1. Let‘s talk about ........ Thomas Geburek Department of Genetics
Federal Research Centre for Forests, Natural Hazards,
and Landscape (BFW)
Austria
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

2. Population Sizes, ESUs, MVP, PVP
Let‘s talk about
Population Sizes, ESUs, MVP, PVP
Thomas Geburek
Department of Genetics
Federal Research Centre for Forests, Natural Hazards,
and Landscape (BFW)
Austria
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

3. Adaptive Genetic Variance Effective Population Sizes
Extinction
Adaptive Genetic Variance
Effective Population Sizes
Heterozygosity
Transfer of FGR
MVP
SLOSS
ESU
Population Size
Fragmentation
Genetic Richness
Inbreeding
Sampling
ex situ
Bottleneck
in situ
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

4. Population and Metapopulation: some definitions
What is a population ?
What is a local population ?
What is a metapopulation ?
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

5. Hanski and Simberloff (1997)
Population and Metapopulation: some definitions
Population
Population a community of potentially interbreeding individuals at a given locality sharing a common gene pool.
Local population: “Population, subpopulation, deme”
Set of individuals that live in the same habitat patch and therefore interact with each other; most practically applied to “populations” living in such small patches that all individuals practically share a common environment and gene pool.
Johannsen (1903)
Hanski and Simberloff (1997)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

6. Population and Metapopulation: some definitions
“any assemblage of discrete local populations with migration among them”
Populations that are spatially structured into assemblages of local breeding populations with migration between them that affects local population dynamics, including the possibility of reestablishment following extinction
What is the difference to panmitic populations?
Hanski & Gilpin (1997)
Hanski & Simberloff (1997)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

7. Population and Metapopulation: some definitions
“any assemblage of discrete local populations with migration among them”
Populations that are spatially structured into assemblages of local breeding populations with migration between them that affects local population dynamics, including the possibility of reestablishment following extinction
What is the difference to panmitic populations?
Contrast with panmictic population where every individual has equal likelihood of interacting with every other one !
Hanski & Gilpin (1997)
Hanski & Simberloff (1997)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

8. Metapopulation: types
Levins’ metapopulation: “classical metapopulation”
A large network of similar small patches, with local dynamics occurring at a fast time scale; sometimes used to describe a system in which all local populations have a high risk of extinction
Mainland-island metapopulation: “Boorman-Levitt metapopulation”
System of habitat patches located within dispersal distance from a very large habitat patch where the local population never goes extinct (hence, M-I metapopulations never go extinct)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

9. Metapopulation: types
Harrison & Taylor (1997)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

10. Effective population size: three concepts
Different definitions depending on which aspect of the
polymorphism fluctuation we are interested in:
Inbreeding effective size  Change in inbreeding level
Variance effective size  Change in gene frequencies
Eigenvalue effective size  Change in heterozygosity level
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

11. Effective population size: definitions
The size of an ideal population for which we would have a fluctuation of polymorphism (rate of genetic diversity loss or rate of genetic drift) equivalent to that of a natural population:
Why does a census population differ normally from an effective population size?
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

12. Effective population size: definitions
The size of an ideal population for which we would have a fluctuation of polymorphism (rate of genetic diversity loss or rate of genetic drift) equivalent to that of a natural population:
not equal to the census number N
influenced by the number of breeding individuals in a population
time fluctuations of the population size (seasonal, climatic change) and sex ratio
variance of the number of offspring (polygyny, polyandry, sexual selection)
inbreeding
overlapping generations
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

13. Effective population size: unequal sex ratio
 Inbreeding effective size
4 Nm Nf
Ne =
Nm + Nf
Compare census and effective population size of this Training Workshop!
Training Workshop on Forest Biodiversity, June 2006, Kuala Lumpur, Malaysia

