Chapter 16 Genetics and Management of Wild Populations Although genetic issues are of critical importance, there has been limited application of genetics in the practical management of threatened taxa in natural populations.

Key Genetic Contributions to Conservation Biology: Resolution of taxonomic uncertainties such that managers are confident of the status of, and relationships among, the taxa they strive to maintain. Delineation of any distinct management units within species, as biologically meaningful entities for conservation.

Recognition that the effective sizes of populations, that determine the genetic future of populations, are frequently about an order of magnitude lower than the census size. Detection of declines in genetic diversity. Development of theory to describe past, and predict future, changes in genetic variation. All such categories have a common, central theme -- genetic diversity is dependent upon effective population size (N e ).

Recognition that the genetic diversity underlying the quantitative variation in reproductive fitness is the raw material for adaptive evolution through natural selection. Loss of this class of genetic variation reduces the capacity of populations to evolve in response to environmental change. Direct evidence for inbreeding depression in endangered species in natural habitats.

At a practical level, potential inbreeding depression may be inferred from its correlation with reduction in genetic variation, assessed by markers. Degree of fragmentation and rates of gene flow can be inferred from the distribution of genetic markers within and among population and calculation of various population genetic statistics.

Approximate Order of Genetic Management Actions for Wild Populations:  Resolve any taxonomic uncertainties and delineate management units.  Increase population size  Diagnose genetic problems  Recover small, inbred populations with low genetic diversity in naturally outbreeding populations.

 Genetically manage fragmented populations. Resolving Taxonomy and Management Units Resolving Taxonomy and Management Units: The first step in the genetic management of wild population of threatened species is to ensure that the species’ taxonomy is correctly assigned and that any distinct management units are defined -- Go back and review the Dusky Seaside Sparrow.

Increasing Population Size Increasing Population Size: Once any taxonomic uncertainties are resolved, the next step is to halt decline and increase the size of populations. This alleviates all the stochastic threats to species. If populations have only recently declined from larger size, say 50 to several hundred, then the genetic impacts are usually minimal. Despite the bottleneck, short-term reductions of this magnitude allow little opportunity for variation to be lost through genetic drift.

This step, increasing population size, is in the domain of wildlife biologists and ecologists -- identification of the cause of the decline. While genetic information may help to alert conservation biologists to the extent of endangerment, the management action at this step involves little, or no, genetic data. However, recovery in numbers of highly inbred populations can be substantially enhanced following introduction of additional genetic variation.

Insecure wild populations can be augmented using captive bred individuals. The nene has been subjected to a long program of augmentation from captivity as its wild population does not appear to be self-sustaining. Such programs may be counterproductive in the long-term if the captive population adapts to reproduction in captivity and its reproductive ability in the wild is reduced.

Such is clearly a problem in fish where long-term captive populations, used to stock wild habitats, have lower reproductive fitness in the wild than residents. Diagnosing Genetic Problems Diagnosing Genetic Problems -- A necessary precursor to genetic management of wild populations of threatened species is to diagnose their status. We need to answer three questions. 1.Has a threatened species/population lost genetic diversity? 2.Is it suffering from inbreeding depression? 3.Is it genetically fragmented?

Answering these three questions have been the main genetic contributions to the conservation of wild populations thus far. However, using this information to plan conservation management is still in its infancy. We will now consider the genetic management actions that should be taken to alleviate genetic problems.

Recovering Small Inbred Populations with Low Genetic Diversity Diversity: An effective management strategy in the recovery of small inbred populations with low genetic diversity is to introduce individuals from other populations to improve their reproductive fitness and restore genetic diversity. There is extensive experimental evidence that this approach can be successful. For example, it improved fitness in natural populations of greater prairie chickens, Sweddish adders and a desert topminnow fish.

In spite of the clear benefits of outcrossing to recover small, inbred populations, there are very few cases where it is being done. Source of Unrelated Individuals for Genetic Augmentation Source of Unrelated Individuals for Genetic Augmentation: The individuals chosen for introduction into inbred populations, for recovery of fitness and genetic diversity, may be either outbred (if available), or inbred but genetically differentiated from the population to which they are being introduced.

When no unrelated individuals of the same taxon are available, individuals from another sub-species can be used to alleviate inbreeding depression. This has been done for the Florida panther and the Norfolk Island boobook owl. If an endangered species exists as only a single population, then the only possible source of additional genetic material is from an unrelated, interfertile species.

For example, American Chestnuts have been crossed to Chinese Chestnuts to introduce genetic variation for resistance to blight that severely depleted the American Chestnut. China is the source of the blight disease and the Chinese chestnut possesses resistance. The option of crossing a threatened species to a related species requires very careful consideration. The potential benefits need to be very large, as there may be serious risk of outbreeding depression.

Management of Species with a Single Population Lacking Genetic Diversity Genetic Diversity: From a genetic perspective, the worst situation is where an endangered species exists as a single, inbred population with no sub-species or related species with which to hybridize. Information on the level to which genetic diversity has been reduced is useful only as an indication of the fragility of the species.

The lower the genetic diversity, the lower becomes the evolutionary potential, and the higher becomes the probability that the species has compromised ability to cope with changes in its physical or biotic environment. For fragile species, management regimes should be instituted to:  Increase population size.  Establish populations in several locations to minimize the risk of catastrophes.

For example, in the case of the black-footed ferret, where there is low genetic diversity, the recovery plan calls for re-establishment of 10 wild populations, in different locations, to minimize the risks of disease and other environmental catastrophes. Maximize their reproductive rate by improving their environment (e.g., removing predators and competitors).

