RESOURCE NOTES NO. 35 DATE 08/01/00 maintain sufficient genetic diversity DEFINITION: Metapopulation refers Summary within these populations. to two or more local breeding popula- tions which are linked to one another by Recommendations- DISCUSSION: Reproductive capac- dispersal activities of individual animals. ity is, to a large degree, dictated by These populations may have unique BLM Wild Horse the genetic fitness of a population. demographic features (birth and death Generally speaking, the higher the rates) but ultimately may share some and Burro level of genetic diversity, within the genetic material if interbreeding is herd, the greater its long-term repro- occurring between individuals. This Wild Horse and Burro Program Population ductive capacity. Inbreeding, random sharing of genetic material may act to matings (genetic drift), and/or envi- enhance genetic diversity within par- Viability Forum, ronmental catastrophes can all lead to ticipating herds, and as such, these the loss of genetic diversity within the populations should be evaluated as April 21, 1999 population. In most herds, though, one larger metapopulation. by Linda Coates-Markle, genetic resources will tend to be lost Montana/Dakotas Wild Horse slowly over periods of many generations DISCUSSION: A complete popula- (~10 years/generation), and there is tion census of each herd management and Burro Specialist, little imminent risk of inbreeding or area is unrealistic, especially for the larg- Bureau of Land Management, population extinction. Potential nega- er populations (>200 total census Montana State Office tive consequences of reduced diversity, size). However, population size can however, may include reduced foal pro- and should be estimated using reliable duction and survival, as well as reduced scientific techniques. These survey The final Note in a series adult fitness and noted physical defor- techniques are under continual revision of 13, Session 4 mities. Smaller, isolated populations and BLM continues to participate in (<200 total census size) are particularly these research efforts. On a more critical RECOMMENDATION #1: vulnerable when the number of ani- level, however, is the determination of BLM should carefully consider its man- mals participating in breeding drops size of the many smaller populations date (The Wild Free-Roaming Horse below a minimum needed level. This (<200 total census size) over which and Burro Act) with respect to long- minimum level can be calculated and BLM has responsibility. Available data term genetic viability of populations of is different for each population (see indicates that almost 70% of the man- wild horses and burros. subsequent recommendations). aged herds have AMLs (appropriate management levels) set at 150 animals EXISTING POLICY: BLM regula- RECOMMENDATION #2: or less. In fact, almost 40% of the herds tions and policy state that wild horses BLM should continue to use (and in Nevada, Utah, Wyoming, Colorado, and burros Rangeshall be managed as viable, improve upon) defensible scientific aer- and Arizona (71 out of 177 total self-sustaining populations of healthy ial and/or ground survey techniques in HMAs) are indicated to have popula- animals in balance with other multiple census activities for all managed wild tion sizes of less than 50 animals. There uses and the productive capacity of horse and burro herds. In order to fully is a real possibility that some of these their habitat (CFR 4700.0-6). evaluate genetic viability issues, popula- populations will be unable to maintain tions which participate in a measurable self-sustaining reproductive ability, over the long term, unless there is a natural DEFINITION: Self-sustaining refers level of natural ingress or egress activity or management induced influx of to the process whereby established and which are, in reality, a component genetic information from neighboring populations are able to persist and of larger metapopulations, should be herds. An exchange of only 2 to 3 breed- successfully produce viable offspring identified, and the genetic impact of ing age animals (specifically females), which shall, in turn, produce viable this activity should be estimated. every 10 years, is often sufficient to offspring, and so on over the long term. maintain genetic diversity within a given The absolute size which a population EXISTING POLICY: BLM regula- herd. Estimates of existing genetic diver- must attain to achieve a self sustaining tions and policy state that HMAs sity can be calculated for each wild horse condition varies based on the demo- should be inventoried and monitored and burro population (see subsequent graphic and sociological features of the for population size, animal distribu- recommendations). herd (and adjoining herds), and these tion, herd health and condition and aspects should be evaluated on a case by habitat characteristics at least every 4 case basis. In many cases it is not neces- years (CFR 4710.2). As such, BLM is RECOMMENDATION #3: sary that populations be isolated genetic required to provide reliable estimates of BLM should establish baseline genetic units, but both naturally-occurring and population size and distribution with- diversity information for each popula- management-induced ingress and egress in each herd management area on a tion over which it has management activity can be considered, in order to regular interval. responsibility. Range EXISTING POLICY: BLM regula- a result, a comparison of genetic viabil- DISCUSSION: Once baseline genetic tions and policy state that HMAs ity levels in the tested population can data has been established, the main should be inventoried and monitored be made to existing information from focus of genetic management, especial- for population size, animal distribu- over 100 domestic and wild horse ly for the smaller populations (<200 tion, herd health and condition and populations representing different total census size), becomes the attempt habitat characteristics at least every 4 herd sizes and demographic back- to preserve as much of the existing years (CFR 4710.2). Furthermore, the grounds. genetic diversity as possible. Establishing purpose of monitoring is to collect a genetic conservation goal will require data necessary to evaluate progress (or re-testing of herd diversity on at least lack thereof) in achieving the objectives RECOMMENDATION #4: a five-year cycle, with subsequent eval- of management. Within the context BLM should establish a realistic man- uations of the potential impact of of wild horse and burro populations, agement goal for maintenance of management decisions (including the ability to maintain the quality of genetic diversity within all managed the establishment and/or revision of “reproductively self sustaining” is populations. Previous wildlife conser- appropriate management levels) on required. This can primarily be vation research, and current efforts that diversity. Management may need accomplished through evaluation and with wild horses, suggest management to evaluate ways to introduce genetic the maintenance of an acceptable level should allow for a 90% probability of material into a herd which appears of genetic diversity within the popu- maintaining at least 90% of the exist- genetically deficient in order to be lation over the long term. ing population diversity over the next self-sustaining over the long-term (see 200 years. Existing diversity should be subsequent recommendations). sufficient to ensure a self-sustaining Baseline genetic data can also be incor- DEFINITION: Establishing baseline (see earlier definition) reproductive porated into PVA (population viability genetic diversity, for a wild horse popu- capacity within the herd. analysis) models, which attempt to lation, often refers to typing up to 29 predict the impact of management genetic marker systems from a sample of EXISTING POLICY: BLM regula- decisions (as well as environmental cat- individual animals (~25 individuals or tions and policy state that wild horses astrophes) on existing diversity levels. up to 25% of the population) within a and burros shall be managed as viable, Most models require reasonably accu- specific herd. Traditionally, these marker self-sustaining populations of healthy rate data in terms of age class foaling systems have included blood group and animals in balance with other multiple and mortality rates, as well as individ- biochemical systems, and have required uses and the productive capacity of ual genetic information. As such, the fresh blood samples. These systems their habitat (CFR 4700.0-6). By defi- means to collect accurate data neces- were originally developed for verifying nition this requires BLM to manage to sary for a genetically-based PVA, for parentage or founder animals within a allow established populations to suc- most herds, is probably unavailable herd. Analysis of genetic diversity, how- cessfully produce viable offspring at the present time. ever, can also be done through the use which shall, in turn, produce viable of DNA genetic marker systems, and offspring, and so on over the long direct testing can utilize almost any bod- RECOMMENDATION #5: term. This suggests that management ily product including hair or even feces. BLM should, in its efforts to evaluate monitor levels of genetic diversity Only DNA marker analysis can be used the genetic diversity and self sustaining within the population in order to for burros, however, due to the very nature of managed herds, estimate the mitigate the effects of genetic drift limited variation