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Human aspects
Landscape
Ecosystem
Population
Individual Community
Human aspects demands
ecology to be a predictive science
Conserve what?
Biodiversity
One species/population at a time
What is a species or a population?
Biological, Evolutionary, Ecological
>15,000 species are listed as threatened with
extinction worldwide by IUCN’s Red List
International Union for Conservation of Nature and Natural
Resources
RedList conservation status
Least concerned
Near threatened
Vulnerable
Endangered
Critically endangered
Extinct
Monitoring
Restoration
Conservation biology
Ecology
Social science
Evolution
Population viability analysis
(PVA)
Population viability
PVA
The probability of continued
existence of a population, p(r>0) = ?
The quantitative models to predict
population extinction risks, p(r<0) =
1-p(r>0)
PVA = Population model
deterministic
stochastic
Stochasticity 1
Demographic stochasticity:
Unpredictable changes in a population’s
demography (how many individuals die,
how many reproduce, etc.) caused by the
randomness of individual fates.
Stochasticity 1
Demographic stochasticity:
Nt = Nt-1 x (e)r[1-(Nt-1/K) + ɛ(t)]
r is not a constant but a result of chance event
ri = f(b) - g(d), i = 1,2,3,…,Nt-1
Stochasticity 1
Demographic stochasticity: r = ?
Individual
1
2
3
4
5
b
d
ri
Stochasticity 2
Environmental stochasticity:
Unpredictable changes in average
demographic rates of a population, caused
by vacillations in weather, food, predators,
or other biotic and abiotic forces.
Stochasticity 2
Environmental stochasticity:
Nt = Nt-1 x (e)r[1-(Nt-1/K) + ɛ(t)]
r is a constant at any given time but is
adjusted by K and ɛ(t)
rt = r[1-(Nt-1/K) + ɛ(t)]
Stochasticity 3
Genetic stochasticity:
Unpredictable changes in gene frequencies
as a result of neutral processes such as
genetic drift.
Why would changes in gene frequencies affect
population growth?
Stochasticity 3
Genetic stochasticity:
1
0.75
0.5
0.25
A/B
0
A
B
birth
b
d
r
50/50 1/1 0.2/0.8 0.5
0/100 1/1 0.2/0.8 0.2
Are these stochastic process?
Higher temperature due to climate change
increases disease risk and mortality?
Higher temperature due to climate change
select for genotypes with weak immunity?
Higher temperature due to climate change
changes life history to early reproduction?
Stochasticity in PVA
Stochasticity
Population size
Spatial scale
Data
requirement
Environmental
Any
All
Higher
Demographic
Small
Local
Lower
Genetic
Small
Local
Higher
Major Categories of PVA
Census- or count-based
Stage-structured
Spatial-structured
Individually based
Census- or count-based PVA
Nt = λ x (Nt-1)
λ = (Nt / Nt-1)
ln(λ) = ln (Nt / Nt-1)
mean[ln(λ)] = expected population growth
Var[ln(λ)] = year-to-year variation in
population growth
Stage-structured PVA
Population growth rate is a matrix of stagestructured fecundity and survival:
f and p: fecundity and survival, both can be
modeled using probability distribution
PVA models
Model
Stochasticity
Technique
Census
Var (population growth rate)
Parametric
Stage-structured
Probability distribution of
survival and fecundity
Parametric
Probability distribution of patch
Spatial-structured
colonization and extinction
Parametric
Chance event of survival,
reproduction and movement of
each individual
Simulation
Individually based
Typical output of PVA
Expected population growth rate
Future population size
Extinction risk
Quasiextinction threshold
Sensitivity
Quasiextinction threshold (Nqe)
The minimum number of individuals
below which a population is likely to be
critically and immediately imperiled.
Example: Sensitivity in PVA
Atlantic Loggerhead Sea Turtle Caretta caretta
By ukanda
Creative commons 2.0
Example: Sensitivity in PVA
Two major threats to the loggerhead:
loss and degradation of nesting habitat
and direct harm to eggs and hatchlings
drowning of individuals in the nets of
fishing boats trawling for shrimp.
Example: Sensitivity in PVA
Crouse DL et al. 1987. A stage-based
population model for loggerhead sea turtles
and implications for conservation. Ecology
68: 1412–1423.
Crowder LB et al. 1994. Predicting the
impact of turtle excluder devices on
loggerhead sea turtle populations.
Ecological Applications, 4, 437-445.
Example: Sensitivity in PVA
Two major threats to the Loggerhead:
loss and degradation of nesting habitat
and direct harm to eggs and hatchlings
drowning of individuals in the nets of
fishing boats trawling for shrimp.
Turtle Excluder Device (TED)
NOAA Fisheries
Example: Spatial-structured PVA
Red-cockaded woodpecker
(Picoides borealis)
By Patrick Coin, Creative Common 2.5
Example: Spatial-structured PVA
Major threat to red-cockaded woodpecker
low breeding success limited by existing
and slow generating natural tree holes
Example: Spatial-structured PVA
Letcher, BH et al. 1998. An individualbased, spatially-explicit simulation model of
the population dynamics of the endangered
red-cockaded woodpecker, Picoides borealis.
Biological Conservation, 86, 1-14.
The aggregation and number of territories (tree
holes) to ensure population viability
Population Viability Management (PVM)
Island foxes (Urocyon littoralis)
Population Viability Management (PVM)
Major threat to the island foxes:
Predation by golden eagle
To conserve the fox,
the best management
is to remove eagles,
which is extremely
expensive
Population Viability Management (PVM)
Bakker, V. J., & Doak, D. F. 2008. Population
viability management: ecological standards to guide
adaptive management for rare species. Frontiers in
Ecology and the Environment, 7, 158-165.
Is there a viability analysis for
community or ecosystem?
Population viability analysis targets a clear
parameter: extinction risk
Community and ecosystem lack a
definable modeling target