Habitat Fragmentation

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Habitat Fragmentation
Photo of a fragmented Valdivian forest in Chile
from www.tncfire.org
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Habitat Fragmentation
Habitat fragmentation is an anthropogenic
disturbance
Disturbance a discrete event that removes
biomass (and thereby can create heterogeneity
or patchiness)
Photo of a fragmented Valdivian forest in Chile
from www.tncfire.org
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Habitat Fragmentation
Habitat fragmentation is an anthropogenic
disturbance
with two components (1) A reduction in area of
the focal habitat type
(2) A change in habitat configuration remaining
patches are smaller and more isolated than in
the original configuration
Photo of a fragmented Valdivian forest in Chile
from www.tncfire.org
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Nature is Inherently Patchy
Space-time Mosaic (Watt 1947) Shifting Mosaic
(Bormann Likens 1979) Patch Dynamics Crazy
Quilt (H. S. Horn)
Natural disturbance regime
Green Eastern hemlock
Purple American beech
Red Red maple
Yellow Yellow birch
500 yr
1000 yr
Images from Deutschman et al. (1997)
www.sciencemag.org
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Nature is Inherently Patchy
Nature is inherently patchy, but anthropogenic
disturbanceoften results in landscapes different
from (and potentially less hospitable than) those
resulting from natural causes
Natural disturbance regime
Anthropogenic clearcut
500 yr
1000 yr
Images from Deutschman et al. (1997)
www.sciencemag.org
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Nature is Inherently Patchy
Nature is inherently patchy, but anthropogenic
fragmentation often results in landscapes
different from (and potentially less hospitable
than) those resulting from natural causes
Fragmentation reduces the extent and connectivity
of habitats
Fragmented landscapes typically have simplified
internal structure of patches and matrices
Fragmented landscapes typically have more
contrast between adjacent patches
Features of fragmented landscapes (e.g., roads
and dams) pose special threats to population
viability
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Patch (Fragment) Size and Isolation
Log10 (No. species)
Log10 (Area)
Data for Galapagos plants from van der Werff
(1983) Vegetatio
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Patch (Fragment) Size and Isolation
Data for Bismark Archipelago birds from Diamond
(1972) PNAS
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Patch (Fragment) Size and Isolation
Island Biogeography Theory emphasizes dynamism
patchiness of natural processes
Conservation Biologists (and managers) must
understand natural processes, to make sense of
anthropogenic disturbances and to restore
ecological / evolutionary processes
E. O. Wilson(b. 1929)
Robert MacArthur(1930-1972)
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Island Biogeography Theory
Concerns the dynamics of immigration from a
mainland source pool and extinction on islands or
patches surrounded by inhospitable matrix
Map on left from www.mapsofworld.com map on
right from www.peloncillo.org
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Island Biogeography Theory
Why does the immigration rate decline as a
function of S?
Immigration rate (e.g., new species per yr)
Number of species (S)
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Island Biogeography Theory
Why does the extinction rate increase as a
function of S?
Extinction rate (e.g., number of species per yr)
Number of species (S)
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Island Biogeography Theory
Immigration rate (e.g., new species per yr)
Turn-over rate (T)
Extinction rate (e.g., number of species per yr)
Equilibrium S
Number of species (S)
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Island Biogeography Theory
Why does the probability of immigration for each
species vary with island isolation?
Near island
Immigration rate (e.g., new species per yr)
Far island
TNear
TFar
Extinction rate (e.g., number of species per yr)
SNear
SFar
Number of species (S)
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Island Biogeography Theory
Why does the probability of extinction for each
species vary with island size?
Small island
Immigration rate (e.g., new species per yr)
Large island
TSmall
TLarge
Extinction rate (e.g., number of species per yr)
SLarge
SSmall
Number of species (S)
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Island Biogeography Theory
Small island
Near island
Immigration rate (e.g., new species per yr)
Far island
Large island
Extinction rate (e.g., number of species per yr)
SNear,Large
SFar,Small
SNear,SmallSFar,Large
Number of species (S)
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Single Large or Several Small (SLOSS) Debate
Ecological Assembly Rules
E.g., Sometimes we find nested subsets in which
larger areas contain the same subset of species
as smaller areas, plus additional area-sensitive
species
Jared Diamond(b. 1937)
From from Wikipedia
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Single Large or Several Small (SLOSS) Debate
Nested Subsets
A B
A B C D E
A B C
Jared Diamond(b. 1937)
Relaxation loss of species that occurs after
fragmentation event
If fragments contain nested subsets of species,
then a single large reserve is better than
several small ones of the same total area
From from Wikipedia
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Species especially vulnerable to fragmentation
Wide-ranging
Poor dispersal abilities
Specialized requirements
Low fecundity
Vulnerable to human exploitation or persecution
Cougar
Arctic tern
Desert pup fish
Coyote
Ground nut
Heliconius erato
Images from Wikipedia
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Lago Guri Islands, Venezuela
Not just relaxation, but devastating ecological
meltdown owing to top-down trophic cascades
Perturbation that propagates downward through two
or more trophic levels, resulting in alternating
positive and negative impacts on successive levels
John Terborgh(b. 1936)
Photo from www.env.duke.edu
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Top-down Trophic Cascades








Tree seedlings
Tree seedlings
Photos from Wikipedia
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Biological Dynamics of Forest Fragments Project
(BDFFP), Amazonas, Brazil
Thomas Lovejoy
Bill Laurance
Recipients of the 2009 BBVA Foundation Frontiers
of Knowledge Award in Ecology and Conservation
Biology
Photos from www.mongabay.com
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Biological Dynamics of Forest Fragments Project
(BDFFP), Amazonas, Brazil
Photo of a forest fragment, surrounded by newly
created cattle pasture in Brazil
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Biological Dynamics of Forest Fragments
NASA false-color remotely sensed image of the
confluence of Río Negro Río Solimões (Amazon)
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Biological Dynamics of Forest Fragments
NASA false-color remotely sensed image of BDFFP
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Biological Dynamics of Forest Fragments
Edge effects negative effects of a habitat edge
on interior conditions
Some species can only inhabit the interior or
core, and some are specifically attracted to the
edge
Figure from Laurance et al. (2006) PNAS
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Corridors
Corridors can help connect fragments
E.g., United Nations Educational, Scientific
Cultural Organization (UNESCO) World Heritage
Sites in the Wet Tropics of Queensland, Australia
Map from www.enviro-map.com
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Conservation Biologists (and managers) must
understand natural processes, to determine
conservation targets how to achieve them
Image from www.rewilding.org
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Conservation Biologists (and managers) must
understand natural processes, to determine
conservation targets how to achieve them
Image from www.rewilding.org
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Conservation Biologists (and managers) must
understand natural processes, to determine
conservation targets how to achieve them
Image from www.floridahabitat.org