Upload
drake
View
47
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Habitat Fragmentation. - PowerPoint PPT Presentation
Citation preview
Habitat Fragmentation
Quote from David Quammen’s (1996) Song of the Dodo; Image from www.floridahabitat.org
"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 thirty-
six nice Persian throw rugs? No. All we're left with is three dozen ragged fragments, each one worthless and
commencing to come apart."
Photo of a fragmented Valdivian forest in Chile from: www.tncfire.org
Disturbance – a discrete event that removes biomass (and thereby can create heterogeneity or “patchiness”)
Habitat Fragmentation
Habitat fragmentation is an anthropogenic disturbance
Photo of a fragmented Valdivian forest in Chile from: www.tncfire.org
(2) A change in habitat configuration; remaining patches are smaller and more isolated than in the original configuration
with two components:
(1) A reduction in area of the focal habitat type
Habitat Fragmentation
Habitat fragmentation is an anthropogenic disturbance
Photo of Paul Keddy from www.drpaulkeddy.com; quote from Keddy’s (2008, pg. 14) Water, Earth, Fire
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)
Images from Deutschman et al. (1997); www.sciencemag.org
Natural disturbance
regime
500 yr 1000 yr
Green = Eastern hemlockPurple = American beech
Red = Red mapleYellow = Yellow birch
Nature is Inherently “Patchy” & Dynamic
Space-time Mosaic (Watt 1947); Shifting Mosaic (Bormann & Likens 1979); Patch Dynamics; Crazy Quilt (H. S. Horn)
500 yr 1000 yr
Images from Deutschman et al. (1997); www.sciencemag.org
Natural disturbance
regime
Anthropogenic clearcut
Nature is Inherently “Patchy” & Dynamic
Nature is inherently “patchy,” but anthropogenic disturbanceoften results in landscapes different from (and potentiallyless 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
Nature is Inherently “Patchy” & Dynamic
Nature is inherently “patchy,” but anthropogenic disturbanceoften results in landscapes different from (and potentiallyless hospitable than) those resulting from natural causes
Data for Galapagos plants from van der Werff (1983) Vegetatio
Log10 (Area)
Log 1
0 (N
o. s
peci
es)
Patch (Fragment) Size & Isolation
Data for Bismark Archipelago birds from Diamond (1972) PNAS
Patch (Fragment) Size & Isolation
E. O. Wilson(b. 1929)
Robert MacArthur(1930-1972)
Patch (Fragment) Size & Isolation
Conservation Biologists (and managers) must understand natural processes, to make sense of anthropogenic disturbances
and to restore ecological / evolutionary processes
Island Biogeography Theory emphasizes dynamism & patchiness of natural processes
Map on left from www.mapsofworld.com; map on right from www.peloncillo.org
Island Biogeography Theory
Concerns the dynamics of immigration from a mainland source pool and extinction on islands or patches
surrounded by inhospitable matrix
Immigration rate (e.g., new species
per yr)
Number of species (S)
Island Biogeography Theory
Why does the immigration rate decline as a function of S?
Extinction rate (e.g., number of species per yr)
Number of species (S)
Island Biogeography Theory
Why does the extinction rate increase as a function of S?
Immigration rate (e.g., new species
per yr)
Number of species (S)
Extinction rate (e.g., number of species per yr)
Turn-over rate (T)
Equilibrium S
Island Biogeography Theory
Immigration rate (e.g., new species
per yr)
Extinction rate (e.g., number of species per yr)
Near island
Far islandTNear
SNear
Number of species (S)
SFar
TFar
Island Biogeography Theory
Why does the probability of immigration for each species vary with island isolation?
Immigration rate (e.g., new species
per yr)
Extinction rate (e.g., number of species per yr)
Number of species (S)
Small island
Large islandTSmall
SLargeSSmall
TLarge
Island Biogeography Theory
Why does the probability of extinction for each species vary with island size?
Immigration rate (e.g., new species
per yr)
Extinction rate (e.g., number of species per yr)
Number of species (S)
Small island
Large island
Near island
Far island
SNear,Small
SFar,Large
SNear,LargeSFar,Small
Island Biogeography Theory
Ecological Assembly Rules
From from Wikipedia
Jared Diamond(b. 1937)
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
From from Wikipedia
Relaxation – loss of species that occurs after fragmentation event
A B C D E
A B
A B C
Single Large or Several Small (SLOSS) Debate
Jared Diamond(b. 1937)
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)
Images from Wikipedia
Arctic tern
Ground nutDesert pup fish
Heliconius erato
Cougar
Coyote
Species Especially Vulnerable to Fragmentation
Wide-ranging
Poor dispersal abilities
Specialized requirements
Low fecundity
Vulnerable to human exploitation or persecution
Photo from www.env.duke.edu
John Terborgh(b. 1936)
Perturbation that propagates downward through two or more
trophic levels, resulting in alternating positive and negative
impacts on successive levels
Lago Guri Islands, Venezuela
Not just relaxation, but devastating ecological meltdown owing to top-down trophic cascades
Photos from Wikipedia
– +
– +
++
– +
Tree seedlings Tree seedlings
Top-Down Trophic Cascades
Photos from www.mongabay.com
Thomas Lovejoy Bill Laurance
Recipients of the 2009 BBVA Foundation Frontiers of Knowledge Award in Ecology & Conservation Biology
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
Figure from Laurance et al. (2006) PNAS
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
Biological Dynamics of Forest Fragments Project (BDFFP), Amazonas, Brazil
Map from www.enviro-map.com
Corridors can help connect fragments
E.g., United Nations Educational, Scientific &
Cultural Organization (UNESCO) World
Heritage Sites in the Wet Tropics of Queensland,
Australia
Corridors
a
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
Conservation Biologists (and managers) must understand natural processes, to determine conservation targets
& how to achieve them