bisc530: biology conservation kedong yin introduction habitat fragmentation demographic processes...

BISC530: Biology ConservationKedong Yin

Introduction Habitat fragmentation Demographic Processes on

heterogeneous landscapes: Metapopulation dynamics

Key references: Meffe and Carroll and et al. 1997. The Principles of Conservation Biology. Sinauer Assoc. Inc.

McCullough, DR. 1996. Metapopulation and Wildlife Conservation Chapter 9

http://teaching.ust.hk/~bisc530/

Biological Conservation

Genetic material

Gene pools

Species

Populations

Communities

Habitats

Ecosystems

Biosphere

Focal levels of Conservation

Introduction

1. The diversity of organisms is good

2. The untimely extinction of populations and species is bad

3. Ecological complexicity is good

4. Evolution is good

5. Biological diversity has intrinsic values

Some postulates in conservation biology:

Biodiversity

Species diversity remain to be the most important one

Focusing on important species may provide short cuts to conservation

Keystone taxa: predominating ecological role in community they may help to characterize

Umbrella taxa: species providing “shelter” for many others

Flagship taxa: public appeal

Indicator taxa: environmental change

Guiding Principles for Conservation Biology

Principle 1: Evolution is the basic axiom that unites all of biology

(the evolutionary play)

Principle 2: The ecological world is dynamic and largely non-equilibrial

(the ecological theatre)

Principle 3: The Human presence must be included in conservation planning

(Humans are part of the play)

Habit Fragmentation:

1. Habitat fragmentation

2. Fragmentation and Heterogeneity

3. The Fragmentation Process

4. Insularization and Area effects

5. Biological Consequences of Fragmentation

Historical lessons on habitat loss:

Classified Greek period -- the barren landscape of deserts in the middle east (Turkey, Syria, Irag and Iran) used to be fragile woodlands

Humid tropics -- shifting practices with gaming, rotating practices in farming, not possible in crowded world today

Europe -- Great Britain, many forests destroyed by 12th century, public forests eliminated by the late 18th century, due to the demand for charcoal supply

1. Habitat fragmentation: Reduction of the total amount of a habit type,

or perhaps of all natural habitat in a landscape

Divide a continuous landscape into smaller, more isolated patches

Critical habitat -- a specific area within the species range with physical or biological features

either

(1) essential to conservation of the species

or

(2) which may require special management considerations or protection

Fig. 9.1 Changes in wooded area of Cadiz Township, Green Country, Wisconsin, during the period of European settlement.

Wooded area

1831 1882

1902 1950


Patches (heterogeneity) vs continuous (homogeneous), a matter of scales: zoom in or zoom out

A side view of the mountain

Different vegetations

High mortality patch

Medium mortality patch

Low mortality patch

Large disturbances like fires create a course grained pattern

Small disturbances – a fine-grained pattern

Different 7 phases of canopy gaps by death and fall of individual trees

10 km

1 km


Spatial scale (physical gradients, light, moisture, elevation) Temporal (seasonality) Disturbances (fires, storms) Microhabitats

Patches (heterogeneity) vs continuous (homogeneous), a matter of scales: zoom in or zoom out

So, if habitat heterogeneity is good for diversity, what is the difference between human-fragmented and natural patchy landscape?

Internal structure Edge effects Barriers Evolutionary

Biological integrity -- Ecological system Disruption of continuity in pattern or

processes

Spatial scale Temporal scale

3. The Fragmentation Process:

Gap formation

Fragmentation

A

B

C

Typical Habitat FragmentationA ranch subdivided into ranchettes

Building

1957 1983 1994

FragmentationPopulation Density

RoadsFences

Subsidized predatorsExotic Species

Nuisance problemsWildlife generalistsWildlife Specialists

Increase

Decreases in #

Effects when land is subdivided into ranchettes

Area-species relationship: difference between island and a patch of habitat, or

A phenomenon of statistic sampling The equilibrium theory of island biogeography

4. Insularization and Area effects:

S=cAZ or Log S = Log C + z Log AS=species richness, A= area, c- constant

S

A

Log

S

A

Log

S

Island

Quadrats

Probability of occurrence of birds vs forest areas

Equilibrium Theory of Island Biogeography:Species richness is the balance between colonization and extinction rates

Low High

FS NS FL NL

Colonization Extinction

Far: F

Large: L

Near: N Small: S

Species Richness #

Rat

e of

Col

oniz

atio

n o

r E

xtin

ctio

n

1) Speciation

2) Initial exclusion:

3) Barriers and Isolation

4) Crowding effects

5) Local and Regional Extinctions

6) Species vulnerable to fragmentation

7) Edge Effects

8) Changes in Species Composition

9) Effects on Ecological Processes

5. Biological Consequences of Fragmentation:

1) Speciation

Speciation: a process a new species is formed.