Insulate them from environmental change. This should include quarantining from introduced diseases, pests, predators and competitors, and monitoring, so that remedial action can be initiated as soon as new environmental threats arise. Genetic Management of Fragmented Populations: Many threatened species have fragmented habitats and the management options for these fragmented populations is to maximize genetic diversity and minimize inbreeding and extinction risks through:

 Increasing the habitat area.  Increasing the suitability of available habitat  Artificially increase the migration rate via translocation however, translocation of individuals among populations may be costly, especially for large animals, and carries the risks of injury, disease transmission and behavioral disruption when individuals are released.

For example, introduced males lions regularly kill cubs. Furthermore, sexually mature males of many species may kill intruders. The cost of translocations can be reduced by artificial insemination for species where this technique has been perfected.  Re-establish populations in suitable habitat where they have gone extinct.

 Create habitat corridors. Corridors among habitat fragments can re-establish gene flow among isolated populations. Species vary in their requirements for a corridor to be an effective migration path. The most ambitious proposal of this kind is The Wildlands Project “The Wildlands Project” which has the purpose of providing corridors from north to south in North America.

These corridors will link existing reserves and surround both reserves and corridors with buffer zones that are hospitable to wild animals and plants. The time frame for achieving this goal is hundreds of years, given the political, social, and financial challenges.

Managing Gene Flow This involves considerable complexity as many issues must be addressed including:  Which individuals to translocate?  How many individuals should be translocated?  How often should translocation occur?  What are the source and recipient populations for translocation?  When should translocation begin and stop?

Answering these questions requires that the population be genetically monitored. Since there are so many variables to optimize, computer projections will often be required to define and redefine the required management. The objective is to identify a regime that maintains genetically viable populations with acceptable costs that fits within other management constraints.

Re-establishing Extinct Populations To maximize population sizes and minimize extinction risks, populations that have become extinct should be re-established from extant populations, if the habitat can still support the species. Which populations should be The important questions is “Which populations should be used to re-establish extinct populations? used to re-establish extinct populations?” To minimize inbreeding and maximize genetic diversity, the re-founding population should be sampled from most, or all, extant populations.

However, where there is evidence of adaptive genetic differentiation among extant populations, as is common in many plant species, the translocated individuals should normally come from populations most likely to be best adapted to the reintroduced habitat. This is frequently the geographically closest population. Care should be taken when island populations are being considered as source populations for translocation as they typically have low genetic variation and are inbred.

Genetic diversity in populations available for restocking should be compared and the most diverse populations with the highest reproductive fitness, or a crossing among populations, chosen. Genetic Issues in Reserve Design Genetic Issues in Reserve Design: There are many biological, ecological, political, and genetic considerations to balance when considering the design of nature reserves.

It has been suggested that the following three steps need to be involved in the ecology and genetics of reserve design: 1. Identify target, or keystone species, whose loss would significantly decrease the value of biodiversity in the reserve. 2. Determine the minimum population size needed to guarantee a high probability of long-term survival for the species.

3. Using known populations densities of these species, estimate the area required to sustain minimum numbers. The genetic issues in reserve design are: Is the reserve large enough to support a genetically viable population viable population? Remember from previous discussions that N e is usually 0.1 that of N, thus to design a reserve to maintain an effective population size of several hundred, you would need several thousand individuals?

Is the species adapted to the habitat of the reserve? Should there be one large reserve, or several smaller reserves? This relates to the “Single Large vs. Several Small (SLOSS) reserves. In general, a single large reserve is more desirable from the genetic point of view, if there is a risk that populations in small reserves will become extinct (a likely scenario for many species).

However, protection against catastrophes dictates that more than one reserve is preferable, or even obligatory. The best compromise is to have more than one sizeable reserve, but to ensure that there is natural or artificial gene flow among them. In practice, the choice of reserves has often been a haphazard process, determined more by local politics, alternative land uses and the need for reserves to serve multipurposes, than biological principles.

Introgression and Hybridization Introgression is the flow of alleles from one species, or subspecies, to another. Typically, hybridization occurs when humans introduce exotic species into the range of rare species, or alter habitat so that previously isolated species are now in secondary contact. Introgression is a threat to the genetic integrity of a range of canid, duck, fish, plant, and other species.

Options for eliminating introgression include eliminating the introduced species, or translocating “pure” individuals into isolated regions or into captivity. Impacts of Harvesting Many species of wildlife and plants are harvested. This may alter effective population size, genetic diversity, and generation length. Usually, the effects are deleterious genetically.

For example, Ryman et al. (1981) showed that hunting moose and white-tailed deer would severely reduce genetic diversity within short periods. Hunting regimes reduced the effective population size by 64% to 79% in moose and 58% to 65% is deer, depending upon the hunting regime and assumptions made. Poaching has had a devastating effect on sex-ratio and reproductive rate in Asian elephants.

Many wild species are selectively harvested by humans who favor particular phenotypes within populations. These include elephants, rhinoceroses, deer, moose, fish, whales, crustaceans, forest trees, and many other plants. Such selective harvesting may result in selection pressure that change the phenotype of the species, conflicting with forces of natural selection and reducing the overall fitness of populations. For example, males with large antlers are favored prey of hunters.

This is expected to select for smaller antlers, conflicting with natural selection favoring large antlers in males. As harvested species often occur in large, though frequently declining numbers, an option is to preserve a proportion of the population from harvest. In this way, fully wild stock is maintained to introduce into harvested areas so that the genetic impacts of harvest are reduced.