Transcript Habitat Fragmentation

Habitat Fragmentation
• Habitat fragmentation is the seperation of a landscape into various
landuses (e.g, development, agriculture, etc.), resulting in numerous
small, disjunct habitat patches left for use by wildlife.
• As the name implies, it describes the emergence of discontinuities
(fragmentation) in an organism's preferred environment (habitat)
• Fragmentation eliminates habitat for those species requiring large
unbroken blocks of habitat
• This disconnection of natural
habitat amplifies the negative
effects of decreasing total
habitat area
Causes of Fragmentation
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Urbanization
Agriculture
Transportation
Deforestation
Resource Extraction
Flood control and hydroelectric dams
Oil and gas pipelines
Edge Effects
• When an edge is created to any natural ecosystem, and the area outside
the boundary is a disturbed or unnatural system, the natural ecosystem
is seriously affected for some distance in from the edge.
• In the case of a forest where the adjacent land has been cut, creating an
openland/forest boundary, sunlight and wind penetrate to a much
greater extent, drying out the interior of the forest close to the edge and
encouraging rampant growth of opportunistic species at the edge.
• Air temperature, soil moisture, light intensity and levels of
photosynthetically active radiation (PAR) all change at edges.
Edge Effects
• The effect of having more edge habitat and less interior
space is that edge species increase and interior species
decrease
Other Impacts
• Fragmentation eliminates habitat for those species requiring
large unbroken blocks of habitat (e.g., bobcats and grizzly bears,
deer).
• Additionally, the small habitat patches resulting from
fragmentation often do not provide the food and cover resources
for many species that do attempt to use them
• This can result in an increased risk of death by predation, if the
animal has to venture beyond the cover of the patch to find new
food resources, or starvation.
• Leaving the safely on interior spaces forces many sepcies into
open spaces where the are more easily preyed apon
• Once habitat is fragmented there is an island effect whereby species
extirpated due to predation or disease are unlikely to be naturally
reintroduced to the area
Degree of Fragmentation
• Large patches are typically considered more important than
smaller ones because they tend to include more viable
populations of native plants and animals, including species
dependent on interior habitat
• However, small patches
can also be important
conservation targets
because they may contain
unique or rare habitat types
or species or may act
as stepping stones.
Small patches may
also provide sufficient
habitat for species that
don’t have large area
requirements.
Size Matters!!
• Larger patches have more interior habitat,
while smaller patches have less or no interior
habitat.
Size Matters!!
• Populations are typically more stable and
sustainable and less susceptible to local
extinction in large patches than small patches.
Size Matters!!
• A large patch often contains greater habitat and species
diversity than a small patch. More importantly, large
patches are more likely to maintain native species in
good quality habitat, whether or not greater diversity
naturally occurs or not.
Staying Connected
• Species movement among habitat patches can be facilitated
through the protection of discrete spatial features such as
stepping stones and linkages or through surrounding matrix
lands that allow movement among patches
• Proximity and location
of patches and the
specific behavior and
life histories of the
target species are also
factors in determining
species movement
among habitat
patches
Staying Connected
• Interconnectedness is an important feature of networks,
as it facilitates species movement among patches.
• Small interconnected patches provide cover, resting,
and foraging habitats for animals en route to larger
habitat patches.
• However, a network that
is designed for connectivity
but ignores other principles
may have too much linear
habitat and edge.
Time to “Shape” up
• Irregularly shaped parcels have more edge habitat and
edge species and less interior habitat and interior
species than round shaped parcels.
• Also, irregularly shaped patches have greater
interaction with the
surrounding habitat
matrix, increasing chances
for negative interactions
such as habitat degradation
from adjacent land use or
other disturbances.
Time to “Shape” up
• Linear shaped patches, including corridors and
riparian buffers, contains little or no interior
habitat, while blocks of habitat in a rounder
shape has more interior habitat.
© 2003 Defenders of
Wildlife. All rights reserved.
What is a “Buffer”
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A buffer is essentially a ring of protective habitat that surrounds an
natural area.
It provides a gradual transitional zone from one ecosystem to another
(ecotone) minimizing negative edge effects that are often associated with
habitat fragmentation
The creation of a buffer zone
will reduce animal contact
with unfriendly land use.
Buffer zones are used to protect
natural or restored areas from
pollutants such as nutrients,
pesticides and sediments, and
from physical impacts such
as encroachment.
The desired width of a buffer
zone is dependant upon
topography, adjacent land use,
and the home ranges of the
animals present.
Corridors
• A Corridor is a natural or artificial connection between two pieces
of fragmented habitat
• corridors facilitate everyday home range movements, seasonal and
breeding migrations, dispersal, and range shifts in response to
environmental and climatic changes
• Corridors connecting
fragments of isolated habitat
provide a safe passageway
allowing for immigration and
emigration of animals aiding
gene flow and decreasing the
chance of local extinction
events