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Habitat Degradation & Loss
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Data for Galapagos plants from van der Werff (1983) Vegetatio
Species-Area Curves
No.
spe
cies
A very consistent pattern of organismal distribution
Area
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Data for Galapagos plants from van der Werff (1983) Vegetatio
Area
Log10 (Area)
No.
spe
cies
Log 1
0 (N
o. s
peci
es)
y = 30.4 • x0.31 R² = 0.78
ylog = (0.31 • xlog) + 1.5R² = 0.78
Log10(y) = Log10(30.4 • x0.31)
ylog = Log10(30.4) + (0.31 • Log10(x))
Species-Area Curves
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Map from www.stri.org; Photo by Christian Ziegler from www.nytimes.com
Barro Colorado Island
Species-Area Curves
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Data from the 50-ha Forest Dynamics Plot on Barro Colorado Island, Panama
Area
Log10 (Area)
No.
spe
cies
Log 1
0 (N
o. s
peci
es)
Species-Area Curves
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Whittaker rank-abundance curve
Data from the 50-ha Forest Dynamics Plot on Barro Colorado Island, Panama
Rank
Log 1
0 (N
o. in
divi
dual
s)
Most species are rare!
Relative-Abundance Distributions
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See: Rabinowitz et al. (1986) in Soulé, ed., Conservation Biology
X X
X
X X
X X
Wide Narrow
Habitat specificity
Broad Restricted Broad Restricted
Local population
size
Somewherelarge
Everywheresmall
Seven Forms of Rarity
Most species are rare, but rarity can be defined in various ways
Geographic distribution
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Rare species are especially vulnerable
Small populations are especially prone to extinction from both deterministic and stochastic causes
Image of extinct Hawai’i ’Ō’ō (Moho nobilis) from Wikipedia
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E.g., Hawaii’s native bird species Half of the
remaining species went extinct soon
after Captain James Cook arrived
(in 1778)
Half went extinct soon after the
Polynesians arrived (in ~ 300 A.D. / C.E.)
Image of extinct Hawai’i ’Ō’ō (Moho nobilis) from Wikipedia
Rare species are especially vulnerable
Small populations are especially prone to extinction from both deterministic and stochastic causes
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∆N
∆t= B - D
Rare species are especially vulnerable
In a closed population (i.e., no immigration or emigration) of size N, the change in population size for a change in time, where
B = births, and D = deaths, is:
Small populations are especially prone to extinction from both deterministic and stochastic causes
Remember the “BIDE factors”: birth, immigration, death & emigration
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∆N
∆t= b(N) – d(N)
∆N
∆t= (b-d)(N)
Rare species are especially vulnerable
Small populations are especially prone to extinction from both deterministic and stochastic causes
In a closed population (i.e., no immigration or emigration) of size N, the change in population size for a change in time, where
b = per capita birth rate, and d = per capita death rate, is:
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∆N
∆t= r(N)
If r>0, N grows; if r<0, N declines; if r=0, N does not change
Rare species are especially vulnerable
Small populations are especially prone to extinction from both deterministic and stochastic causes
Substitute r for (b-d), wherer = per capita growth rate:
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Example, r = –0.5 :
Population A Population BNA,t = 1000 NB,t = 10
NA,t+1 = 500 NB,t+1 = 5
Nt+1 = Nt + ∆N
∆t
Rare species are especially vulnerable
Small populations are especially prone to extinction from both deterministic and stochastic causes
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Deterministic r < 0
Genetic stochasticity
Demographic stochasticity individual variability of r (e.g., variance)
Environmental stochasticity temporal fluctuations of r (e.g., change in mean)
Catastrophes
Rare species are especially vulnerable
Small populations are especially prone to extinction from both deterministic and stochastic causes
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Demographic & Environmental Stochasticity
Demographic Stochasticity
Each student is a sexually reproducing, hermaphroditic, out-crossing annual plant.
In the first growing season (generation), each student mates (if there is at least 1 other individual in the population) and produces 2 offspring. Offspring have a
50% chance of surviving to the next season. Flip a coin for each offspring; “head” = lives, “tail” = dies. Note that average r = 0; each parent adds 2 births to the population and on average subtracts 2 deaths [self & 1 offspring – since
50% of offspring live and 50% die] prior to the next generation.
