Habitat fragmentation involves reducing the area of habitats and dividing remaining areas into smaller, isolated patches. It results in reduced habitat extent and connectivity. Fragmentation begins with gap formation and increases until the gaps become the dominant landscape feature. This severs original habitat connectivity. Fragmented landscapes have simplified patches and matrix with less contrast between patches, intensifying edge effects. Certain threats like roads specifically endanger population viability. Species vulnerable to fragmentation include those with narrow ranges, poor dispersal ability, specialized requirements, or low fecundity, as they struggle to adjust or are isolated in fragments.

1. S. R. Maharjan
Asst. Professor
Tribhuvan University

2.  Habitat fragmentation is the conversion of
landscape to small fraction of its former area
 Habitat fragmentation has two components:
◦ A reduction in the area covered by a habitat type
◦ A change in habitat, with remaining habitat divided into
smaller and isolated patches
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3.  Fragmentation and heterogeneity
 The fragmentation process
 Biological consequences of fragmentation
 Species vulnerable to fragmentation
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4. 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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5. 3. A natural landscape often has less contrast
between adjacent patches than does a
fragmented landscape, and therefore potentially
less-intense edge effects.
4. Certain features of fragmented landscapes, such
as roads and various human activities, pose
specific threats to population viability.
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6.  In terrestrial ecosystems, fragmentation typically
begins with gap formation.
 As the gaps get bigger or more numerous, they
eventually become the matrix.The connectivity of
original vegetation is broken.
 At this point, in the fragmentation process, it
ceases to support some species
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7.  Initial exclusion
 Crowding effect
 Insularization and area effects
 Isolation
 Edge effects
 Matrix effects
 The special problem of roads
◦ Species invasions
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8.  One of the rapid effect of fragmentation is
elimination of species that are endemics with
narrow distribution.
◦ Eg. 90 species of plants were lost when small patch of
forest destroyed by logging
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9.  When habitat is isolated by fragmentation,
population density of animals increase in
fragments.
 Population of large habitats will be displaced in
small fragments, known as crowding effect.
◦ Eg In Amazonian forest of Brazil, capture rate of
understorey birds in a 10 ha fragment increased more
than double after its isolation
◦ Density of ovenbirds increased in forest fragments due to
logging.
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10.  The number of species decrease with
decline of insular(like an island) habitat
◦ A small island or nature reserve may be smaller
than the territory or home range of organism
◦ A cougar is unlikely to ramain in 100 ha park
which requires average of 400 km2.
◦ Grizzly bears reuire 900 km2
◦ in N america, parks smaller than 9500 km2 didn’t
sustained wolves population
◦ Animals are vulnerable to mortality while attempts
to travel through fragments
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12.  Species with specific habitat requirements depend
on many habitat patches in close proximity
 Many animals require a mix of different habitat
with distinct resources- roosting sites, breeding
sites, food patches etc.
 Human created barriers- roads, urban areas,
agricultural lands, clearcuts inhibit movement and
affect population viability
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14.  Reduction in genetic diversity
 Inbreeding depression (reduced biological fitness
due to inbreeding) increase extinction risks
 Human created barriers such as dams also
fragment freshwater habitats, block migration and
recolonization of freshwater fishes
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15.  Best documented impacts
 Outer boundary influenced by light and wind
 Shade intolerate species dominate due to edge
effect.
 Accelerated growth of trees and shrubs
 Animals attracted to edge, ecological trap
 Birds- Brood parasitism/ nest predation
 Extinction od interior birds/ no core areas
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Cowbird parasitism

17.  Matrix- landscape surrounding habitat fragments
 Alteration of matriz increase isolation
 When contrast of matrix increase, edge effect also
increase
 Diversity of birds is lower in patches surrounded
by urban areas
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18.  Habitat fragmentation supplemented by road
construction
 Effects of roads documented-
◦ Mortality from road construction
◦ Mortality from collision with vehicles
◦ Modification of animal behaviour
◦ Alteration of physical environment
◦ Alteration of chemical environment
◦ Spread of invasive species
◦ Increase of edge effects
◦ Barriers for animals
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19.  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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20.  Top-down regulation (Cascading effects)
 Microclimate changes decrease invertibrate
communities
 Allee effect(below some threshold population size,
no pollinators visit)
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21.  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
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