SFSU- GEOGRAPHY 316:
BIOGEOGRAPHY (B. Holzman, PhD)
Lecture 12/6/02

Extinctions Today
I. Extinctions in recent time
 A) human population increase
 B) natural selection
II.  Who gets it
 A) r-selected vs. K-selected species
 B) loss of habitat
 C) loss of range
III.  Future
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I. Extinctions is recent time
Extinction is a biological reality:  It is a process of Evolution.
it is estimated that about 1/4 of the species of birds and mammals that have become extinct since 1600 A.D. may have died out naturally.

World Population:
1-2 MYA                   2-10 million
8000BC-1 A.D.    200-400 million
1 A.D.- 1750 A.D. 750 million
1750-1900                1.5 billion
1900-1965                3.0 billion
1990                        5.3 billion

12/02/02        6,259,793,164 click here to get a current number

Population continues to increase

Human population over time has correlated with species extinction

II Who gets it?
Types of strategies for organisms
Characteristics of r- selected organisms
small adults
many young
little - no parental care
early maturity
little to no immune system
short gestation
short lifespan
vulnerable to environmental change
population unstable
Boom and Bust cycle

Examples: rodents, bacteria, insects, rabbits, weeds,.......
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Characteristics of K selected organisms
larger adults
fewer young
parental care
slower maturity
slow rate of increase
long gestation
adapted to limited fluctuation in
environment
greater survivability
thermoregulation
immune system
longer lifespan
stable populations

Examples: big mammals i.e. big cats, wolves, elephants, whales, ? humans
    penguins. eagles, .....
 

Species can become extinct or endangered because of:
Excessive exploitation:  hunting
Introduced species: invasion
Environmental contaminants:  pollution
Habitat Destruction and Change:  this is the biggest contributor to current extinctions without replacement
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