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Lecture Outlines
Chapter 3
Environment:
The Science behind the
Stories
4th Edition
Withgott/Brennan
© 2011 Pearson Education, Inc.
This lecture will help you understand:
• Natural selection
• How evolution influences
biodiversity
• Reasons for species
extinction
• Ecological organization
• Population characteristics
• Population ecology
• Conserving biodiversity
© 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.
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
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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
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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
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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.
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
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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
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Macroevolution
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Ecology is studied at several levels
• Ecology and evolution are
tightly intertwined
• Biosphere = the total living
things on Earth
- And the areas they inhabit
• Community = interacting
species living in the same
area
• Ecosystem = communities
and the nonliving material
and forces they interact with
© 2011 Pearson Education, Inc.
Levels of ecological studies
• Population ecology = investigates the dynamics of
population change
- The factors affecting the distribution and abundance of
members of a population
- Why some populations increase and others decrease
• Community ecology = focuses on patterns of species
diversity and interactions
• Ecosystem ecology = studies living and nonliving
components of systems to reveal patterns
- Nutrient and energy flows
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Each organism has habitat needs
• Habitat = the environment where an organism lives
- It includes living and nonliving elements
• Habitat use = each organism thrives in certain
habitats, but not in others
- Results in nonrandom patterns of use
• Habitat selection = the process by which organisms
actively select habitats in which to live
- Availability and quality of habitat are crucial to an
organism’s well-being
- Human developments conflict with this process
© 2011 Pearson Education, Inc.
A specialized frog
• Epiphytes grow on trees for support
- Obtaining water from the air
- They collect pools of rainwater and pockets of leaf
litter
- Frogs lay their eggs in
these rainwater pools
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Habitats vary
• Habitats vary with the body size and needs of species
- A soil mite vs. an elephant
• Species have different habitat needs at different times
- Migratory birds use different habitats during
migration, summer and winter
• Species use different criteria to select habitat
- Soil, topography, vegetation, other species
- Water temperature, salinity, prey
• Species survival depends on having suitable habitat
© 2011 Pearson Education, Inc.
Organismal ecology: niche
• Niche = an organism’s use of resources
- Along with its functional role in a community
- Habitat use, food selection, role in energy and
nutrient flow, interactions with other individuals
• Specialists = have narrow niches and specific needs
- Extremely good at what they do
- But vulnerable when conditions change
• Generalists = species with broad niches
- They use a wide array of habitats and resources
- They can live in many different places
© 2011 Pearson Education, Inc.
Population characteristics
• All populations show
characteristics that help
scientists predict their
future dynamics
• Population size = the
number of individual
organisms present at a
given time
- Numbers can increase,
decrease, cycle or
remain the same
© 2011 Pearson Education, Inc.
Population characteristics
• Population density = the number of individuals in a
population per unit area
• Large organisms usually have low densities
- They need many resources and a large area to survive
• High densities make it easier to find mates
- But increase competition and vulnerability to predation
- Increased transmission of diseases
• Low densities make it harder to find mates
- But individuals enjoy plentiful resources and space
© 2011 Pearson Education, Inc.
Population characteristics
• Population distribution
(dispersion) = spatial
arrangement of organisms
• Random = haphazardly located
individuals, with no pattern
• Uniform = individuals are
evenly spaced
- Territoriality, competition
• Clumped = arranged according
to availability of resources
- Most common in nature
© 2011 Pearson Education, Inc.
Population characteristics
• Sex ratio = proportion of males to females
- In monogamous species, a 1:1 sex ratio maximizes
population growth
• Age distribution (structure) = the relative numbers
of organisms of each age in a population
- Age structure diagrams (pyramids) = show the age
structure of populations
• In species that continue growing as they age
- Older individuals reproduce more (i.e. a tree)
- Experience makes older individuals better breeders
© 2011 Pearson Education, Inc.
