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

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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
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• 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.

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Patchiness is good?

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

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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.

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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.

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??????,????????????,?????

• 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.

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Fig. 13. ???????(???Case Code, 1987)
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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)

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Biological consequences of fragmentation

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

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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.
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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.

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Effects on ecological processes

• Top-down regulation (Cascading effects)
• Microclimate changes
• Allee effect
• Mutualisms
• Low predictable sequence

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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

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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

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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.

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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)

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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.

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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.

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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

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