Habitat Degradation & Loss

Data for Galapagos plants from van der Werff (1983) Vegetatio

Species-Area Curves

No.

spe

cies

A very consistent pattern of organismal distribution

Area

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

Map from www.stri.org; Photo by Christian Ziegler from www.nytimes.com

Barro Colorado Island

Species-Area Curves

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

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

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

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

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

∆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

∆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:

∆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:

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

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

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).

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)

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

Image of shrinking forest cover on Borneo from www.planttreesaveplanet.com

Habitat Destruction, Loss, Degradation…

Loss of forest habitat in Borneo

Image of Louisiana land loss (historical & projected;1932 - 2050) from www.lacoast.gov

Habitat Destruction, Loss, Degradation…

Loss of terrestrial coastal habitats in Louisiana

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

Halpern et al. (2008) Science; see www.nceas.ucsb.edu

Habitat Destruction, Loss, Degradation…

Anthropogenic degradation of oceans

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

Pollution is a Form of Habitat Degradation

Light pollution

Air pollution & acid rain

Solid waste & plastics

Chemical pollution (e.g., DDT, endocrine disruptors)

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

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

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…

Image from www.gulfhypoxia.net

Pollution is a Form of Habitat Degradation

Excessive nitrogen inputs & eutrophication

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

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

Map from www.fao.org

Biodiversity HotspotsUsually defined by species richness, endemism & threats

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.