14. Effective population size: unequal sex ratio
 Inbreeding effective size
4 Nm Nf
Ne =
Nm + Nf
Malaysian example:
Garcinia scortechinii tended towards femalenees in a censused 25 ha area in the Pasoh Forest Reserve (West Malaysia). No males recorded, however 68 % of the adult trees fruited (Thomas 1997).
Sexual function S = 1.0
Ne = 0 !
Training Workshop on Forest Biodiversity, June 2006, Kuala Lumpur, Malaysia

15. Effective population size: unequal sex ratio
 Inbreeding effective size
Effective size of a dioecious population of
census size 100 as a function of the number of males in the population
Effective sizes of a dioecious population for different sex-ratios
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

16. Effective population size: size fluctuations
 variance effective size
Var(k)=0
all breeding individuals produce an identical number of offspring
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

17. Effective population size: size fluctuations
 eigenvalue effective size
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

18. Effective neighborhood size
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

19. A = 4 π (δ /2 + δ ) Effective neighborhood size
General definition extended to the case of monoecious dispersing plants by pollen and seeds:
A = 4 π (δ /2 + δ ) 2 2 p s
Levin & Kester (1968)
Quercus petraea (isozymes) A = 15.2 ha
(SSR) A = 19.3 ha
Querucs robur (SSR) A = 12.0 ha
Le Corre et al. (1998)
Streiff (1998)
Streiff et al.(1999)
Genetic neigbhourhood sizes approx trees
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

20. Minimum viable population (MVP): definition
Thomas Geburek, Department of Genetics, Austria

21. How large?
Three major components must be considered in answering this question:
Is the population large enough to avoid inbreeding depression?
(2) Is there sufficient genetic diversity to retain evolutionary potential ( Allee effect)
(3) Is the population large enough to avoid accumulating new deleterious mutations?
How would you define MVP ?

22. Minimum viable population: definition
one that meets ‘the minimum conditions for the long-term persistence and adaptation of a species or population in a given place’ .
theoretically sufficiently large to protect against extinctions caused by harmful and unpredictable genetic, demographic or environmental factors over a given period of time (generally expressed in hundreds of years).
Soulé (1987)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

23. Minimum viable population: checklist
The environment including 'worst-case' eventualities that affect the viability of the population:
Habitat quality including herbivore pressure (game browsing etc.), insect gradations and fungal epidemics.
Habitat quantity available for the target species.
Disturbance regime (fire, avalanches, torrents, etc)
Population size, structure and fitness are the field of dynamic interactions between a population and its environment.
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

24. Minimum viable population: checklist
The physical, chemical amd general biological properties of a population:
Physiology, morphology and disease resistance.
Mode of reproduction.
Adaptedness to the given environment (ability to survive and reproduce)
Microspatial distribution of trees pollen dispersal, mating
Macrospatial distribution
Ability to occupy the given habitat and to migrate into others
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

25. Minimum viable population: checklist
The environment including 'worst-case' eventualities that affect the viability of the population (continued):
The age structure of the individual population determines the fluctuations of population size. In addition, the totality of genetic resources of a species should have an age structure in order to have reproductive material continuously available for use, and for safety considerations.
Intrinsic rate of increase and its spatial variation.
Sex ratio. In dioecious species the sex ratio is among the determinants of the completeness of pollination and the evenness of seed distribution. It varies also within species.
Dynamics of spatial distribution (size and distribution of patches).
Genetic variation (proportion and number of polymorphic gene loci and the numbers of their alleles). Pertinent information exists mainly about neutral marker loci.
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

26. Minimum viable population: checklist
The environment including 'worst-case' eventualities that affect the viability of the population (continued):
Heterozygosity. The previous and this term are often used as synonyms. It is true that without genetic variation there is no heterozygosity. However, heterozygosity is a parameter of the genotypic structure and does not directly measure genic variation.
Adaptability. Genetic variation is considered to be the sole basis of adaptability. Environmental degradation challenges adaptational processes in tree populations.
Spatial genetic structure. Restrictions on the transport distances of effective pollen and viable seed imply the development of spatial genetic structures. This is eventually enhanced or blurred by viability selection.
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