In a large pop. (e.g., whole class), heads and tails average out to give r=0 (no change in pop. size). When class is sub-divided into small sub-populations (e.g., 2 individuals each with no migration), some will have less than 2 live individuals after the coins are flipped to determine survivorship to the next
growing season (the next generation).
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Habitat Destruction, Loss, Degradation…
At least 83% of the Earth’s land surface has been transformed by human activities
(Sanderson et al. 2002)
About 60% of Earth’s ecosystems are considered degraded or unsustainably used
(Millennium Ecosystem Assessment 2005)
98% of U.S. streams and rivers have been fragmented (see next lecture) by dams
(Benke 1990)
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Habitat Destruction, Loss, Degradation…
Habitat degradation – impacts that affect many, but not all species; some of which may be temporary
Habitat destruction & loss – impacts that affect nearly all species; time scale for recovery is very long
How do humans destroy & degrade habitats & ecosystems?E.g., agricultural activities, extraction activities,
certain kinds of development
These are often considered to be the most important direct threats to biodiversity, since they eliminate species, reduce population sizes,
and reduce performance of individuals
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Image of shrinking forest cover on Borneo from www.planttreesaveplanet.com
Habitat Destruction, Loss, Degradation…
Loss of forest habitat in Borneo
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Image of Louisiana land loss (historical & projected;1932 - 2050) from www.lacoast.gov
Habitat Destruction, Loss, Degradation…
Loss of terrestrial coastal habitats in Louisiana
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Map from www.npr.org
Habitat Destruction, Loss, Degradation…
Degradation of marine and coastal habitats in Louisiana
Deepwater Horizon – drilling rig explosion on April 20, 2010
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Halpern et al. (2008) Science; see www.nceas.ucsb.edu
Habitat Destruction, Loss, Degradation…
Anthropogenic degradation of oceans
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Images from www.nasa.gov
Minimum sea ice concentration; 9% decline per decade
1979 2003
Habitat Destruction, Loss, Degradation…
Loss of ice from polar ice cap
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Pollution is a Form of Habitat Degradation
Light pollution
Air pollution & acid rain
Solid waste & plastics
Chemical pollution (e.g., DDT, endocrine disruptors)
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Photo from Wikipedia
Pollution is a Form of Habitat Degradation
Rachel Carson(1907 – 1964)
Silent Spring (1962) – motivated creation of the U.S. Environmental Protection Agency
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Image from www.time.com
Pollution is a Form of Habitat Degradation
Theo Colborn(b. 1927)
Theo Colborn, Dianne Dumanoski & John P. Meyers (1997) Our Stolen Future: How We Are Threatening Our Fertility, Intelligence and Survival
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Pollution is a Form of Habitat Degradation
Light pollution
Air pollution & acid rain
Solid waste & plastics
Chemical pollution (e.g., DDT, endocrine disruptors)
Excessive nitrogen inputs
Eutrophication
Etc…
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Image from www.gulfhypoxia.net
Pollution is a Form of Habitat Degradation
Excessive nitrogen inputs & eutrophication
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Image from www.lacoast.gov
Pollution is a Form of Habitat Degradation
Excessive nitrogen inputs & eutrophicationcontribute to coastal hypoxia (i.e., the “dead zone” phenomenon)
every summer off Louisiana’s coast
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Figure from Myers et al. (2000, Nature)
Biodiversity HotspotsUsually defined by species richness, endemism & threats
These hotspots of biodiversity cover only ~1.5% of the Earth’s land;if they were destroyed ~1/3 of Earth’s species would go extinct
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Map from www.fao.org
Biodiversity HotspotsUsually defined by species richness, endemism & threats
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Image of oiled pelicans on June 3, 2010 from the Gulf of Mexico from Wikipedia
Biodiversity Crisis
Whether or not habitat degradation or loss occurs in a biodiversity hotspot, any resulting biodiversity losses contribute to the global phenomenon, since
local losses aggregate to produce the global crisis.