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CHAPTER 12 EVOLUTION AND EXTINCTION
A TROPICAL
MURDER MYSTERY
Finding the missing birds of Guam
12
A TROPIAL MURDER MYSTERY
Finding the missing birds of Guam
At the end of this chapter you
will know:
• A variety of factors
influence natural selection
and contribute to
evolution.
• Factors that contribute to
endangerment of species.
Learning
Outcomes
12
A TROPIAL MURDER MYSTERY
Finding the missing birds of Guam
Main
Concept
TERMS TO KNOW:
Invasive species
Extinct/extinction
Extinction is part of natural
selection but the background
rate at present is several times
what we would expect of
nature.
Human action has contributed
to extinction around the world
in what is being called the
“sixth great extinction.”
The fifth extinction was 65
million years ago and included
dinosaurs.
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A TROPIAL MURDER MYSTERY
Finding the missing birds of Guam
TERMS TO KNOW:
Invasive species
Extinct/extinction
Case study: Beginning in the
late 1960s, indigenous bird
species began disappearing
from Guam. Within twenty
years, four species had
become extinct.
Scientists’ hypotheses about
the birds’ demise included
blood parasites and
pesticides. By asking local
people about the problem,
the answer came back—nonnative snakes.
Brown tree snake
Boiga irregularis
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Natural selection is the main mechanism by which
populations adapt and evolve
Within any population, some
individuals are better suited to
their environment than others.
Those with the “right stuff” will be
successful and reproduce.
This pressure from the
environment is non-random and
results in genes for specific
adaptations like coloration or size
becoming more common within a
population.
It is through this process of natural
selection of individuals that
populations evolve.
12
Natural selection is the main mechanism by which
populations adapt and evolve
Within any population, some
individuals are better suited to
their environment than others.
Those with the “right stuff” will be
successful and reproduce.
This pressure from the
environment is non-random and
results in genes for specific
adaptations like coloration or size
becoming more common within a
population.
It is through this process of natural
selection of individuals that
populations evolve.
12
Natural selection is the main mechanism by which
populations adapt and evolve
Within any population, some
individuals are better suited to
their environment than others.
Those with the “right stuff” will be
successful and reproduce.
This pressure from the
environment is non-random and
results in genes for specific
adaptations like coloration or size
becoming more common within a
population.
It is through this process of natural
selection of individuals that
populations evolve.
12
Natural selection is the main mechanism by which
populations adapt and evolve
Within any population, some
individuals are better suited to
their environment than others.
Those with the “right stuff” will be
successful and reproduce.
This pressure from the
environment is non-random and
results in genes for specific
adaptations like coloration or size
becoming more common within a
population.
It is through this process of natural
selection of individuals that
populations evolve.
12
Natural selection is the main mechanism by which
populations adapt and evolve
Within any population, some
individuals are better suited to
their environment than others.
Potential outcomes
of natural selection
Those with the “right stuff” will be
successful and reproduce.
This pressure from the
environment is non-random and
results in genes for specific
adaptations like coloration or size
becoming more common within a
population.
It is through this process of natural
selection of individuals that
populations evolve.
12
Natural selection is the main mechanism by which
populations adapt and evolve
Within any population, some
individuals are better suited to
their environment than others.
Potential outcomes
of natural selection
Those with the “right stuff” will be
successful and reproduce.
This pressure from the
environment is non-random and
results in genes for specific
adaptations like coloration or size
becoming more common within a
population.
It is through this process of natural
selection of individuals that
populations evolve.
12
Natural selection is the main mechanism by which
populations adapt and evolve
Within any population, some
individuals are better suited to
their environment than others.
Potential outcomes
of natural selection
Those with the “right stuff” will be
successful and reproduce.
This pressure from the
environment is non-random and
results in genes for specific
adaptations like coloration or size
becoming more common within a
population.
It is through this process of natural
selection of individuals that
populations evolve.
12
Natural selection is the main mechanism by which
populations adapt and evolve
Within any population, some
individuals are better suited to
their environment than others.
Those with the “right stuff” will be
Potential outcomes of
successful
and
reproduce.
natural selection:
Stabilizing
directional
This pressureselection,
from the
stability, disruptive selection
environment is non-random and
results in genes for specific
adaptations like coloration or size
becoming more common within a
population.
It is through this process of natural
selection of individuals that
populations evolve.
12
Populations need genetic diversity to evolve
TERMS TO KNOW:
Selective pressure
Adaptation
Natural selection
Genes
Evolution
Gene frequencies
Genetic diversity
Two or more species can put
pressure on one another like
a ratchet. As one
characteristic rises to
dominance in a species, other
species affected by the
characteristic will also
experience selective
Coevolution is the outcome when two species
provide the selective pressure that determines
the traits favored by natural selection.
12
Populations need genetic diversity to evolve
TERMS TO KNOW:
Selective pressure
Adaptation
Natural selection
Genes
Evolution
Gene frequencies
Genetic diversity
Two or more species can put
pressure on one another like
a ratchet. As one
characteristic rises to
dominance in a species, other
species affected by the
characteristic will also
experience selective
Coevolution is the outcome when two species
provide the selective pressure that determines
the traits favored by natural selection.
12
Populations need genetic diversity to evolve
The invasive brown tree
snake was well adapted to
successfully prey on Guam’s
birds, but the birds had never
faced a predator like this.
Without any natural
defenses, the birds
disappeared so quickly that it
was difficult to determine
the cause of their extinction.
By matching the pattern of
declining bird populations
with the reported
appearance of snakes,
researchers were able to
establish correlation.
Coevolution is the outcome when two species
provide the selective pressure that determines
the traits favored by natural selection.
12
Populations need genetic diversity to evolve
The invasive brown tree
snake was well adapted to
successfully prey on Guam’s
birds, but the birds had never
faced a predator like this.
