Download Handout #10 revised

The origin of species is the source of biological diversity
–Speciation, potentially in conjunction with extinction, is at the focal
point of evolution
Figure 14.1
What is a species?
– Similarities between some species and variation within a species can
make defining species difficult
The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
Figure 14.3D
The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
Other Species Concepts
–The morphological species concept
•Classifies organisms based on observable phenotypic traits
The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
Other Species Concepts
–The morphological species concept
•Classifies organisms based on observable phenotypic traits
–The ecological species concept
•Defines a species by its ecological role
–The phylogenetic species concept
•Defines a species as a set of organisms representing a specific
evolutionary lineage
The origin of species is the source of biological diversity
–Speciation, potentially in conjunction with extinction, is at the focal
point of evolution
Figure 14.1
Reproductive barriers keep species separate
– Reproductive barriers
• Serve to isolate a species’ gene pool and prevent interbreeding
• Are categorized as prezygotic or postzygotic
Table 14.3
Postzygotic barriers
– Operate after hybrid zygotes are formed
– One postzygotic barrier is hybrid sterility
• Where hybrid offspring between two species are sterile and
therefore cannot mate
Figure 14.3D
Table 14.3
Speciation
A. harrisi
A. leucurus
Figure 14.4
Speciation
A. harrisi
A. leucurus
Figure 14.4
A population is geographically divided, and new species often
evolve
Table 14.3
Evolution
Is evolution goal directed?
Is evolution goal directed?
Are Birds Really Dinosaurs with Feathers?
– Did birds evolve from dinosaurs?
– Evolutionary biologists
• Have been pondering this question for decades
Evolution
Mass extinctions were followed by diversification of life-forms
– Mass extinctions
• Occurred at the end of the Permian and Cretaceous periods
Great periods of adaptive radiation
One early theory suggested that as dinosaurs evolved into
larger and larger creatures they simply became too stupid
to survive.
The Cretaceous extinction, which included the dinosaurs
• May have been caused by an asteroid
The Cretaceous extinction, which included the dinosaurs
•Berkeley geologist named Walter Alvarez.
•a slender layer of red clay between the Late Cretaceous rock and the Paleocene
rock lying on top of it.
•contained thirty times the amount of the rare element iridium
The Cretaceous extinction, which included the dinosaurs
• May have been caused by an asteroid
•a collision between the earth and a gigantic asteroid rich in iridium
•the force of thousands of atomic bombs
•A dust cloud high into the sky.
•This cloud would block out nearly all of the sunlight, creating a long, cold,
unnatural winter, drastically changing the climate for years to come.
The Cretaceous extinction, which included the dinosaurs
• May have been caused by an asteroid
•a collision between the earth and a gigantic asteroid rich in iridium
•the force of thousands of atomic bombs
•A dust cloud high into the sky.
•This cloud would block out nearly all of the sunlight, creating a long, cold,
unnatural winter, drastically changing the climate for years to come.
•The few plants and animals that managed to survive, such as crocodiles and
early mammals, became the new rulers of a world without dinosaurs.
Other theories of extinction blame drastic changes in the environment.
•
Geological shifts may have caused critical changes in the earth's
atmosphere and consequentially the weather.
The formation of Pangaea
• Altered habitats and triggered extinctions
The separation of the continents
• Affected the distribution and diversification of organisms