27. Discussion of the 50/500 rule of thumb
No finite population is immune from eventual inbreeding depression
Generally we do not know precisely how large population must be to avoid meaningful inbreeding depression.
Pragmatically the IUCN scheme for categorization extinction risk is set as
50 adults critically endandered
250 adults endangered
1000 adults  vulnerable
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

28. Effective population sizes of approx
Effective population sizes of approx have been suggested as necessary to maintain short-term evolutionary potential.
Populations with Ne less than 500 are not doomed to immediate extinction, but will became increasingly vulnerable with time.
Wild populations often require a census size about 10 times larger than Ne .
Effective population sizes of 10,000 to 100,000 are required to retain single-locus diversity due to the balance between mutation and drift.
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

29. How to prioritize objectively conservation units?
Towards a unified concept for defining conservation units:
„Selective Environmental Neighborhoods“ (SEN)
(sensu Brandon)
„Evolutionary Signifcant Units“ (ESU)
(sensu Ryder, Waples, Crandall et al. among others)
first concept appeared in the eighties
developed to provide an objective approach to prioritizing units for protection below the species level
concept has been frequently moulded
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

30. Evolutionary Signifcant Unit (ESU) (sensu Crandall et al.)
(1) Ecological exchangeability
Individuals can be moved between populations and can occupy the same ecological niche
(2) Genetic exchangeability
Individuals are genetically exchangeable if there is ample gene flow among populations.
Unique alleles or low gene flow estimates (effective number of migrants per generation (Nm) <1) are indicative fo non exchangeability.
Crandall et al. (2000)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

31. Extinction: definition
Reproductive failure or death of the last individuals of a population or species.
What is causing extinctions?
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

32. Extinction: definition
Reproductive failure or death of the last individuals of a population or species. Caused by
(1) Demographic stochasticity
(2) Environmental stochasticity including catastrophes
(3) Genetic stochasticity
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

33. Extinction: demographic, environmental and genetical stochasticity
(1) Demographic stochasticity
Random fluctuation of population parameters such as distribution of age classes or sex ratios
Individual of any age have specific rates of survival and reproduction
 Chance variation in individual birth and death
(2) Environmental stochasticity
Induced by temporal changes of rates of survival and reproduction
Fires, damages by wind and snow, drought periods, large-scale cuttings of forests, insects graduation, outbreaks of parasites
 Random series of environmental changes
(3) Genetic stochasticity
Main source is finite population size
Drift effects including bottleneck and founder effects
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

34. Population Viability Analysis (PVA): definition
Assessing the likelihood that a population will persist over time, estimation of extinction probabilities by analyses that incorporate identifiable threats to population survival in to models of the extinction process.
Will a population fail or prosper in response to specific circumstances?
What is the risk of extinction for a population over a specific time, under a given set of circumstances?
Based on a model that relates a dependent variable (i.e. N) to the independent variables that influence it (weather, mortality, etc.), this relationship is mediated through parameters (i.e. survival rates, reproductive rates)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

35. Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

36. Population Viability Analysis (PVA) How do we do a PVA?
(1) Construct a mathematical model using the following data:
Average mortality rates
Average recruitment rates
Current age distribution
Current size
(2) Add stochasticity to the model
Allow model elements to vary at random between their observed
range of annual values
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

37. Population Viability Analysis (PVA): Benefits
Simulations of individual populations can be run using this random variation to determine the probability of population extinction within a certain period of time or the mean time to extinction.
Can determine which parameter or combination of parameters most influences extinction probabilities
Management regimes that affect population parameters can then be developed and analyzed
Simulations of the impact of this management regime could be compared with the original population model to determine how it affects the probability that the population will persist in the future – can evaluate the effectiveness of management efforts
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

38. Population Viability Analysis (PVA): Problems
Different definitions – not restricted to a mathematical model, but should be
Estimating parameters – totally dependent upon field data which is not always available (the more data, the better the analysis)
Can’t diagnose the cause of decline, or prescribe a remedy for it
Level of uncertainty may be large
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia

39. By now you know
.....
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia