Speciation and Extinction
Biogeography
October 29 - Nov 2
Speciation and Extinction



Defining a species

Morphological definition

Biological definition

Subspecies
Mechanisms of Speciation

Genetic drift

Natural selection

Gene flow
Types of Speciation

Allopatric speciation

Sympatric speciation


Other Issues

Convergent evolution

Parallel evolution

Coevolution

Punctuated equilibrium
Extinction

Probability of extinction

Recent extinctions

Fossil extinctions
Defining a Species
 Morphologically

Species are morphologically distinct
 Biologically

Reproductively isolated (geologically or biol)
 Subspecies

Populations that are morphologically (and
therefore presumably) genetically distinct
Mechanisms of Speciation

Genetic Drift



Natural Selection


Changes in genetic characteristics of population due
to pure chance
Founder Effect
Change in population (genetic/morphological)
resulting from expression of genetic characteristics by
individuals in population that enhances their survival
Gene Flow

Change in genetics of population due to introduction
of genetic materials from outside the population
Types of Speciation

Allopatric Speciation

occurs when pops are
geographically isolated so
gene flow b/w pops cannot
occur
• Vicariance events
• Disperal/Founder events
• Peripatric
Peripheral populations are
geog. isolated from main
population and thus genetic
divergence is accelerated
(form of Adaptive Radiation)

Types of Speciation
 Sympatric

Speciation
Speciation occurring within spatially contiguous
populations
• Parapatric

evolutionary divergence (speciation) in populations that occupy
different habitat in the same geographic area (sympatric form of
adaptive radiation)
• Chromosomal changes

Polyploidy in plants
Other Issues

Convergent Evolution

Unrelated species separated geographically evolve similar traits
Other Issues

Parallel Evolution

Descendants of an ancestor now isolated evolve in a similar fashion
Other Issues
 Coevolution

Mutualistic associations
 Punctuated


Equilibrium
Long periods with no change followed by severe
environmental changes
As compared to phyletic gradualism
Extinction

“ The ultimate fate of every species is extinction.”
Brown and Lomolino 2000

RED QUEEN HYPOTHESIS
“A species must continually evolve in order to keep
pace with an environment that is perpetually
changing, because all other species are evolving,
altering the availability of resources and the nature
of biotic interactions.”
Van Valen 1973
The Probability of Extinction
 Taxon





level
individuals
subspecies
species
more inclusive taxon levels
trophic cascades
The Probability of Extinction
 Ecological




Groups
Large body size
Upper trophic levels
Highly specialized
Specifc habitats
The Probability of Extinction

Population Size

Birth rates

Death rates

Carrying capacity

Small populations

Intrinsic demographic
events

Extrinsic ecological events

MVP = Minimum Viable
Population
The Probability of Extinction
Mice and Owl Populations
25,000
100
90
80
70
15,000
60
50
10,000
40
30
5,000
Number of owls
Number of mice
20,000
20
10
0
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23
Year
(Quammen 1996: Song of the Dodo, p. 295)
Recent Extinctions
 Passenger
 Barro
 Gray
Pigeon
Colorado Island
Whale
Fossil Extinctions
 Mass


extinctions
Permian-Triassic (225 mybp)
Pleistocene megafauna (10-12K ybp)
• Overkill hypothesis
• Climate hypothesis

Cretaceous-Tertiary (65 mybp)
Millenium Ecosystem Assessment 2005