Transcript Speciation and Extinction - Downtown Magnets High School

Speciation and
Extinction
Big Idea 1: The process of Evolution
drives the diversity and unity of life
Essential Knowledge
• 1C1: Speciation and extinction have
occurred throughout the Earth’s history.
• 1C2: Speciation may occur when two
populations become reproductively
isolated from each other.
• 1C3: Populations in nature continue to
evolve.
Species
A group of individuals capable of
interbreeding and exchanging genetic
info to produce viable, fertile offspring.
NO Dog-Cat
Babies!
YES Panda
Babies!
Speciation
• Creation of a new species
• Usually occurs when 2 pops diverge from a
common ancestor
Speciation Can Be Slow….
• Very gradually, over a long time, the
population changes (gradualism). Change is
slow, constant, and consistent (Darwin).
Speciation Can Be Fast…
• Bursts of change followed by quiet periods
(Punctuated Equilibrium, Eldredge and
Gould, 1972)
What Could Cause Bursts??
• Sudden, quick changes in the environment
leads to more available niches!
Speciation is the reason for diversity of life!
Geographic
Isolation
Separation of pops by
a geographic barrier
exposes species to
new environmental
conditions.
TPS: What Other Items
May Be Geographic
Barriers?
Reproductive Isolation
• Biological factors (barriers) that stop 2 species
from producing viable, fertile offspring
• Can be pre/post zygotic barriers
Example: Polyploidy
• More than 1 set of chromosomes.
• Ex: Wheat: strains that are diploid (2
sets), tetraploid (4 sets) durum or macaroni
wheat, hexaploid (6 sets) bread wheat.
• Will not interbreed with each other.
Prezygotic Barriers
1.
2.
3.
4.
Goal: To impede
mating/fertilization!
Habitat isolation:
no/rare contact
Temporal isolation:
mate at diff. times of yr.
Behavioral isolation:
behavior mating rituals.
Mechanical isolation:
Morphological
differences
What Kind of Prezygotic Barrier is This?
Postzygotic Barriers
Goal: Prevent a hybrid zygote from being a
viable adult
• Frail/Weak Hybrids
• Sterile Hybrids
Extinction
• Occurs rapidly at times of ecological
stress.
Habitat Loss/ Habitat Fragmentation
Hunting/Poaching
Overfishing
5 Major Mass
Extinctions
On a Positive
Note..
• Extinction opens up available niches
(jobs) and leads to new species creation.
Evolution Continues to Occur…
• Activity in class…