CHAPTER 12 EVOLUTION AND EXTINCTION

A TROPICAL MURDER MYSTERY

Finding the missing birds of Guam

A TROPIAL MURDER MYSTERY Finding the missing birds of Guam12

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

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.

Main Concept

A TROPIAL MURDER MYSTERY Finding the missing birds of Guam12

TERMS TO KNOW:Invasive speciesExtinct/extinction

Case study: Beginning in the late 1960s, indigenous bird species began disappearing from Guam. Within twenty

years, four species had become extinct.

A TROPIAL MURDER MYSTERY Finding the missing birds of Guam12

TERMS TO KNOW:Invasive speciesExtinct/extinction

Scientists’ hypotheses about the birds’ demise included

blood parasites and pesticides. By asking local

people about the problem, the answer came back—non-

native snakes.

Brown tree snake Boiga irregularis

Natural selection is the main mechanism by which populations adapt and evolve12

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.

Natural selection is the main mechanism by which populations adapt and evolve12

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.

Natural selection is the main mechanism by which populations adapt and evolve12

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.

Natural selection is the main mechanism by which populations adapt and evolve12

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.

Natural selection is the main mechanism by which populations adapt and evolve12

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.

Potential outcomes of natural selection

Natural selection is the main mechanism by which populations adapt and evolve12

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.

Potential outcomes of natural selection

Natural selection is the main mechanism by which populations adapt and evolve12

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.

Potential outcomes of natural selection

Natural selection is the main mechanism by which populations adapt and evolve12

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.

Potential outcomes of natural selection: Stabilizing

selection, directional stability, disruptive selection

Populations need genetic diversity to evolve12TERMS TO KNOW:Selective pressureAdaptationNatural selectionGenesEvolutionGene frequenciesGenetic diversityTwo 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 pressure.

Coevolution is the outcome when two species provide the selective pressure that determines

the traits favored by natural selection.

Populations need genetic diversity to evolve12TERMS TO KNOW:Selective pressureAdaptationNatural selectionGenesEvolutionGene frequenciesGenetic diversityTwo 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 pressure.

Coevolution is the outcome when two species provide the selective pressure that determines

the traits favored by natural selection.

Populations need genetic diversity to evolve12

Coevolution is the outcome when two species provide the selective pressure that determines

the traits favored by natural selection.

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.

Populations need genetic diversity to evolve12

Coevolution is the outcome when two species provide the selective pressure that determines

the traits favored by natural selection.

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.

Populations need genetic diversity to evolve12

Coevolution is the outcome when two species provide the selective pressure that determines

the traits favored by natural selection.

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.

Populations need genetic diversity to evolve12

Coevolution is the outcome when two species provide the selective pressure that determines

the traits favored by natural selection.

Populations can diverge into subpopulations or new species12

TERMS TO KNOW:ExtirpationGenetic driftBottleneck effectFounder 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.

Populations can diverge into subpopulations or new species12

TERMS TO KNOW:ExtirpationGenetic driftBottleneck effectFounder effect

Genetic drift – Pure chance and random mating can increase or decrease the frequency of a trait.

Populations can diverge into subpopulations or new species12

TERMS TO KNOW:ExtirpationGenetic driftBottleneck effectFounder effect

Bottleneck effect – Part of the population dies suddenly, leaving the survivors to produce a new generation .

Populations can diverge into subpopulations or new species12

TERMS TO KNOW:ExtirpationGenetic driftBottleneck effectFounder effect

Founder effect – Small group contains only some of the original variants and becomes isolated.

The pace of evolution is generally slow but is responsive to selective pressures12

TERMS TO KNOW:ExtirpationGenetic driftBottleneck effectFounder 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.

Extinction is normal, but the rate at which it is currently occurring appears to be increasing12

TERMS TO KNOW:Background rate of extinctionFossil record

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.

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.

Extinction is normal, but the rate at which it is currently occurring appears to be increasing12

Terms to know:Background rate of extinctionFossil record

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.

Extinction is normal, but the rate at which it is currently occurring appears to be increasing12

Terms to know:Background rate of extinctionFossil record

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.

Extinction is normal, but the rate at which it is currently occurring appears to be increasing12

Terms to know:Background rate of extinctionFossil record

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.

Extinction is normal, but the rate at which it is currently occurring appears to be increasing12

Terms to know:Background rate of extinctionFossil record

Humans affect evolution in a number of ways12All dogs are descendants of the wolf. By only breeding

those males and females with the desired traits,

humans have created more than 170 breeds

Artificial selection works the same way as natural selection, but humans are the source of selective pressure.

Humans affect evolution in a number of ways12

Misconceptions

about Evolution

Humans affect evolution in a number of ways12

Misconceptions

about Evolution

Humans affect evolution in a number of ways12

Misconceptions

about Evolution

Humans affect evolution in a number of ways12

Misconceptions

about Evolution

PERSONAL CHOICES THAT HELP12

UNDERSTANDING THE ISSUE12

UNDERSTANDING THE ISSUE12

ANALYZING THE SCIENCE12Species extinction and human population

EVALUATING NEW INFORMATION12

www.actionbioscience.org/evolution/myers_knoll.html

www.iucnredlist.org/species-of-the-day/archives

The effects of the sixth mass extinction on evolution:

IUCN species of the day:

MAKING CONNECTIONS12

www.iucnredlist.orgInternational Union for Conservation of Nature (IUCN)