Record keeping

Animal record keeping is the foundation of captive animal management. Zoo professionals depend on detailed direction from animal records. Mammals with missing or unknown ancestry or other life history information are of very limited use in long term management strategies. The International Species Information System (ISIS), first developed in 1973, collects animal data from over 560 institutions in 72 countries on 6 continents and stores them in a computerized database. These data are kept by a computerized program called ARKS (Animal Record Keeping System). Much of the data are entered into a computer software program called SPARKS (Small Population Analysis and Record Keeping System) by a studbook keeper, in order to produce a studbook. A stud-book is an inventory of the life history and ancestry of an animal and SPARKS can perform mathematical analyses of studbook data. From SPARKS one can get age class and sex class graphs as well as survivorship and mortality data for a population. It can also generate many useful reproductive

Modern zoos try to recreate the animals' natural environment, as with this cheetah (Acinonyx jubatus) cub. (Photo by © Lynda Richardon/ Corbis. Reproduced by permission.)
This lar gibbon (Hylobates lar) takes advantage of the climbing system installed in its zoo habitat to allow more natural behavior. (Photo by © Robert Holmes/Corbis. Reproduced by permission.)

analyses. In order to formulate a population management plan, SPARKS data are exported to a software program called PM2000. This is a powerful computer program that can generate, among other things, target population size, generation time, growth rate, and current percent of genetic diversity. It also allows the user to build preferred breeding pair calculations, so recommendations can be made by the population manager.

Techniques for small population management

Incorporating profound knowledge and documentation of genetics and principles of population biology, Ballou and Foose (1996) describe specific guidelines for efficient demographic and genetic management of small populations. These guidelines are used extensively by zoological gardens in an attempt to achieve long-term survival of small populations. Their basic techniques are summarized here.

FOUNDER REPRESENTATION

The long-term survival of a small population depends upon obtaining a sufficient number of founders to maximize allelic diversity and heterozygosity. The goal here is to obtain enough unrepresented animals to build a population that will represent a cross-section of the genotype and phenotype of the source population. Unfortunately, one cannot predict the quality of the sample because it cannot immediately be measured. Founder numbers are considered adequate for effectively sampling allelic diversity based on the most likely allele distributions. Genetic variation over the range of the source population should also be considered, with between 25 and 50 founders considered sufficient in most cases.

REACH CARRYING CAPACITY

Carrying capacity in zoos is the entire number of spaces available for a particular species among all program participants. In order to maximize genetic efficiency the population size should be increased as rapidly as possible in order to meet the carrying capacity. Genetic diversity is lost when growth rates are slow, because the chances of all animals in that population successfully reproducing and being represented in the first generation decreases with time.

STABILIZE THE POPULATION

The population should be stabilized once it is near the carrying capacity. The current population size and growth rate are used to determine the proximity to carrying capacity and the population is stabilized by regulating birth control. Birth control of mammals in zoos is achieved both biologically and by the physical separation of animals.

EXTEND GENERATION LENGTH

Mean generation length is defined as the average age at which the females in a population produce offspring. Since genetic diversity is lost with each successive generation, extending the generation length reduces the degree of diversity lost in a small population over a given number of years. In other words, if the females in a population do not breed until later in life the loss of genetic diversity is delayed. Risk is incurred with this strategy since the animal's reproductive potential may be lost with time, due to age related fertility problems, health problems, and accidental injury or death.

ADJUST FOUNDER LINEAGES

In order to maximize the genetic diversity and survivability of a captive mammal population the representation of founder lineages should be as proportional as possible to the distribution of founder alleles surviving in that living population. Initially in a captive population some animals will reproduce well and be highly represented genetically while others will not. Therefore, the population will not be evenly represented genetically. In order to compensate for this, preferential breeding pairs should be formed. Descendants of un-derrepresented founders should be preferentially bred and the reproduction of overrepresented animals should be limited.

REDUCE THE REPRESENTATION OF EXTREME TRAITS

Reproduction should be limited in animals that produce traits that are not typical or that would offer a selective disadvantage to survival in the natural environment. Albinism is an example of such a trait.

SUBDIVIDE THE POPULATION AND REGULATE GENE FLOW

Division of a large captive population into geographically isolated subunits offers some advantages. The exchange of animals as well as gametes between these subunits should be regulated. This method offers increased protection to the population from communicable diseases and natural disasters such as fire, earthquake, tornado, and hurricanes. Also, isolated subunits of the population will be exposed to a wider range of selective pressures. This offers the advantage of a slowed reduction of genetic diversity.

INTRODUCE NEW FOUNDERS

The addition of new founders should, in theory, increase genetic diversity. If a program can be devised to exchange wild caught animals for captive born ones, this can sustain a population. However, great care must be taken to eliminate the possibility of disease transfer between the populations.

INCORPORATE REPRODUCTIVE TECHNOLOGY

Emerging advances in reproductive technology can be used to increase genetic diversity and sustain a captive population. Genetic material such as semen, ova, embryos, and tissues can be stored and used at a latter date. This can increase the chances of a genetically underrepresented animal being utilized in a population. It can also increase the practical aspect of introducing new founders from wild populations. It is much easier and safer to move an animal's gametes rather than to physically transfer the entire animal.

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