Download Evolution

AP Environmental
Science
Mr. Grant
Lesson 27
Evolution, Biodiversity, and
Population Ecology
Evolution as the Wellspring of
Earth’s Biodiversity
© 2011 Pearson Education, Inc.
Objectives:
• Define the terms evolution and natural selection.
• Explain the process of natural selection and cite evidence
for this process.
• Describe the ways in which evolution influences
biodiversity.
• Discuss reasons for species extinction and mass
extinction events.
© 2011 Pearson Education, Inc.
Define the terms evolution and natural selection.
Evolution: Genetically based change in the appearance,
functioning, and/or behavior of organisms across
generations, often by the process of natural selection.
Natural Selection: The process by which traits that
enhance survival and reproduction are passed on more
frequently to future generations of organism than those
that do not, thus altering the genetic make-up of
populations through time. Natural selection acts on
genetic variation and is a primary driver of evolution.
© 2011 Pearson Education, Inc.
Striking gold in Costa Rica
• In 1964, Golden toads were
discovered in Monteverde,
Costa Rica
• The mountainous cloud
forest has a perfect climate
for amphibians
• They became extinct within
25 years
- Climate change’s drying
effect on the forest
- A lethal fungus
© 2011 Pearson Education, Inc.
Explain the process of natural selection and cite
evidence for this process.
• Because organisms produce excess young, individuals vary in
their traits, and many traits are inherited, some individuals will
prove better at surviving and reproducing. Their genes will be
passed on and become more prominent in future generations.
• Mutations and recombination provide the genetic variation for
natural selection.
• We have produced out pets, farm animals, and crop plants
through artificial selection.
© 2011 Pearson Education, Inc.
Evolution generates biodiversity
• Species = a population or group of populations
- Whose members share characteristics
- They can breed with one another and produce
fertile offspring
• Population = a group of individuals of a species that
live in the same area
• Evolution = means change over time
- Biological evolution: genetic change in
populations over time
- Genetic changes lead to changes in appearance,
functioning or behavior over generations
© 2011 Pearson Education, Inc.
Natural selection
• Evolution may be random
- Or directed by natural selection
• Natural Selection = traits that enhance survival and
reproduction
- Are passed on more frequently to future generations
- Than those that do not
© 2011 Pearson Education, Inc.
Evolution by natural selection
•
It is one of the best-supported and most illuminating concepts in all science
–
•
It is the standpoint of modern biology
We must understand it to appreciate environmental science
–
Knowing ecology and learning the history of life
•
Evolutionary processes influence pesticide resistance, agriculture, medicine,
health, etc.
•
In 1858, both Darwin and Wallace proposed natural selection as the mechanism of
evolution
© 2011 Pearson Education, Inc.
Natural selection shapes organisms
•
Premises of natural selection:
- Organisms struggle to survive and reproduce
- Organisms produce more offspring than can
survive
- Individuals of a species vary in their
characteristics due to genes and the environment
- Some individuals are better suited to their
environment and reproduce more effectively
• Natural selection acts on genetic variation
© 2011 Pearson Education, Inc.
Genetic variation
• Adaptation = the process where, over time,
characteristics (traits) that lead to better reproductive
success
- Become more prevalent in the population
• Adaptive trait (adaptation) = a trait that promotes
reproductive success
• Mutations = accidental changes in DNA that may be
passed on to the next generation
- Non-lethal mutations provide the genetic variation on
which natural selection acts
• Sexual reproduction also leads to variation
© 2011 Pearson Education, Inc.
Natural selection acts on genetic variation
• Natural selection changes
characteristics through:
• Directional selection =
drives a feature in one
direction
• Stabilizing selection =
favors intermediate traits
- Preserving the status quo
• Disruptive selection = traits
diverge in two or more
directions
© 2011 Pearson Education, Inc.
Environmental conditions affect selection
• Environmental conditions determine the pressures natural
selection exerts
- These pressures affect who survives and reproduces
- Traits evolve that allow success in that environment
• But traits that promote success at one time or place may
not do so at another
• Natural selection weeds out unfit individuals
- It also elaborates and diversifies traits that may
produce new species
© 2011 Pearson Education, Inc.
Selective pressures influence adaptation
• Related species in
different environments
- Experience different
pressures
- Evolve different traits
• Convergent evolution =
unrelated species may
evolve similar traits
- Because they live in
similar environments
© 2011 Pearson Education, Inc.
