Transcript ppt

Habitat Fragmentation
"Let's start indoors. Let's start by
imagining a fine Persian carpet and a
hunting knife. The carpet is twelve feet
by eighteen, say. That gives us 216
square feet of continuous woven
material. Is the knife razor sharp? If
not, we hone it. We set about cutting
the carpet into thirty-six equal pieces,
total them up--and find that, lo, there's
still nearly 216 square feet of
recognizably carpet like stuff. But what
does it amount to? Have we got thirtysix nice Persian throw rugs? No. All
we're left with is three dozen ragged
fragments, each one worthless and
commencing to come apart."
Quote from David Quammen’s (1996) Song of the Dodo; Image from www.floridahabitat.org
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
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
Nature is Inherently “Patchy” & Dynamic
“Water, earth, and fire are Louisiana’s three special ingredients…
The lowlands flood. The uplands burn… if you live in Louisiana,
there are only two possibilities: either your land will eventually flood,
or it will eventually burn. Most of our native plants and animals are
therefore dependent on either flooding or fire or, in some cases, both.”
Paul Keddy
(b. 1953)
Photo of Paul Keddy from www.drpaulkeddy.com; quote from Keddy’s (2008, pg. 14) Water, Earth, Fire
Nature is Inherently “Patchy” & Dynamic
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
Images from Deutschman et al. (1997); www.sciencemag.org
1000 yr
Nature is Inherently “Patchy” & Dynamic
Nature is inherently “patchy,” but anthropogenic disturbance
often results in landscapes different from (and potentially
less hospitable than) those resulting from natural causes
Natural
disturbance
regime
Anthropogenic
clearcut
500 yr
Images from Deutschman et al. (1997); www.sciencemag.org
1000 yr
Nature is Inherently “Patchy” & Dynamic
Nature is inherently “patchy,” but anthropogenic disturbance
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 (including patch-matrix juxtaposition)
Features of fragmented landscapes (e.g., roads and dams)
pose special threats to population viability
Log10 (No. species)
Patch (Fragment) Size & Isolation
3
2.5
2
1.5
1
0.5
0
-1
0
1
2
Log10 (Area)
Data for Galapagos plants from van der Werff (1983) Vegetatio
3
4
Patch (Fragment) Size & Isolation
Data for Bismark Archipelago birds from Diamond (1972) PNAS
Patch (Fragment) Size & 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
Robert MacArthur
E. O. Wilson
(1930-1972)
(b. 1929)
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
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)
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)
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)
Island Biogeography Theory
Why does the probability of immigration for each
species vary with island isolation?
Immigration rate
(e.g., new species
per yr)
Near island
Far island
TNear
TFar
Extinction rate
(e.g., number of
species per yr)
SFar
SNear
Number of species (S)
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)
SSmall
SLarge
Number of species (S)
Island Biogeography Theory
Immigration rate
(e.g., new species
per yr)
Extinction rate
(e.g., number of
species per yr)
Near island
Small island
Far island
Large island
SFar,Small
SNear,Small
SFar,Large
SNear,Large
Number of species (S)
Single Large or Several Small (SLOSS) Debate
Ecological Assembly Rules
Jared Diamond
(b. 1937)
From from Wikipedia
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
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 (SLOSS debate)
From from Wikipedia
Species Especially Vulnerable to Fragmentation
Wide-ranging
Poor dispersal abilities
Specialized requirements
Low fecundity
Vulnerable to human exploitation or persecution
Arctic tern
Cougar
Desert pup fish
Ground nut
Images from Wikipedia
Heliconius erato
Coyote
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
Top-Down Trophic Cascades
–
+
+
+
–
+
Tree seedlings
Photos from Wikipedia
–
+
Tree seedlings
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 & Conservation Biology
Photos from www.mongabay.com
Biological Dynamics of Forest Fragments Project
(BDFFP), Amazonas, Brazil
Photo of a forest fragment, surrounded by newly created cattle pasture in Brazil
Biological Dynamics of Forest Fragments Project
(BDFFP), Amazonas, Brazil
NASA false-color remotely sensed image of the confluence of Río Negro & Río Solimões (Amazon)
Biological Dynamics of Forest Fragments Project
(BDFFP), Amazonas, Brazil
NASA false-color remotely sensed image of BDFFP
Biological Dynamics of Forest Fragments Project
(BDFFP), Amazonas, Brazil
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
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
Conservation Biologists (and managers) must understand
natural processes, to determine conservation targets
& how to achieve them
Image from www.rewilding.org
Conservation Biologists (and managers) must understand
natural processes, to determine conservation targets
& how to achieve them
Image from www.rewilding.org