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BISC530: Biology Conservation Kedong Yin. Introduction Habitat fragmentation Demographic Processes on heterogeneous landscapes: Metapopulation dynamics. Demographic Processes: Population Dynamics on Heterogeneous Landscape. What is population demography? Mechanisms of population regulation

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Bisc530 biology conservation kedong yin
BISC530: Biology ConservationKedong Yin

  • Introduction

  • Habitat fragmentation

  • Demographic Processes on heterogeneous landscapes: Metapopulation dynamics


Demographic Processes: Population Dynamics on Heterogeneous Landscape

What is population demography?

Mechanisms of population regulation

Habitat-specific demography

Population viability analysis

The landscape approach


1. What is population demography? Landscape

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

Immigration

Emigration

Death


6 Landscape

1945

1985

1940

Years



Hong Kong Sex Ratio Landscape

Age

35

0

Female

Male


District Landscape

81

86

91

81-86

86-91

81-91

Tuen Mun

Sha Tin


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


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 Factors

Mortality

Density-dependent

Density-independent

Rate of Birth or Death

Survival

Density-dependent

Population Density


Population regulation: Survival Strategy Factors

Type I-Mammals

Survival Rate

Type II - Birds

Type III - Fish

Age


Population Regulation: prey-predator relationships Factors

Prey

Predator

Abundance

Time


Mechanisms Allowing FactorsSpecies Diversity:

Resource Sharing and Niche Partitioning

Species

1

2

3

Relative Growth Rate

Resource State

Temporal or/and Spatial Variation

e.g. Habitats, Precipitation

Light, Temperature, Nutrients


Mechanisms Allowing Species Diversity: Factors

Predator control

Predators

Relative Abundance

Species

1

2

3

Resource State


Mechanisms of Population Regulation: Factors

A Hierarchy Approach

Land use change

Climate change

Succession

Disturbance

Landscape Level

Birth rates

Death rates

Immigration

Emigration

Sex ratio

Age structure

Population Level

Growth rates

Feeding rates

Habitat selection

Predator Avoidance

Individual Level


3. Habitat-specific demography Factors

Sources and Sinks:

Metapopulation Concepts


Equilibrium Theory of Island Biogeography: Factors

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 #


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 island biogeography were:

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: island biogeography were:

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: island biogeography were:

A population of a species that consists of several subpopulations linked together by immigration and emigration.


Metapopulation, linked by local subpopulations island biogeography were:

  • Patch

  • Size

  • Spatial structure

  • Linkage


Metapopulation: island biogeography were:

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)



Population Viability depends on: concept

1. Demographic uncertainty (stochasticity)

2. Environmental uncertainty (stochasticity)

3. Natural catastrophes

4. Genetic uncertainty (stochasticity)


Population Viability Analysis (PVA) concept

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: concept

  • 1. Demographic uncertainty (stochasticity)

  • BIDE + age structure + sex ratio

  • Metapopulation structure

  • Fragmentation

    • the immediate precursor for extinction

    • independent of individuals


Population persistence in years concept

Immigration rate (individuals/year)


% Extinction concept


Population Viability depends on: concept

  • 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: concept

  • 3. Natural catastrophes

    • Sudden change in environments

    • Infrequent

In fact, they are large environmental changes

Fires

Storms

Hurricanes

Earthquakes

Volcanoes


4. Genetic uncertainty (Stochasticity) concept

  • 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 concept

Biology of Individuals

Environmental Factors

Population Dynamics (demography)

Population Survival or Extinction


PVA Model concept

Environmental disturbance

Biology of Individuals

Environmental Factors

--Growth

--Population (P)

--Distribution

Population Dynamics (demography)

Genetic effective P size

Demographic uncertainty

Extinction

(Deterministic)

Extinction


Deterministic extinction: concept

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


PVA Model concept

Major loss of habitat

Biology of Individuals

Environmental Factors

Population Dynamics (demography)

Extinction

(Deterministic)

Fragmentation

-- Population size

-- Distribution

Extinction

Demographic randomness


The case study of a bird: the Florida Scrub Jay concept

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 concept

  • 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

97%

85%

Frequency

3.5 km

6.7 km

Dispersal Distance (km)

From natal to breeding territories 1970-1993


The metapopulation buffer is the smallest interpatch distance where occupancy rates reach their minimum

Proportion of occupied patches

Interpatch Distance (km)


Pairs distance where occupancy rates reach their minimum

Distance between patches (km)

Occupancy Proportions

1

1.9

1.5

4

13

1-2

1-3

1-4

1-7

1-8

2/5

7

8

1


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


Total 191 subpopulations areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

Frequency

Only Six subpopulations > 100 birds

Subpopulation Size (# of birds)

Numbers above the bars indicate the number of jay pairs


Nonequilibrium metapopulations areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

Total 42 metapopulations

Frequency

Metapopulation Size

Numbers above the bars indicate the number of jay pairs.


Metapopulation Types areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

A dispersal buffer-an isoline of equal dispersal probability

A subpopulation

A. Patchy

B. Classical

C. Nonequilibrium

D. Mainland-Island


Nonequilibrium metapopulation areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

A mixture of large and small patches close enough to allow frequent dispersal from an extinction-resistant mainland to the extinction-prone islands


Highly areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

connected

Patchy

Mainland-

Mainland

Patch

isolation

Mainland-

Island

Classical

High

isolated

Nonequilibrium

Disjunct

All small

All large

Patch Size

Fig. 9.3.


Mn-Mainland areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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. areas depict subpopulations within easy dispersal distance (3.5 km) of one another (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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (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.


Conservation Rules for the Florida scrub jay areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

  • 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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

  • 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: areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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.


Landscape Approach: areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

  • 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 areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

suitable habitat, randomly scattered

Fig. 8 The results are based on 30 simulations.


Landscape simulation areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

Suitable habitats, 3 small blocks

Fig. 9. The results are based on 30 simulations.


Landscape simulation areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

Suitable habitats, a large block

Fig. 10 The results are based on 30 simulations.


Landscape simulation areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

Suitable habitat, 1 large irregular block

Fig. 11. The results are based on 30 simulations.


Landscape simulation areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

Suitable habitats, irregular blocks like riparian corridors

Fig. 12. The results are based on 30 simulations.


Landscape simulation areas depict subpopulations within easy dispersal distance (3.5 km) of one another (

Suitable habitats, clusters with marginal habitat

Standard deviations

Fig. 13 The results are based on 30 simulations.


Endangered Species areas depict subpopulations within easy dispersal distance (3.5 km) of one another ( -- 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

20

10

Critical

0.2

0.4

0.6

0.8

1.0

Probability of Extinction


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