BISC530: Biology Conservation Kedong Yin

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BISC530 Biology ConservationKedong Yin

• Introduction
• Habitat fragmentation
• Demographic Processes on heterogeneous
  landscapes Metapopulation dynamics

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Demographic Processes Population Dynamics on
Heterogeneous Landscape

1. What is population demography?
2. Mechanisms of population regulation
3. Habitat-specific demography
4. Population viability analysis
5. The landscape approach

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1. What is population demography?
The study of population fluctuations due to
birth, immigration, death, emigration (BIDE)
population structure such as age structure, sex
ratio and life history. BIDE Population
structure age and sex ratio life history (e.g.
insects, fish)
Birth
Popul. Size Structure
Emigration
Immigration
Death
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6
1945
1985
1940
Years
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Hong Kong Age Structure in 1998
Age
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Hong Kong Sex Ratio
Age
35
0
Male
Female
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District
81
86
91
81-86
86-91
81-91
Tuen Mun
Sha Tin
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Seal Population changes on two islands occupied
by US Coastal Guard Juvenile survival is
important in conserving seal populations
Tern Island
Coastal Guard in
Coastal Guard out
Green Island
Number of Seals
1980
1960
1970
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2. Mechanisms of population regulation
Environmental Factors
Abiotic
Habitats Light Temperature Precipitation Nutrients
Biotic
Intraspecific competition Interspecific
competition Grazing/predation Parasitism/disease
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Population regulation density-regulation
Mortality
Density-dependent
Density-independent
Rate of Birth or Death
Survival
Density-dependent
Population Density
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Population regulation Survival Strategy
Type I-Mammals
Survival Rate
Type II - Birds
Type III - Fish
Age
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Population Regulation prey-predator relationships
Prey
Predator
Abundance
Time
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Mechanisms Allowing Species Diversity Resource
Sharing and Niche Partitioning
1
3
2
Species
Relative Growth Rate
Resource State
Temporal or/and Spatial Variation
e.g. Habitats, Precipitation Light, Temperature,
Nutrients
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Mechanisms Allowing Species Diversity Predator
control
Predators
Relative Abundance
1
3
2
Species
Resource State
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Mechanisms of Population Regulation A Hierarchy
Approach
Land use change Climate change Succession Disturba
nce
Landscape Level
Birth rates Death rates Immigration Emigration Sex
ratio Age structure
Population Level
Growth rates Feeding rates Habitat
selection Predator Avoidance
Individual Level
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3. Habitat-specific demography
Sources and Sinks Metapopulation Concepts
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Equilibrium Theory of Island Biogeography Species
richness is the balance between colonization and
extinction rates
Colonization
Extinction
Near N
Small S
Rate of Colonization or Extinction
Large L
Far F
S-FS
S-FL
S-NL
S-NS
Low
High
Species Richness
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The key conservation legacies of the dynamic
theory of island biogeography were
1) Arriving at two most robust empirical
generalizations of biology and ecology
(1) Extinction rates decline with population
size (2) Immigration and recolonization rates
decline with increasing isolation
2) Species-area relationship 3) The metaphor of a
refuge as an island 4) The interest in the
fragility of the biota of individual refuges and
causes of this fragility 5) The rules of refuge
design
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Metapopulation Sources and Sinks
Sources good habitats where local reproductive
success is greater than local mortality and
individuals disperse outside their natural patch
to find a place to settle and breed. As little
as 10 of a metapopulation in source habitats may
be responsible for maintaining the 90 of the
population found in the sinks
Sinks poor habitats where local reproductive
success is less than local mortality and the
subpopulations rely on immigrations to avoid
extinction
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Implications of Sink and Source Concept for
conservation
1. Critical habitats should be defined by
habitat-specific reproductive success and
survivorship not population density --
important (Until recently, critical habitats
were defined as the places where a species was
most common). e.g. Peregrine Falcon two
subpopulations (northern California and southern
California) northern subpopulation acts as a
source for southern population.
2. Reserve design identify sources and
sinks Management strategy for Peregrine Falcon
focused on southern population (sink)
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Metapopulation
A population of a species that consists of
several subpopulations linked together by
immigration and emigration.
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Metapopulation, linked by local subpopulations

1. Patch
2. Size
3. Spatial structure
4. Linkage

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Metapopulation
Note Fragmented populations that is not linked
are not considered to be a metapopulation.
Rescue Effect local extinction of a
subpopulation can be prevented by occasional
immigrants that arrive from neighboring patches
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A fundamental assumption of the original
metapopulation concept
1) Space is discrete 2) It is useful and
possible to distinguish between habitat patches
that are suitable for the focal species and the
rest of the environment, often called matrix
Three critical elements
1) Density dependence in local population
dynamics 2) Spatial asynchrony in local
population dynamics (independent of other
subpoulations) 3) Limited dispersal linking the
local populations (migration has no real effect
on local dynamics in the existing populations)
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Sources and Sinks in a Metapopulation
Sink
Source
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Population Viability depends on
1. Demographic uncertainty (stochasticity) 2.
Environmental uncertainty (stochasticity) 3.
Natural catastrophes 4. Genetic uncertainty
(stochasticity)
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Population Viability Analysis (PVA)
PVA is the study of how these four factors
interact to determine extinction probability of a
population to estimate MVP. The MVP is the
product
MVP - Minimum Viable Population-imply some
thresholds for the of individuals that will
insure (at some acceptable level of risk) that a
population will persist in a viable state for a
given interval of time
Population persistence analysis
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Population Viability depends on

