These same studies have concluded that there are significant genetic differences between subspecies to warrant preserving them individually. It is hoped that through the efforts of the GCS, SSP and the private sector, all five of the subspecies will survive.
The Generic Brand Tiger
Others believe the traditional scientific approach to species conservation is inappropriate in the tiger’s case. They see the genetic similarity among the subspecies as an indicator that there is not a founded reasoning behind the designation. All tigers have a common ancestry; that of the now greatly endangered South China tiger (Hemmer 1987). Thus, some people believe the world’s entire population of tigers should be bred together so as to benefit from the widened genetic pool (Kitchner and Dugmore 2000; Singh 1995; Tickell 1998). They ask the question, “Does it matter whether they are Bengal or Sumatran as long as there are tigers in the world?”
In justification of such an unorthodox method of preservation, the nature of the subspecies classification needs to be taken into consideration. It was not long ago that there were no recognized tiger subspecies classifications (Hart-Davis 1997). The distinctions are drawn by geographic boundaries. This would seem logical because geologic boundaries tend to isolate certain populations from each other. In the case of the tiger, this does not necessarily hold true. Water bodies are commonly used as boundaries between tiger subspecies, however a single river is not likely to separate two tiger subspecies for long. Some have hypothesized that the subspecies distinctions are based on attributes, such as size, color and behavior, which are influenced by environmental rather than genetic factors (Kitchner and Dugmore 2000). Though these hypotheses are in direct contradiction to the results found by Cracraft et al. (1998) and Werner (1999), the actual genetic relationship of tiger subspecies is vague and much disputed. If Kitchner and Dugmore (2000) were correct, the environmentally induced traits would reappear in a generic tiger once it was reintroduced to a particular habitat.
Reducing the biodiversity of the earth is rarely included in a wildlife management plan. However, in this case, it may be necessary. Each subspecies of tiger has a very limited gene pool. Inadequate gene diversity can lead to inbreeding and eventually to weakened and unhealthy tigers. If the genes from all of the subspecies were available for breeding, then healthier animals would be produced. Under this theory, it is not the genetic distance between subspecies, but that of individual tigers, that would provide the diversity at each gene locus needed to prevent inbreeding depression. Thus, it may be that in order to preserve the tiger for future generations, the genetic diversity of the separate subspecies must be sacrificed (Hart-Davis 1997).
The Fate of a Species
There are merits and drawbacks to both of the general plans posed by conservationists. In preserving all of the subspecies, we stand a chance of strangling the remaining populations with inbreeding. However, if there is a significant difference in the subspecies, it is our duty to try to preserve it. A healthier population could come of creating a generic tiger, yet we run the risk of permanently destroying the unique characteristics of the subspecies. In the past, humans have made grave mistakes in conservation efforts. The dusky seaside sparrow is just one example of scientists attempting to save a species, without the proper scientific research beforehand. Despite all of their efforts, a unique species was hybridized with very different sparrows; consequently the dusky seaside sparrow was forever lost (Meffe et al. 1997). There must be more research into the molecular and genetic characteristics of the tiger subspecies to determine if they are indeed subspecies, separate cryptic species, or one species spread out over a large range. However, time is running out for the tiger, and we cannot wait for the results of tests and studies to take action. While the studies are conducted, all efforts must be made to preserve the genetic diversity of the tiger as well as sustainable numbers.
The best scenario, at this point, would be to carry out both plans simultaneously. It has been shown that tigers do not have a problem reproducing in captivity (Wildt et al. 1993), so theoretically, it should be possible to produce a generic tiger race as well as selectively breed individuals for subspecies preservation. Regardless of the theoretical benefit, however, logistics will not allow this to happen. Limits in funding, time, transportation for the breeding pairs, knowledge of alternative breeding techniques, and space, put vast constraints on the reality of what can be done (Karanth and Madhusudan 1997). Three specific steps can be taken to lessen, if not eliminate, the pressures these factors impose on the tiger conservation effort.
First of all, the public must become more informed and involved in the process. The media needs to focus on educating the worldwide public of the exact situation facing each tiger subspecies. In reaching across country borders, the publicity would elicit international concern. Since the conservation effort is an international affair, the more people in different countries that understand the crisis, the better. Through education comes interest. Through interest comes pressure on politicians to pass more stringent laws and provide more funding to the cause. Through better funding, more research and greater preservation can be done.
Second, the biological materials of as many captive and wild tigers must be collected and complied in a Genome Resource Bank. In cryogenically preserving gametes, embryos, tissues, and blood for each tiger, current genetic integrity can be protected (Wildt et al. 1993). Not only will this allow for in-depth studies of tiger phylogeny and disease, it would be used interactively with living and wild animals to intermittently infuse the population with non-represented genes. This would also allow the number of living captive animals needed to ensure sufficient genetic variations to be reduced. With the help of artificial insemination, and in vitro fertilization, a Genome Resource Bank would also reduce the necessity of transporting live tigers over long distances to ensure mating between non-related individuals. The extended generation interval of current founder tigers would greatly reduce the risks of further inbreeding (Werner 1999).
Third, a decision must be made between the two plans. Until the complete phylogeny of Panthera tigris is understood, the safest bet would be to try to preserve as many of the five subspecies as possible, while trying to overcome the restraints of limited funding, space and generation time. It is unlikely that any kind of consensus is forthcoming as to the genetic relationships between subspecies since microbiological tests are yielding such different results. In the mean time, it is imperative that the outlook for each subspecies be examined and used to determine the exact course of action.
Since the Amur, Bengal, and Indochinese tigers are relatively stable and secure for the moment, all efforts to preserve their genetic distinctions should be made. Breeding programs ought to work on specifically isolating and utilizing the strong genetic variation left in these three subspecies. If the Sumatran tiger is truly a separate species, as recent research has indicated (D.S. 1998; Goebel and Whitmore 1987; Hemmer 1987; Seidensticker et al. 1999), then a greater effort should be made to keep their bloodlines pure and work to expand the sheer number of Sumatrans living in captivity.
The extremely low population size and high evolutionary significance of South China tigers warrants a consideration of outbreeding. Evidence has shown that populations as small as the South China tigers are doomed to extinction by their lack of genetic variability. Due to their limited numbers and confined territory, it has been estimated that only one or two unrelated pairs of South China tigers remain (Tilson et al. 1997). Other research has confirmed that a minimum of thirteen unrelated pairs is needed to maintain a genetically and numerically stable population (Savage 1998). Perhaps by crossing the South China tiger with the Indochinese tiger, since they have overlapping ranges, a new and viable subspecies of tiger could be created. Hopefully, this cross would save the integrity of the South China tiger genes and passing them on to a new generation of thriving tigers. It may be possible that in introducing a generic tiger into vacant habitat in China, it could eventually evolve to fill similar niches as the original subspecies occupied. By introducing generic tigers into vacant ranges, we could essentially be giving evolution a second chance at creating new subspecies.
The Beginning or the End?
Less than a century ago, there were over 100,000 thousand tigers roaming the dense forests of Asia. Today, fewer than 5,000 remain in the wild. People across the globe are coming to realize the danger in which the tiger has been placed. Conservation plans abound, but miles of red tape and years of political and scientific argument stand in the way. There are dedicated people working for the tiger, but they cannot accomplish their goals until widespread public support, cryogenic preservation and carefully controlled breeding programs can buy time for the tigers. Without help, the tiger will vanish, never again to inspire awe and wonder in future generations or contribute to the much-needed biodiversity of the earth.
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