Without any natural
defenses, the birds
disappeared so quickly that it
was difficult to determine
the cause of their extinction.
By matching the pattern of
declining bird populations
with the reported
appearance of snakes,
researchers were able to
establish correlation.
Coevolution is the outcome when two species
provide the selective pressure that determines
the traits favored by natural selection.
12
Populations need genetic diversity to evolve
The invasive brown tree
snake was well adapted to
successfully prey on Guam’s
birds, but the birds had never
faced a predator like this.
Without any natural
defenses, the birds
disappeared so quickly that it
was difficult to determine
the cause of their extinction.
By matching the pattern of
declining bird populations
with the reported
appearance of snakes,
researchers were able to
establish correlation.
Coevolution is the outcome when two species
provide the selective pressure that determines
the traits favored by natural selection.
12
Populations need genetic diversity to evolve
Coevolution is the outcome when two species
provide the selective pressure that determines
the traits favored by natural selection.
12
Populations can diverge into subpopulations or new
species
TERMS TO KNOW:
Extirpation
Genetic drift
Bottleneck effect
Founder effect
If some of the birds on Guam
had characteristics that
allowed them to evade the
snakes or if they had not been
restricted to an island, a few
might have survived to
reproduce. This new
population may have been able
to co-exsist with brown tree
snakes.
12
Populations can diverge into subpopulations or new
species
TERMS TO KNOW:
Extirpation
Genetic drift
Bottleneck effect
Founder effect
Genetic drift – Pure chance
and random mating can
increase or decrease the
frequency of a trait.
12
Populations can diverge into subpopulations or new
species
TERMS TO KNOW:
Extirpation
Genetic drift
Bottleneck effect
Founder effect
Bottleneck effect – Part of the
population dies suddenly,
leaving the survivors to
produce a new generation .
12
Populations can diverge into subpopulations or new
species
TERMS TO KNOW:
Extirpation
Genetic drift
Bottleneck effect
Founder effect
Founder effect – Small group
contains only some of the
original variants and becomes
isolated.
12
The pace of evolution is generally slow but is
responsive to selective pressures
TERMS TO KNOW:
Extirpation
Genetic drift
Bottleneck effect
Founder effect
In addition to genetic diversity,
the size of the population makes
a difference in how quickly
natural selection can produce a
change in population.
Beneficial traits can spread more
quickly in smaller populations
because the likelihood of mates
having similar traits is greater.
A Guam rail, a critically endangered species.
The species’ decline and status of “extinct in the
wild” was caused by the introduction of the
brown tree snake.
12
Extinction is normal, but the rate at which it is
currently occurring appears to be increasing
Extinction is a natural part
of evolution.
Estimates are that 99% of
all species that ever lived
on Earth have gone extinct.
There have been five major
extinction events, each
leading to the extinction of
50% or more of the species
present on Earth.
The current global population of humans has
triggered a sixth major extinction event—the
one of which we are in the midst.
TERMS TO KNOW:
Background rate of
extinction
Fossil record
12
Extinction is normal, but the rate at which it is
currently occurring appears to be increasing
Extinction is a natural part
of evolution.
Estimates are that 99% of
all species that ever lived
on Earth have gone extinct.
There have been five major
extinction events, each
leading to the extinction of
50% or more of the species
present on Earth.
The current global population of humans has
triggered a sixth major extinction event—the
one of which we are in the midst.
Terms to know:
Background rate of
extinction
Fossil record
12
Extinction is normal, but the rate at which it is
currently occurring appears to be increasing
Extinction is a natural part
of evolution.
Estimates are that 99% of
all species that ever lived
on Earth have gone extinct.
There have been five major
extinction events, each
leading to the extinction of
50% or more of the species
present on Earth.
The current global population of humans has
triggered a sixth major extinction event—the
one of which we are in the midst.
Terms to know:
Background rate of
extinction
Fossil record
12
Extinction is normal, but the rate at which it is
currently occurring appears to be increasing
Extinction is a natural part
of evolution.
Estimates are that 99% of
all species that ever lived
on Earth have gone extinct.
There have been five major
extinction events, each
leading to the extinction of
50% or more of the species
present on Earth.
The current global population of humans has
triggered a sixth major extinction event—the
one of which we are in the midst.
Terms to know:
Background rate of
extinction
Fossil record
12
Extinction is normal, but the rate at which it is
currently occurring appears to be increasing
Extinction is a natural part
of evolution.
Estimates are that 99% of
all species that ever lived
on Earth have gone extinct.
There have been five major
extinction events, each
leading to the extinction of
50% or more of the species
present on Earth.
The current global population of humans has
triggered a sixth major extinction event—the
one of which we are in the midst.
Terms to know:
Background rate of
extinction
Fossil record
12
Humans affect evolution in a number of ways
Artificial selection
works the same way as
natural selection, but
humans are the source
of selective pressure.
All dogs are descendants of
the wolf. By only breeding
those males and females
with the desired traits,
humans have created more
than 170 breeds
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Humans affect evolution in a number of ways
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Humans affect evolution in a number of ways
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Humans affect evolution in a number of ways
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Humans affect evolution in a number of ways
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PERSONAL CHOICES THAT HELP
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UNDERSTANDING THE ISSUE
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UNDERSTANDING THE ISSUE
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ANALYZING THE SCIENCE
Species extinction and human population
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EVALUATING NEW INFORMATION
The effects of the sixth mass extinction
on evolution:
www.actionbioscience.org/evolution/
myers_knoll.html
IUCN species of the day:
www.iucnredlist.org/species-of-theday/archives
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MAKING CONNECTIONS
www.iucnredlist.org
International Union for Conservation of Nature (IUCN)