• 1. Demographic uncertainty (stochasticity)
• BIDE age structure sex ratio
• Metapopulation structure
• Fragmentation
• the immediate precursor for extinction
• independent of individuals

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Population persistence in years
Immigration rate (individuals/year)
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Extinction
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Population Viability depends on

• 2. Environmental uncertainty (stochasticity)
• A decrease in habitat quantity
• Habitat disturbance or deterioration in quality
• Realized via demographic stochasticity

A species also depends on habitats
Types --- where a species is (distribution) Qualit
y (suitability) --- population features density
(abundance), fecundity, body size Quantity
(areas) --- survival of a species (big
mammals) Pattern (arrangement) --- habitat
distribution for a metapopulation
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Population Viability depends on

• 3. Natural catastrophes
• Sudden change in environments
• Infrequent

In fact, they are large environmental
changes Fires Storms Hurricanes Earthquakes V
olcanoes
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4. Genetic uncertainty (Stochasticity)

• Mutation an alteration of an allele (or alleles)
  into a new allele (new alleles) due to changes in
  molecules, gene sequences or chromosomes
• Bottle neck a sudden reduction in a population
  size causes a genetic drift
• Genetic drift random changes in allele frequency
  due to chance alone, often occurring in a small
  population (so-called sampling error)
• Founder effect a genetic drift occurs when a few
  individuals separate from a large population and
  establish a new one
• Gene flow the change in allele frequencies due
  to immigration or emigration

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PVA Model
Biology of Individuals
Environmental Factors
Population Dynamics (demography)
Population Survival or Extinction
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PVA Model
Environmental disturbance
Biology of Individuals
Environmental Factors
--Growth --Population (P) --Distribution
Population Dynamics (demography)
Genetic effective P size
Demographic uncertainty
Extinction (Deterministic)
Extinction
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Deterministic extinction
extinction resulted from some inexorable change
or force from which there is no hope of escape.
E.g. -- Deforestation -- Glaciations -- Removal a
food source from animals
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PVA Model
Major loss of habitat
Biology of Individuals
Environmental Factors
Population Dynamics (demography)
Extinction (Deterministic)
Fragmentation
-- Population size -- Distribution
Extinction
Demographic randomness
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The case study of a bird the Florida Scrub Jay
1. Metapopulation types 2. Biology of the bird 3.
Spatial distribution of the bird 4.
Metapopulation structure
Dispersal distance Patch occupancy Population
viability analysis Characterization of
metapopulation
5. Conservation rules
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Biology of the Bird, the Florida Scrub Jay

• Floridas only endemic bird species
• Habitat specialist-scrub community on sandy
  infertile soils
• Strong preference for low, open habitats with
  numerous bare openings and few or no pine trees,
  which are caused by frequent fires
• Food acorns in winter
• Territorial defenders 10 ha per family
• Juveniles dispersal after one year
• The bird was listed as threatened species in 1987
  by the U.S. Fish and Wildlife Service (USFWS)

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Distribution of Florida scrub jay groups in 1993.
Note the discontinuous distribution and
variability in patterns of aggregation
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A subpopulation buffer is the distance where
occupancy rates remain high
Accumulative
97
85
Frequency
3.5 km
6.7 km
Dispersal Distance (km)
From natal to breeding territories 1970-1993
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The metapopulation buffer is the smallest
interpatch distance where occupancy rates reach
their minimum
Proportion of occupied patches
Interpatch Distance (km)
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Occupancy Proportions
Distance between patches (km)
Pairs
1 1.9 1.5 4 13
1-2 1-3 1-4 1-7 1-8
2/5
7
8
1
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Statewide jay distribution with dispersal
buffers. Shaded areas depict subpopulations
within easy dispersal distance (3.5 km) of one
another (191 separate subpopulations. Thick
outer lines delineate demographically independent
(42) metapopulations separated from each other by
at least 12 km
A metapopulation
12 km
3.5 km
A subpopulation
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Total 191 subpopulations
Frequency
Only Six subpopulations gt 100 birds
Subpopulation Size ( of birds)
Numbers above the bars indicate the number of jay
pairs
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Nonequilibrium metapopulations
Total 42 metapopulations
Frequency
Metapopulation Size
Numbers above the bars indicate the number of jay
pairs.
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Metapopulation Types
A dispersal buffer-an isoline of equal dispersal
probability
A subpopulation
A. Patchy
B. Classical
C. Nonequilibrium
D. Mainland-Island
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Nonequilibrium metapopulation
Functional subpopulation based on frequency of
dispersal beyond them
Separate metapopulations based on poorly
likelihood of dispersal among them
A set of small patches in which each has a high
probability of extinction and among which little
or no migration occurs. Local extinction are
not offset by recolonization, resulting in
overall decline toward regional extinction.
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Classical metapopulation
A set of small patches that are individually
prone to extinction but large enough and close
enough other patches that recolonization balances
extinction.
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Patchy metapopulation
Patches so close together that migration among
them is frequent hence the patches function over
the long run as a continuous demographic unit.
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Mainland-island metapopulation
A mixture of large and small patches close enough
to allow frequent dispersal from an
extinction-resistant mainland to the
extinction-prone islands
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Highly connected
Patchy
Mainland- Mainland
Mainland- Island
Patch isolation
Classical
High isolated
Nonequilibrium
Disjunct
All small
All large
Patch Size
Fig. 9.3.
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Mn-Mainland Md-midlands I-islands
Total of 4 island subpopulations with 2 pairs in
1 subpopulation
Total of 8 island populations with 1
subpopulations of one pair
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Examples of Nonequilibrium metapopulations
Fig. 9.10 North Gulf Coast of Florida each of
the 6 metapopulations contains fewer than 10
pairs of jays, except for the centrally located
system that contains a single, midland-sized
subpopulation
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Fig 9.11. Examples of a classical
metapopulation from 3 counties in central
Florida. Note the occurrence of jays in small
islands of intermediate distance from one another.
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Fig 9.12. Portion of the largest
mainland-midland-island metapopulation in
interior Florida.. The large central
subpopulation (enclosed by the thin black line)
contains nearly 800 pairs of jays. Small
subpopulations to the south and east are within
known dispersal distance of the large, central
mainland. A small metapopulation to the west (in
DeSoto County) contains a single subpopulation of
21 territories.
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Conservation Rules for the Florida scrub jay

