Transcript Learning Goal

Learning Goal
Examine how life continues to evolve
within a changing environment
Speciation and extinction have
occurred throughout the Earth’s
history.
Speciation
The process of species formation from ancestral
populations.
Speciation rates can vary, especially when
adaptive radiation occurs when new habitats
become available
Adaptive radiation is the result of clusters of
closely related species that are each adaptively
specialized to a specific habitat or food source.
Extinction
Species extinction rates are rapid at time of
ecological stress.
There have been 5 major extinctions throughout
Earth’s history. They resulted in the loss of most
life on the planet
Some scientists believe we are in the midst of
the 6th extinction, this time due to human
impact.
The background extinction rate throughout
Earth’s history has been about 7-8 species per
year.
It is estimated that extinction rates are about
1000 times the background rate, with thousands
of species becoming extinct each year.
Speciation may occur when two populations
become reproductively isolated from each other.
Speciation results in a diversity of life forms.
Species can be physically separated by a
geographic barrier such as an ocean or a
mountain range, or various pre- and post-zygotic
mechanisms.
These can maintain reproductive isolation and
prevent gene flow.
Geographic Speciation
•
• Prezygotic Isolating
Mechanisms
Exert their effects before
the production of a zygote
(fertilized egg). There are
five types:
Ecological Isolation –
species live in the same
geographical region but
occupy different habitats.
Temporal Isolation –
Species live in the same
habitat but mate at
different times of the
year.
Behavioral Isolation –
Mating signals for one
species are not
recognized by another.
Mechanical Isolation –
Species have
differences between
reproductive organs or
other body parts.
Gametic Isolation –
There is a mismatch
between the sperm of
one species and the
eggs of another.
Postzygotic Isolating Mechanisms
Hybrid Inviability –
Hybrids (offspring of
mixed species) die as
embryos or at an early
age.
Hybrid Sterility –
Hybrids develop into
adults but cannot
reproduce.
Hybrid Breakdown –
First generation hybrids
are healthy and fertile,
but subsequent
breeding produce
chromosomal
abnormalities in future
generations.
New species arise from reproductive isolation
over time, which can involve scales of hundreds
of thousands or even millions of years.
Speciation can also occur rapidly through
mechanisms such as polyploidy in plants.
Populations of organisms continue to evolve.
Scientific evidence supports the idea that evolution
has occurred in all species and continues to occur.
Observable examples of evolution:
Chemical resistance to things like antibiotics and
pesticides.
Observed directional phenotypic change in a
population such as the Grant’s study of the finches
on the Galopagos.
Vocab Terms
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Speciation
Extinction
Background rate
Adaptive Radiation
Reproductive isolation
Geographic speciation
Temporal isolation
Behavioral isolation
Prezygotic isolating mechanisms
Postzygotic isolating mechanisms