
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. Let‘s talk about Population Sizes, ESUs, MVP, PVP. Thomas Geburek
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Thomas Geburek
Department of Genetics
Federal Research Centre for Forests, Natural Hazards,
and Landscape (BFW)
Austria
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
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
Adaptive Genetic Variance
Effective Population Sizes
Heterozygosity
Transfer of FGR
MVP
SLOSS
Population Size
ESU
Fragmentation
Genetic Richness
Inbreeding
Sampling
ex situ
Bottleneck
in situ
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
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
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
Population and Metapopulation: some definitions
Metapopulation
“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
Population and Metapopulation: some definitions
Metapopulation
“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
Levins’ metapopulation: “classical metapopulation”
Mainland-island metapopulation: “Boorman-Levitt metapopulation”
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
Harrison & Taylor (1997)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
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
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
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
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
Effective population size: unequal sex ratio
Inbreeding effective size
4 Nm Nf
Ne=
Nm + Nf
Malaysian example:
Garciniascortechinii 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
Training Workshop on Forest Biodiversity, June 2006, Kuala Lumpur, Malaysia
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
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
Effective population size: size fluctuations
eigenvalue effective size
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
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. 1200 - 4000 trees
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
Minimum viable population (MVP): definition
Thomas Geburek, Department of Genetics, Austria
How would you define MVP ?
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
Minimum viable population: checklist
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
Minimum viable population: checklist
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
Minimum viable population: checklist
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
Minimum viable population: checklist
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
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
Effective population sizes of approx. 500 - 5000 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
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)
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
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
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
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
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
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
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
Population Viability Analysis (PVA): Benefits
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia
Population Viability Analysis (PVA): Problems
Training Workshop on Forest Biodiversity, Kuala Lumpur, Malaysia