Principle - Ecological

Criterion- Reorganized under S: Native species diversity is maintained.

Original Indicator –– Population sizes and demographic structures do not show significant changes, and demographic and ecological critical life –cycle stages continue to be represented.

Revised indicator - Populations of indigenous species are likely to persist.

Box B: Definition:

CIFOR Indicator –– Population sizes and demographic structures do not show significant changes, and demographic and ecological critical life –cycle stages continue to be represented.

Although not clear in the CIFOR documentation, we interpreted this indicator as referring to the maintenance of viable population of native species (indigenous species refers to all species, both plant and animal). The likelihood of persistence of populations can be estimated through set of calculations called a population viability analysis. Population viability analysis is described as a systems approach that emphasizes the interaction of factors and sees viability in terms of a probability. It incorporates both an assessment of minimum viable populations and minimum viable areas for those populations.

Box D: Applicability to Different Landowners. Explain any differences:

Using a model of sustainability, land managers work to ensure ecosystem structures and functions are maintained. However, even with the best of intentions, landowners cannot be responsible for the persistence of all indigenous species on their lands. Many species indigenous species require very large home ranges and occur in populations that cover many thousands of square kilometers (i.e. grizzly bear, wolverine). Other species are migratory and might spend part of the year in distant locations (i.e. neo-tropical migrant songbirds or Chinook salmon). The landowner can manage for part of such species’ requirements. To ensure species survival, landowners can cooperate to plan for the needs of such wide-ranging species. Planning must occur for species with regional needs and species with distinct seasonal needs such as long distance migrants. Without such planning and cooperation, many such species will not persist.

Box E: Overlap:

CCFM 1.2.2 – Population levels and changes over time for selected species and species guilds.

CCFM 5.1.3 - Animal population trends for selected species of economic importance.

CCFM 5.1.5 - Availability of habitat for selected wildlife species of economic importance.

Notes:

The concept of viable populations applies to all indigenous species. Different species populations occupy different spatial scales, from 1 m² up to continental migrants. However the Boise study area, at about 1.8 million hectares, would contain the complete like history needs of the majority of the species. Over species would have be part of meta-populations that exist throughout the intermountain west (i.e. wolverine) or through the Americas (i.e. yellow warbler).

Notes: Population viability analysis is inherently predictive, calculating the probability of persistence of a given population for a given period of time.

Notes: This indicator predicts the probability of survival of one ecosystem component.

Box I: Underlying Concepts:

The question of population viability has been examined by two, often exclusive, approaches. Community ecologists have focused on minimum areas for system viability, building on the contributions of island biogeography theory. Conversely, population biologists have focused on minimum population sizes or densities. According to Soulé (1987), these divergent views have come together with the realization that the most pragmatic way to define system viability is to do so in terms of critical or keystone species within the system. Viability analysis is described as a systems approach that emphasizes the interaction of factors and sees viability in terms of a probability. It incorporates both an assessment of minimum viable populations and minimum viable areas for those populations.

The concept of viability has been the subject of debate because of inherent uncertainties in its definition. First, there is the question of time. Is the population viable in the long term or short term? Second, should the analysis of viability for a target population include provisions for catastrophes, such as epidemics? There is also the question of genetic drift in small populations and how much is acceptable. The biology of the species in question also must be taken into account. How patchy is the distribution? What is its sexual behavior? Does one male dominate and mate with several females? To what types of stochastic uncertainty is the population subject? These questions all interact, resulting in a high level of complexity. Today, the most widely accepted approach to this complexity is to conduct a viability analysis, which is described as a systems approach that emphasizes the interaction of factors and sees viability in terms of a probability.

Definitions of viable population size involve a probability of survival for a given number of years. Compounding the issue is the fact that the eventual extinction of all species is certain. Certainly the fossil record supports that conclusion. A common definition format used in conservation biology for minimum viable population size is the size of population X which guarantees a Y% probability of survival for Z years. The most commonly used values for the probability are 95 or 99%. The most commonly used time frames are 100 and 1000 years. It is important to note that the calculation of a minimum viable population size depends enormously on the chosen probability and persistence times. It is also important to note that such definitions are completely different from short term rules like the rule of 50 or the 1% rule that have been used in population biology (Lavaca and Hughes, 1984). Such rules of thumb have suggested that an effective population size, meaning an interbreeding population, should be 50 for short-term conservation and 500 for long-term conservation (Franklin, 1980).

It is important to stress that there is no magic number for population viability, that the question is one of probability. Although each situation is unique to a site, the same approach can easily be used in different situations. There are fixed lower limits that a population should never get below and these numbers are set by genetics and the need to maintain heterozygosity. Such fixed limits are usually below the numbers required to ensure population persistence on the basis of changes brought by stochastic elements (i.e. low recruitment caused by drought).

The susceptibility of a given species to extinction is a function of many factors, the most important being body size, age at first reproduction, birth interval and susceptibility to both slow and catastrophic change. For example, large-bodied, long-lived species such as redwood trees have a low rate of turnover (extinction and recolonization of a patch) and are more susceptible to extinction than small, short-lived species like annual plants (Goodman, 1987).

Box J: Relevance to Sustainable/Unsustainable Management:

Maintenance of viable populations of native species is a fundamental part of maintaining ecological integrity. As Aldo Leopold once put it "The first rule of intelligent tinkering is to keep all the parts".

Box K: Measurement Methods:

The data required for a population viability analysis are complex and are listed below:

1. Population dynamics including the basic measures like natality, mortality, age at first reproduction, total reproductive output, immigration and emigration.

2. Population genetics, especially the degree of heterozygosity, the rate of genetic drift, and the expected rate of gene flow into the population. Heterozygosity is a measure of genetic diversity, specifically the proportion of genes that have different alleles. Genetic drift is the variation in gene frequency from one generation to the next due to change fluctuation.

3. The susceptibility of the population to catastrophe.

4. The amount of environmental variation that the population is subjected to, including the degree of randomness and stochasticity.

5. The "metapopulation structure" which refers to the population of populations. With a large metapopulation, the probability of extinction decreases because of recolonization and protection from random variation and catastrophe.

6. The fragmentation of the population, including measures of patchiness and uniformity of scale.
7. The suitability of the environment to support a given density of the species.

Population viability analysis cannot be done on all species. Because of the data required, population viability is generally only done on select indicator species. Such species are chosen because they (1) are at risk in the management area, (2) are of particular economic of social value or (3) are considered to be "umbrella" species that indicate the survival of a number of other species.

A range of selection criteria for different categories of indicator species is listed below (after Woodley, 1992):

1. Species vulnerable to identifiable indirect or distant threats such as acid precipitation or climatic shifts.

2. Species vulnerable to identifiable direct or local threats such as disturbance from visitor use.

3. Rare species of all kinds. (with defensible definitions of rarity according to national, state or provincial designations).

4. Controlling species such as summit predators or keystone species.

5. Old-growth or non-disturbance species.

6. K-selected species such as extreme habitat specialists or species with low fecundity or low capability for compensatory recruitment.

7. Species with large body size.

8. Exotic or non-native species that are successfully living and reproducing in a given ecosystems.
9. Accumulator species or those that have a tendency to accumulate toxins, such as filter-feeding bivalves.
10. Species subject to legal harvest.

There are various software programs that can be used to assess populations viability (see Lacy, 1993; Possingham and Davies,1995; Lindenmayer et al., 1995). These are combined with habitat suitability models and habitat dynamic models to assess persistence. There is no a single specific methodology for assessing population viability. It is best described as an approach with a set of useful tools.

Box L: Data Required:

See box K – Data needs depend on the species in question. In general there is a requirement for existing population data, age specific mortality and natality rates, emigration and immigration rates, breeding strategies. There is also a need for habitat suitability measures and the dynamics of the environment.

Box M: Data Used for the North American Test:

Population viability analysis’s have been conducted for a number of species in the Boise study area based on years of comprehensive field work. The Boise National Forest has selected for several species for population viability analysis including elk, mule deer, red-backed vole, meadow vole, Pileated woodpecker, mountain chickadee and yellow warbler. Each of the species was chosen to be representative of a particular habitat type (i.e. redbacked vole for old growth habitat) or habitat element (i.e. Pileated woodpecker for large snags). There has also be considerable research done on fish, including native trout (cutthroat, rainbow and bull), anadromous fish (Chinook salmon and Steelhead trout).

Box N: Example Results:

The following results were taken from the Boise National Forest, presented in the Land and Resource Management Plan. Viability is calculated differently for different species. Elk uses the elk habitat effectiveness model scores as a unit of measure, based on a calculated minimum viable population of 1225 animals. Mule deer uses the area of winter range based on a calculated minimum viable population of 1720 wintering animals. The other 10 species are presented in a more standard format, given as the number of acres of habitat (in thousands) required to ensure a viable population. Calculations are for minimum viable acres, existing acres and potential acres on the landscape.

The different approaches to viability analysis shown above illustrate that population viability analysis is not a specific technique. Rather such analysis represents a approach with a number a powerful tools that can be used in the approach. At present, the other landowners in the study area do not conduct population viability analysis, although Boise Cascade is developing minimum habitat objectives for songbirds and the State of Idaho has minimum targets for hunted species.

Box O: Assessing the Practicality:

It is difficult to conduct population viability analysis. They require very detailed data sets as well as sophisticated computer models. However such data sets and models exist for many north American species and there are many published case studies. Population viability assessment is complicated but certainly operational. There have been assessments for a wide variety of species done all over the world. In addition there are excellent, low cost software programs available to assist in preparing viability analysis such as the VORTEX program available from the Captive Breeding Specialist Group of the Species Survival Commission of the World Conservation Union (IUCN). (http://pw1.netcom.com/~rlacy/vortex.html).

Box P: Assessing the Information Value:

Population viability analysis relies on the use of indicator species and the choice of individual species must be carefully done or the results may be misleading. Many cautions have been issued over the use of indicator species (Landres et al., 1988). The cause and effect relationships suggested by indicator species may be misleading. For example the reduced clutch and fledgling success in great white herons was thought to indicate "poor habitat quality" of a shallow estuary in Florida. While this may be so, there are many other equally valid hypotheses for the same observations. There are other difficulties in the application of information from indicator species. Management of an area for an indicator may preserve only those environmental conditions needed by the species, ignoring ecological processes and resources needed by other species. No single biological indicator or indicator species has yet been found that will provide all the information necessary to interpret the behavior of an ecological system. Ideally, chosen indicators should be hypersensitive to stress, have ubiquitous natural distribution, be easy to collect and assay, and be a population that is not harmed by sampling for assay purposes. In addition, the ideal biological indicator should not die out easily as stress progresses, but should show response tiers.

The Boise National Forest’s use of several indicator species representative of a range of habitat types is a good model. It is comprehensive and provides an excellent synthesis of biological data that has high information value. Is also demonstrates the need to plan for viability of large home range or migratory species with a number of other landowners.

Box Q: Overall assessment

Accepted with major revision -

The use of population viability analysis was not suggested in either the CIFOR of CCFM indicator sets. This is surprising considering the strength of the available tools and the number of successful viability analysis done worldwide. We rewrote the indicator in explicitly incorporate population viability as the "likelihood of persistence".

Box R: Did you rewrite or revise to a new indicator. If so what?

Revised indicator - Populations of indigenous species are likely to persist.

Box S: References:

• Franklin, I.R. (1980). Evolutionary change in small populations. In. M.E. Soulé, and B.A. Wilcox (eds.) Conservation Biology: An Evolutionary-Ecological Perspective. Sunderland, Mass.: Sinauer, pp.135-149.
• Goodman, D. (1987). The demography of chance extinction. In. M.E. Soulé, (ed.) Viable Populations for Conservation. New York: Cambridge University Press. p 11-35.
• Lacy, R.C. 1993. VORTEX: A computer simulation model for Population Viability Analysis. Wildlife Research 20:45-65.
• Landres, Peter B., Verner J., and Thomas, J.W. (1988). Ecological uses of vertebrate indicator species. Conservation Biology 2(4): 316-28.
• Lavaca, Jerry and Hughes, Jeff. (1984). Determining minimum viable population levels. Wild. Soc. Bull. 12:370-376.
• Lindenmayer, D.B., M.A. Burgman, H.R. Akcakaya, R.C. Lacy, and H.P. Possingham. 1995. A review of the generic computer programs ALEX, RAMAS/space and VORTEX for modelling the viability of wildlife populations. Ecological Modelling 82:161-174.
• Possingham, H. P. and Davies, I. 1995. ALEX: A population viability analysis model for spatially structured populations. Biological Conservation 73:143-150.
• Soulé, Michael E. (ed.) (1987) Viable Populations for Conservation. Cambridge: Cambridge University Press, 189 pp.
• Woodley, S. J. and John Theberge. 1992. Monitoring for ecosystem integrity in Canadian National Parks. In: Willison, Marten J.H., Soren Bondrup-Neilson, Clifford Drysdale, Tom Herman, Neil W.P. Munro and Tom Pollack (eds.). Science and the Management of Protected Areas. Elsevier Press, Amsterdam.