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Habitat Fragmentation

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Title: Habitat Fragmentation


1
Habitat Fragmentation
  • ???(Ayo)
  • ???? ??????? ??
  • Japalura_at_hotmail.com

2
Introduction
  • Habitat fragmentation has two components
  • A reduction in the area covered by a habitat type
  • A change in habitat configuration
  • Essay 7.1 habitat shredding (???)

3
Contents
  • Fragmentation and heterogeneity
  • The fragmentation process
  • Biological consequences of fragmentation
  • Species vulnerable to fragmentation
  • Fragmentation versus habitat loss, and regional
    differences
  • The problem of climate change
  • Conclusion and recommendations

4
Supplements
  • Essay 7.1 habitat shredding
  • Essay 7.2 mosaics and patch dynamics
  • Box 7.1 Quantifying landscape pattern and
    fragmentation
  • Box 7.2 Species vulnerable to fragmentation
  • Case Study 7.1 Subdividing the west
  • Case Study 7.2 The fragmentation of aquatic
    ecosystems and the alteration of hydrologic
    connectivity neglected dimensions of
    conservation ecology
  • Case Study 7.3 Dissecting nature the islands of
    Lago Guri

5
Nature is patchy vs. shreded
  • Metapopulation models, landscape mosaic
    metaphors, and other nature is patchy concepts
    do not fit the shred configuration well.
  • Shredded landscapes may demand that ecologists
    develop new or modified models of population
    dynamics, demography, dispersal, and genetics, or
    that they apply the principles of landscape
    ecology.
  • Most importantly, the conservation consequences
    of shredded habitats may differ significantly
    from those of fragmented habitats.

Essay 7.1 habitat shredding
6
  • Shredded habitats invite empirical study and
    modeling in their own right, as ecologically
    interesting and significant landscape features
    along agricultural frontiers in the Neotropics at
    least.
  • They should arouse conservation concern, as
    possible refuges for native species, as corridors
    for, or barriers to exotics, and as potential
    reservoirs of native species for future
    restoration of their surroundings.

7
Patchiness is good?
  • If patchiness is good then why is fragmentation
    caused by humans perceived as bad?

8
Naturally patchy vs. fragmented landscapes
  1. Fragmentation has resulted in a reduction of the
    extent and connectivity of habitats, and species
    may or adjust to this change in habitat
    availability and configuration.
  2. A naturally patchy landscape has rich internal
    patch structure, whereas a fragmented landscape
    typically has simplified patches and matrix, such
    as parking lots, corn fields, clear-cuts, and
    tree farms.

9
  1. A natural landscape often has less contrast
    between adjacent patches than does a fragmented
    landscape, and therefore potentially less-intense
    edge effects.
  2. Certain features of fragmented landscapes, such
    as roads and various human activities, pose
    specific threats to population viability.

10
??????,????????????,?????
  • 1. Habitat diversity
  • 2. Population dynamics.
  • Priority effects
  • Multiple stable equilibria
  • Edge effects
  • Disturbance
  • Species pool and dispersal ability.
  • Colonization
  • Evolutionary effects.
  • Extinctions.
  • 3. Historical effects.

11
Fig. 13. ???????(???Case Code, 1987)
12
The fragmentation process
  • In terrestrial ecosystems, fragmentation
    typically begins with gap formation.
  • As the gaps get bigger or more numerous, they
    eventually become the matrix.
  • Fig. 7.4 (p.220)

13
Biological consequences of fragmentation
  • Initial exclusion
  • Crowding effect
  • Insularization and area effects
  • Isolation
  • Edge effects
  • Matrix effects
  • The special problem of roads
  • Species invasions

14
Fig. 7.13 populations of the forest-dwelling
carabid beetle Abax alter were almost completely
divided by a road and even by parking loops.
Lines represent movements of marked beetles
between capture and recapture points.
15
Species invasions
  • Roads may serve as conduits for the invasion of
    some species.
  • Roads favor species with good dispersal abilities
    in disturbed habitats at the expense of species
    with limited mobility.

16
Effects on ecological processes
  • Top-down regulation (Cascading effects)
  • Microclimate changes
  • Allee effect
  • Mutualisms
  • Low predictable sequence

17
Species not vulnerable to fragmentation
  • A species might survive or even thrive in the
    matrix of human land use.
  • These species are typically considered weedy
    and of little conservation concern.
  • a species might survive by maintaining viable
    populations within individual habitat fragments.
  • These species are with small home ranges.
  • Is to be highly mobile

18
Box 7.2Species vulnerable to fragmentation
  • Wide-ranging species
  • Nonvagile species (with poor dispersal abilities)
  • Species with specialized requirements
  • Large-patch or interior species
  • Species with low fecundity or recruitment
  • Species vulnerable to human exploitation or
    persecution

19
The problem of climate change
  • Fragmentation is a threat to biodiversity even in
    a relatively stable world.
  • If we add the phenomenon of rapid climate change,
    then we have perhaps the most ominous of all
    potential threats to biodiversity.

20
Conclusions and recommendations
  1. Conduct a landscape or seascape analysis
    (???,???? connections)
  2. Evaluate the landscape or seascape of interest
    within a larger context. What is the
    significance of this landscape to conservation
    goals at regional, national, and global scales?
  3. Avoid any further fragmentation or isolation of
    natural areas. (????)
  4. Minimize edge effects around remnant natural
    areas (establishing buffer zones)

21
  1. While conserving large, unfragmented patches of
    habitat, dont write off the small fragments.
    Such areas may be the last refuges for many
    species in highly fragmented regions and can
    maintain populations of many species for
    decades.
  2. Do not write off the landscape matrix as non
    habitat. There will rarely be enough area in
    reserves to conserve all of a regions
    biodiversity.
  3. Identify traditional wildlife migration routes
    and protect them.
  4. Maintain native vegetation along streams,
    fencerows, roadsides, powerline rights-of-way,
    and other remnant corridors in strips as wide as
    possible.

22
  1. Minimize the area and continuity of artificially
    disturbed habitats dominated by weedy or
    non-native species, such as roadsides, in order
    to reduce the potential for biological invasions
    of natural areas.
  2. Small fragments often suffer from disruption of
    natural processes, such as fire regimes. (Active
    management will be needed)
  3. Avoid dam construction, water diversions, and
    other activities that disrupt aquatic or
    hydrologic connectivity, and reverse these
    disruptions where possible.

23
Supplements
  • Case Study 7.1 Subdividing the west
  • Case Study 7.2 The fragmentation of aquatic
    ecosystems and the alteration of hydrologic
    connectivity neglected dimensions of
    conservation ecology
  • Case Study 7.3 Dissecting nature the islands of
    Lago Guri

24
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http//mail.nutn.edu.tw/hycheng/
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