Habitat Fragmentation

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Chapter 7

• Habitat Fragmentation

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What is a fragment?
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Habitat Fragmentation

• Disruption of large, continuous blocks of habitat
  into less continuous habitat
• Two components
• Reduction in area
• Change in habitat configuration
• Results in small, isolated natural areas among
  human settlements/activities

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Figure 7.1 in book adapted from Curtis 1956.
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Heterogeneity

• Most landscapes are made up of discreet patches,
  depending on scale
• Natural patchiness, or mosaics
• Differences due to
• Vegetation
• Soil type
• Elevation
• Microclimate effects of the above

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Metapopulations

• Systems of local population linked by occasional
  dispersal
• Requires patches are somehow accessible
• Persistence can not occur if patches are not
  connected
• Corridors, stepping stones, or other habitat for
  dispersal

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Is fragmentation good?

• What is the difference between natural patchiness
  andhuman-induced fragmentation?

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Natural vs. Human Fragments

• Still a popular area of investigation for
  ecologists and conservation biologists
• Can land management mimic natural patchiness?
• Some generalizations possible

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Hypotheses

• Fragmentation results in reduction of the extent
  and connectivity of habitats.

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Hypotheses

• Rich vs. simple patch structure

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Hypotheses

• Natural patchiness has less contrast and
  less-intense edge effects than fragments.

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Hypotheses

• Aspects of human-induced fragmentation pose
  additional threats to populations.

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Natural vs. Human Fragments

• Human-induced fragmentation creates different
  landscape and patchiness
• The degree of difference from natural landscape
  affects the degree of threat

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Process of Fragmentation

• Graduate process whereby the fragments become the
  matrix
• Matrix the most common habitat type

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Process of Fragmentation

• Loss of biological integrity is unknown
• Many factors contribute to effects of
  fragmentation
• Site fidelity
• Degree of mobility
• Delayed spatio-temporal effects

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Biological Consequences

• Initial exclusion
• Crowding effect
• Insularization and area effects
• Isolation
• Edge effects

• Matrix effects
• Roads
• Species invasions
• Ecological process

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Initial exclusion

• Elimination of species that only occurred in the
  portion of landscape destroyed
• Esp. important for endemic species, or narrowly
  distributed species
• Movement to another area of suitable habitat is
  one way to avoid this

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Crowding Effect

• Increase of individuals in an area of suitable
  habitat AFTER other portions have been destroyed
• Displacement results in initial population
  increase
• Not necessarily healthy population incr.
• Population crash quickly follows

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Crowding Effect

• Demonstrated in Brazil (Bierrgaard and Lovejoy
  1989)
• Natural patches fragments of varying sizes
  surveyed for birds
• SLOSS single large or several small
• Many factors affecting the answer to this
  question, some species/area dependent

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Bierrgaard and Lovejoy 1989
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Insularization and area effects

• Formation of island habitats
• Number of species declines as area available
  declines
• Protected areas may not be large enough

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Insularization and area effects

• Area sensitive species
• Species who seem to require more area than their
  home range/territory size would suggest
• Extinction of species increases as area decreases
• Particularly as the surrounding matrix changes,
  or becomes less suitable

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Isolation

• Occurs when habitat patch becomes increasingly
  surrounded by unsuitable habitat
• Vast expanses of unsuitable habitat form
  barriers to movement
• Results in inbreeding depression
• Reduced fitness because of breeding with related
  individuals

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Edge effects

• The boundary of a fragment is not a line, but a
  zone of influence
• Edge sealing in warmer climates
• Edge poses an ecological trap for some species

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Edge effects

• Edge of the habitat is of poorer quality than the
  interior (core) of the fragment

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Matrix effects

• Matrix most common habitat type
• Structural contrast between fragments and
  surrounding matrix
• Similar matrix effects
• May provide marginal habitat
• Facilitates movement among fragments

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Matrix effects

• Movement among fragments decreases as
  matrix-fragment structure differs
• Strong implications for intensity of edge effects

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Roads

• Often ignored source of fragmentation
• Considerations for conservation
• Mortality from road construction and collision
• Alteration of physical and chemical environments
• Spread of invasive species
• Increased potential for human interaction

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Roads

• Barriers to movements of many species

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Roads

• Hazards pose disproportionate threat for sex
  classes of some species
• Roads offer means of dispersal for invasive
  species

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Species invasions

• Use roads, power lines as corridors to new
  habitat fragments
• Results in increased species richness, although
  native species may suffer

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Effects on ecological processes

• Microclimate influences rates of nutrient
  cycling, decomposition
• Pollination rates vary with isolation or
  connectivity of fragments
• Ecosystems maintained by regular disturbance
  (fire) negatively impacted by fragmentation

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Biological Consequences

• Initial exclusion
• Crowding effect
• Insularization and area effects
• Isolation

• Edge effects
• Matrix effects
• Roads
• Species invasions
• Ecological process

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Species Vulnerable to Fragmentation

• Wide-ranging species
• Not simply sum of total fragment area
• Nonvagile species
• Low dispersal ability
• Specialized requirements
• Particular resource requirements
• Reliance on ephemeral habitats/resources

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Species Vulnerable to Fragmentation

• Large-patch or interior species
• Less likely to move through unsuitable habitat
• Low fecundity or recruitment
• Low reproductive capacity
• Value to humans
• Hunting/trapping species with high economic value
• Movement between fragments increases potential
  for harvest

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Climate Change and Fragmentation

• Both threats may pose a synergistic threat to
  biodiversity
• Threats to migratory species
• High elevation habitats may be lost

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How to counter effects of fragmentation?
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Connectivity

• The movement and genetic interchange of species
  such that viability is enhanced
• Ideally, conservation of largest tracts of
  habitat should be conserved
• Corridors, stepping stones, and other management
  tools to promote movement

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Yellowstone to Yukon

• Effort to maintain connectivity of mountainous
  region in westernNorth America
• http//maps.y2y.net/googlemap.htm

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Additional Recommendations

• Avoid further fragmentation/patch isolation
• Utilize buffer zones
• Consider matrix structure