Transcript BISC530: Biology Conservation Kedong Yin

BISC530: Biology Conservation
Kedong Yin
 Introduction
 Habitat fragmentation
 Demographic Processes on
heterogeneous landscapes:
Metapopulation dynamics
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
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
Immigration
Structure
Death
Emigration
6
1945
1940
1985
Years
Hong Kong Age Structure in 1998
Age
Hong Kong Sex Ratio
35
0
Female
Male
District
Tuen Mun
Sha Tin
81
86
91
81-86 86-91 81-91
Seal Population changes on two islands occupied by US Coastal
Guard:
Juvenile survival is important in conserving seal populations
Tern Island
Coastal Guard in
Number of Seals
Coastal
Guard out
Green Island
1960
1970
1980
2. Mechanisms of population regulation:
Environmental Factors
Abiotic:
Habitats
Light
Temperature
Precipitation
Nutrients
Biotic:
Intraspecific competition
Interspecific competition
Grazing/predation
Parasitism/disease
Population regulation: density-regulation
Mortality
Density-dependent
Density-independent
Density-dependent
Population Density
Survival
Population regulation: Survival Strategy
Type I-Mammals
Type III - Fish
Age
Population Regulation: prey-predator relationships
Abundance
Prey
Predator
Time
Mechanisms Allowing Species Diversity:
Resource Sharing and Niche Partitioning
Species
1
2
Resource State
e.g. Habitats, Precipitation
Light, Temperature, Nutrients
3
Temporal
or/and
Spatial
Variation
Mechanisms Allowing Species Diversity:
Predator control
Predators
Species
1
2
Resource State
3
Mechanisms of Population Regulation:
A Hierarchy Approach
Landscape Level
Population Level
Individual Level
Birth rates
Death rates
Immigration
Emigration
Sex ratio
Age structure
Land use change
Climate change
Succession
Disturbance
Growth rates
Feeding rates
Habitat selection
Predator Avoidance
3. Habitat-specific demography
Sources and Sinks:
Metapopulation Concepts
Rate of Colonization or Extinction
Equilibrium Theory of Island Biogeography:
Species richness is the balance between colonization and
extinction rates
Colonization
Near: N
Extinction
Small: S
Large: L
Far:
F
S-FS S-NS S-FL S-NL
Low
High
Species Richness #
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
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
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)
Metapopulation:
A population of a species that consists of several
subpopulations linked together by
immigration and emigration.
Metapopulation, linked by local subpopulations
1. Patch
2. Size
3. Spatial structure
4. Linkage
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
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)
Sources and Sinks in a Metapopulation
Source
Sink
Population Viability depends on:
1. Demographic uncertainty (stochasticity)
2. Environmental uncertainty (stochasticity)
3. Natural catastrophes
4. Genetic uncertainty (stochasticity)
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
Population Viability depends on:
1. Demographic uncertainty (stochasticity)
BIDE + age structure + sex ratio
Metapopulation structure
Fragmentation
the immediate precursor for extinction
independent of individuals
Immigration rate (individuals/year)
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)
Quality (suitability) --- population features: density
(abundance), fecundity, body size
Quantity (areas) --- survival of a species (big mammals)
Pattern (arrangement) --- habitat distribution for a
metapopulation
Population Viability depends on:
3. Natural catastrophes
Sudden change in environments
Infrequent
In fact, they are large environmental changes
Fires
Storms
Hurricanes
Earthquakes
Volcanoes
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
PVA Model
Biology of
Individuals
Environmental
Factors
Population
Dynamics
(demography)
Population Survival or Extinction
Environmental
disturbance
PVA Model
Biology of
Individuals
Environmental
Factors
Population
Dynamics
(demography)
--Growth
--Population (P)
--Distribution
Genetic effective P size
Demographic uncertainty
Extinction
Extinction
(Deterministic)
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
Major loss of habitat
PVA Model
Biology of
Individuals
Environmental
Factors
Population
Dynamics
(demography)
Fragmentation
-- Population size
-- Distribution
Extinction
Demographic randomness
Extinction
(Deterministic)
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
Biology of the Bird, the Florida Scrub Jay
Florida’s 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)
Distribution of
Florida scrub jay
groups in 1993. Note
the discontinuous
distribution and
variability in patterns
of aggregation
A subpopulation buffer is the distance where occupancy rates
remain high;
Accumulative
Frequency
97%
85%
3.5 km
6.7 km
Dispersal Distance (km)
From natal to breeding territories 1970-1993
Proportion of occupied patches
The metapopulation buffer is the
smallest interpatch distance where
occupancy rates reach their minimum
Interpatch Distance (km)
Pairs
Distance between patches Occupancy Proportions
(km)
1-2
1
1-3
1.9
1-4
1.5
2/5
7
1-7
4
1-8
13
8
1
A metapopulation
12 km
3.5 km
A subpopulation
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
Total 191 subpopulations
Only Six
subpopulations >
100 birds
Subpopulation Size (# of birds)
Numbers above the bars indicate the number of jay pairs
Frequency
Nonequilibrium
metapopulations
Total 42 metapopulations
Metapopulation Size
Numbers above the bars indicate the number of jay pairs.
A dispersal buffer-an
isoline of equal
dispersal probability
Metapopulation Types
A subpopulation
A. Patchy
B. Classical
C. Nonequilibrium
D. Mainland-Island
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.
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.
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.
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
Highly
connected
Patchy
Patch
isolation
Classical
MainlandIsland
High
isolated
Nonequilibrium
All small
Fig. 9.3.
MainlandMainland
Disjunct
All large
Patch Size
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
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
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.
Fig 9.12. Portion of the largest
mainland-midlandisland 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.
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
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
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 nonequilibrium 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.
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
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
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
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
Landscape simulation
suitable habitat,
randomly scattered
Fig. 8 The results are based on 30 simulations.
Landscape simulation
Suitable habitats, 3
small blocks
Fig. 9. The results are based on 30 simulations.
Landscape simulation
Suitable habitats, a
large block
Fig. 10 The results are based on 30 simulations.
Landscape simulation
Fig. 11. The results are based on 30 simulations.
Suitable habitat, 1
large irregular
block
Landscape simulation
Fig. 12. The results are based on 30 simulations.
Suitable habitats,
irregular blocks
like riparian
corridors
Landscape simulation
Suitable habitats, clusters with
marginal habitat
Standard
deviations
Fig. 13 The results are based on 30 simulations.
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
150
100
50
50
20
10
0.2
0.4
Critical
0.6
0.8
Probability of Extinction
1.0