Evidence of natural selection is everywhere
• It is evident in every adaptation of every organism
• Artificial Selection = the process of selection
conducted under human direction
- Producing the great variety of dog breeds and food
crops
© 2011 Pearson Education, Inc.
Describe the ways in which evolution
results in biodiversity.
• Natural selection can act as a diversifying force as species adapt
to their environments in myriad ways.
• Speciation by geographic isolation (and other means) produces
new species.
• The branching patterns of phylogenetic trees reflect the historical
pattern by which lineages of organisms have diverged.
• The fossil record informs us about life’s history
© 2011 Pearson Education, Inc.
Evolution generates biological diversity
• Biological diversity (biodiversity) = the variety of life
across all levels of biological organization
- Species
- Genes
- Populations
- Communities
• Scientists have described 1.8 million species
- Up to 100 million species may exist
- Tropical rainforests are rich in biodiversity
© 2011 Pearson Education, Inc.
Speciation produces new types of organisms
• The process of generating new
species from a single species
• Allopatric speciation: species
formation due to physical
separation of populations
- The main mode of speciation
- Populations can be separated
by glaciers, rivers, mountains
- Each population gets its own
set of mutations
© 2011 Pearson Education, Inc.
Another type of speciation
• Sympatric speciation = species form from populations
that become reproductively isolated within the same area
- Feed in different areas
- Mate in different seasons
- Hybridization between two species
- Mutations
© 2011 Pearson Education, Inc.
Speciation results in diverse life forms
• How do major groups diverge over time?
• Phylogenetic trees (cladograms) = show
relationships among species, groups, genes, etc.
- Scientists can trace how certain traits evolved
© 2011 Pearson Education, Inc.
The fossil record
• Fossil: an imprint in stone of a dead organism
• Fossil record: the cumulative body of fossils worldwide
• The fossil record shows:
- Life has existed on Earth for at least 3.5 billion years
- Earlier types of organisms evolved into later ones
- The number of species has increased over time
- Most species have gone extinct
- There have been several mass extinctions in the past
© 2011 Pearson Education, Inc.
Discuss reasons for species extinction
and mass extinction events.
• Extinction may occur when species that are highly specialized or
that have small populations encounter rapid environmental
change.
• Earth’s life has experienced five known episodes of mass
extinction, which were due to asteroid impact and possibly
volcanism and other factors.
• Today, human impact may be initiating a sixth mass extinction.
© 2011 Pearson Education, Inc.
Extinction
• Extinction = the disappearance
of a species from Earth
- Species last 1-10 million
years
• Biological diversity is now
being lost at an astounding rate
- This loss of species is
irreversible
Number of species = speciation - extinction
© 2011 Pearson Education, Inc.
Extinction is a natural process, but …
• Humans profoundly affect rates of extinction
• Biodiversity loss affects people directly
- Food, fiber, medicine, ecosystem services
© 2011 Pearson Education, Inc.
Some species are more vulnerable to
extinction
• Extinction occurs when the environment changes rapidly
- Natural selection can not keep up
• Many factors cause extinction:
- Severe weather, climate change, changing sea levels
- New species, small populations
- Specialized species
• Endemic species = a species only exists in a certain,
specialized area
- Very susceptible to extinction
- These species usually have small populations
© 2011 Pearson Education, Inc.
Many U.S. amphibian species are vulnerable
• Many U.S. amphibians have very small ranges
- They are vulnerable to extinction
- The Yosemite toad, Houston toad, Florida bog frog
• 40 salamander species are restricted to areas the size of
a typical county
Some U.S. salamander species live on top of single mountains
© 2011 Pearson Education, Inc.
Earth has had several mass extinctions
• Background extinction rate = extinction usually occurs
one species at a time
• Mass extinction events = killed off massive numbers
of species at once
- Occurred five times in Earth’s history
- 50-95% of all species went extinct at one time
• Cretaceous-Tertiary (K-T) event: 65 million years ago
- Dinosaurs went extinct
• End-Permian event: 250 million years ago
- 75-95% of all species went extinct
© 2011 Pearson Education, Inc.
The sixth mass extinction is upon us
• Humans are causing the sixth mass extinction event
- Resource depletion, population growth, development
- Destruction of natural habitats
- Hunting and harvesting of species
- Introduction of non-native species
• It is 100-1,000 times higher than the background rate and
rising
• Amphibians are disappearing the fastest
- 170 species have already vanished
• It will take millions of years for life to recover
© 2011 Pearson Education, Inc.
The geologic record
© 2011 Pearson Education, Inc.
Macroevolution
© 2011 Pearson Education, Inc.