• Preserve the cores
• Preserve all potentially viable metapopulations
• Preserve or enhance existing persistence
  probabilities
• Prohibit the splitting of a metapopulation
• Maintain connectivity within a metapopulation

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A comparison between island biogeography and
metapopulation

• Equilibrium Species richness vs Population
• Community approach vs population approach
• Community conservation (species richness-area
  relationship) vs focal species conservation
• Island theory ignore the changes in the presence
  and absences of individual species
• Among-patch movement

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Shift to Metapopulation paradigm in conservation
Metapopulation concept and approach is taking
over the equilibrium theory of island
biogeography in conservation biology

• Shift in the conception of nature as an
  equilibrium world to non-equilibrium one
• Population genetics genetic drift and
  inbreeding in a small population, becomes
  important because conservation question like
  what is minimum viable population? needs to be
  addressed.
• Species protection the role of demographic and
  environmental stochasticity
• Metapopulation concept incorporate spatial
  structure into population dynamics most
  significant, linked to habitat fragmentation
• Metapopulation models rescued small sites from
  their devaluation by island biogeography theory.

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Landscape Approach
Landscape

• A mosaic of habitat patches across which
  organisms move, settle, reproduce and eventually
  die.
• Heterogeneous within a landscape
• Patchy distribution of individuals - patches

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Landscape Approach
Modeling - spatially explicit models
Incorporate

• heterogeneous habitats
• patchy distribution of organisms

Depict

• The landscape structure
• The population demography

Project
the outcome when a disturbance to habitats
occurs, thus provide a management tool
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Spatially explicit model
A metapopulation model incorporate the actual
locations of organisms and suitable patches of
habitat, and explicitly consider the movement of
organisms among such patches.
Case of the Northern spotted owl
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Case of Northern Spotted Owl

• Habitat mature, old-growth coniferous forests
• Old, dense, large-trunk forest stands foraging,
  cover, nesting, breeding, fledging of young
• Life history juvenile dispersal from their natal
  areas, in search for both a suitable site and a
  mate
• Timber harvest, fire, clearing for agriculture
  and urban development reduce the habitat to 10
  of original
• Sparked the struggle between stakeholders
• Very intense, prolonged battle
• A petition for federal intervention under
  Endangered Species Act, -- given threatened
  status in 1990

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Landscape simulation
suitable habitat, randomly scattered
Fig. 8 The results are based on 30 simulations.
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Landscape simulation
Suitable habitats, 3 small blocks
Fig. 9. The results are based on 30 simulations.

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Landscape simulation
Suitable habitats, a large block
Fig. 10 The results are based on 30 simulations.

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Landscape simulation
Suitable habitat, 1 large irregular block
Fig. 11. The results are based on 30
simulations.
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Landscape simulation
Suitable habitats, irregular blocks like riparian
corridors
Fig. 12. The results are based on 30
simulations.
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Landscape simulation
Suitable habitats, clusters with marginal habitat
Standard deviations
Fig. 13 The results are based on 30 simulations.

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Endangered Species -- in danger of extinction
throughout all or a significant portion of its
range
Threatened species -- likely to become an
endangered species within the foreseeable future
throughout all or a significant portion of its
range.
Critical Species -- facing a very high
probability of extinction and require special
conservation measures.
200
Safe
150
Vulnerable
Endangered
Years
100
50
50
Critical
10
20
0.2
0.4
0.6
0.8
1.0
Probability of Extinction