Speciation process is ultimately a genetic divergence between populations through time, reflecting local adaptation

How selection works: giraffe long neck

Selective pressure toward a longer-necked, taller animalSelective

pressure stops

Many generations

Short-necked animals starve and die. Gene for shorter neck does not enter gene pool

Gradual allopatric speciation

Bar

rier

A

A

AA

AA

AAA A A

AAAA A A

AA A

AAAA

A B B

BB B

AA AA

AB

BB

B

B

Founder model or Quantum Speciation

A

AA

AA

AAA A A

A

AA

AA

AAA A A

A

AA

AA

AAA A A

A

A AA

B

B BB

Gradual Allopatric Speciation: Arctic vs Gray fox

Subpopulations spread northward and southward and separate

Conditions differ giving different selective pressures causing evolution into different species

Adaptations to cold climate: heavy fur; short tail, ears, legs, and nose; light color

Adaptations to warm climate: thin fur; long tail, ears, legs, and nose; dark color

Arctic Fox Gray Fox

Exmaple of quantum speciation of finches

Darwin’s finches. The similarities among these birds attest to their common ancestor. Selective pressures adapting subpopulations to feed on different foods has caused their modification and speciation.

Warbler Cactus Ground

Sharp-Beaked Ground

Vegetarian

Large insectivorous

Small insectivorous

Woodpecker Sharp-Beaked Ground

Small Ground

Medium Ground

Large Ground

Geographic modes of speciation:

1) Gradual allopatric speciation

Reproductive isolation is a result of divergence. If divergence is relatively short, the two groups comes into second contact-hybrid-no advantage -stable . If long, hybrids -- natural selection works -- become distinguishable specie.

2) Founder model or quantum speciation

small gene pool

gene drift -- genetic drift--rapid and substantial genetic change

speciation -- rapid

Effects of fragmentation of habitats on the speciation

Two scenarios:1) quantum speciation occurs rapidly and results in

several species

2) local extinction -- more quickly than speciation

A

AA

AA

AAA A A

A A

AAA A

A

A C

DA

B A

A A

A

A

12

2) Initial Exclusion

One of the most rapid and obvious effects of fragmentation: elimination of the species by the initial exclusion

Home ranges are destroyed, endemic species are sometimes quite restricted in its distribution, many rare species are endemics with narrow distributions

Species with narrow distribution are vulnerable when their habitat is fragmented

Endemic species: species only exist in this country, not in other countries; or in this area not in other areas.

A

B

A constellation of separate habitat patches may be critical to the survival of individuals or populations. When a species requires several patches (green area) to survival, then species in site A would survive better.

A species require several patches to survive

A

B


A

B

Many animals require a suite of different habitats or resources to survive. A population in Site A in the proximity of different habitat B would survive better than in Site B.

A species require different habitats (A and B) to survive

A

B

Roads as barriers to the movement of small animals

N>100N>50N>20

Beetle density

Carabid beetles releasing experiment

Lines – movement of marked bettles between capture and recapture


A constellation of separate habitat patches – critical to the survival of a population

A mix of different habitats with different resources- important

Barrier: species specific

Roads as a major barrier to many species

Barrier effects are both relative and cumulative

Structural contrast between fragmented habitats and the matrix for the species is one measure of fragmentation, as the landscape around fragments is altered, the functional isolation of these fragments increases

Dams or other marine engineering projects

1) Speciation



Barriers are species specificRelative and cumulative

4) Crowding effects


4) Crowding Effects

Population densities may initially increase in the fragment when the fragment is isolated

This packing phenomenon – “crowding on the ark”

The initial increase is often followed by the population collapse

1) Speciation


Home ranges are destroyed, endemic species are sometimes quite restricted in its distribution



4) Crowding effects


Even common species can disappear from the fragments when the fragments are altered.


1) Speciation





4) Crowding effects




Species vulnerability Abundance Extent of ecological specialization Geographical range


Naturally rare species:

a) Species with limited or patchy geographic distributions (e.g. endemic species)

b) Species with low population densities (e.g. animals with a large home range)

Wide-ranging species: large carnivores needs a large area for food hunting or seasonal movement

Nonvagile species: species with poor dispersal abilities may not travel far from their birth place, e.g. many insects of old growth forests

Species with low fecundity: species with low reproductive capacity


Species with short life cycles: more vulnerable than longer-lived species

Species dependent on patchy or unpredictable resources or otherwise highly variable in population size

Grounded Nesters: nesting on or near the ground

Large-patch or interior species: species living in the interior of a habitat, thus vulnerable to fragmentation of their habitat

Species vulnerable to human exploitation or persecution

1) Speciation





4) Crowding effects



7) Edge Effects


7) Edge Effects

There is edge if a habitat island is different from the surrounding landscape

There is a gradient of environmental factors across the edge

Ecological trap: animals are attracted to edge habitat

The structural contrast to the surrounding landscape is an indicator of the strength of edge effects

The ratio of the edge length to the interior area is a measure of the edge effects

Loss of quail eggs

A comparison of breeding success of fragmentation sensitive birds (16 species) in two forest fragments with similar total areas, but vastly different core areas (forest interior).

A is entirely edge habitat (light);

B contains 20 ha of interior habitat.

No birds bred successfully

6 species / 16 species bred in core area

A

B

39 ha

47 ha

20 ha

1) Speciation





4) Crowding effects



7) Edge Effects



1) Speciation





4) Crowding effects



7) Edge Effects


9) Effects on Ecological Processes


Species Persistence in a fragmented landscape:

3 options

Survive well or thrive in a matrix of human land uses: weedy species

Maintain viable population within individual habitat fragments: species with a small home range

Highly mobile: some birds

Habit Fragmentation:

1. Habitat fragmentation2. Fragmentation and Heterogeneity3. The Fragmentation Process 4. Insularization and Area effects5. Biological Consequences of

Fragmentation

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