Birth and death rates
Survivorship curves = the likelihood of death varies with
age
• Type I: more deaths at older
ages
• Type II: equal number of
deaths at all ages
• Type III: more deaths at
young ages
© 2011 Pearson Education, Inc.
Four factors of population change
• Natality = births within the population
• Mortality = deaths within the population
• Immigration = arrival of individuals from outside the
population
• Emigration = departure of individuals from the
population
• Births and immigration add individuals
- Deaths and emigration remove individuals
• Crude birth (death) rates: number of births (deaths) per
1000 individuals per year
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Population growth rate
• Natural rate of population growth =
(Crude birth rate) – (crude death rate)
- Population change due to internal factors
• Population growth rate =
(Crude birth rate + immigration rate) – (Crude death rate
+ emigration rate)
- Net changes in a population’s size/1000/year
• Growth rate as a percent =
- Population growth rate * 100%
- Populations of different sizes can be compared
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Exponential population growth
• Exponential growth
- A population increases by a
fixed percent
- Graphed as a J-shaped
curve
• Exponential growth cannot
be sustained indefinitely
• It occurs in nature with a:
- Small population
- Low competition
- Ideal conditions
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Limiting factors restrain population growth
• Limiting factors = physical, chemical and biological
attributes of the environment
- They restrain population growth
• Environmental resistance = all limiting factors taken
together
- Stabilizes the population size
- Space, food, water, mates, shelter, suitable breeding
sites, temperature, disease, predators
- Aquatic systems: salinity, sunlight, temperature, etc.
© 2011 Pearson Education, Inc.
Carrying capacity
• Carrying capacity = the
maximum population size
of a species that its
environment can sustain
• Limiting factors slow and
stop exponential growth
- An S-shaped logistic
growth curve
Many factors contribute to environmental resistance and
influence a population’s growth rate and carrying capacity
© 2011 Pearson Education, Inc.
Population density impacts limiting factors
• Density-dependent factors = limiting factors whose
influence is affected by population density
- Increased density increases the risk of predation and
competition for mates
- Results in the logistic growth curve
- Larger populations have stronger environmental
resistance
• Density-independent factors = limiting factors whose
influence is not affected by population density
- Events such as floods, fires, and landslides
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Perfect logistic curves aren’t often found
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Carrying capacities can change
• Environments are complex and ever-changing
- Changing carrying capacities
• Humans lower environmental resistance for themselves
- Increasing our carrying capacity
- Technologies overcome limiting factors
• By increasing carrying capacity for humans
- We have reduced the carrying capacity for countless
other organisms
- Calling into question our own long-term survival
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Reproductive strategies vary among species
• Biotic potential = an organism’s capacity to produce
offspring
• K-selected species = species with long gestation periods
and few offspring
- Have a low biotic potential
- Stabilize at or near carrying capacity
- Good competitors
• r-selected species = species which reproduce quickly
- Have a high biotic potential
- Little parental care, populations fluctuate greatly
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Population changes affect communities
• As the population of one species declines, other species
may appear
• Human development displaces other species and threatens
biodiversity
• As Monteverde dried out, species disappeared
- Golden toads, harlequin frogs and more had been
pushed from their cloud-forest habitat into extinction
- 20 of 50 frog species, 2 lizard species went extinct
• Species from lower, drier habitats appeared
- 15 species tolerant of drier conditions had moved in
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Conserving biodiversity
• Human development, resource extraction and
population pressure are speeding changes
- In populations and communities
• Impacts threatening biodiversity have complex social,
economic and political roots
- We must understand these factors to solve problems
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Costa Rica and its environment
• Past economic and social forces still threaten Costa
Rica’s species and ecological communities
- Lush forests are seen as obstacles to agriculture and for
timber
- The country’s population grew to 3.34 million
- Pasture land increased from 12% to 33%
- Forests decreased from 80% to 25%
- Species were declining and becoming endangered
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Costa Rica’s species were in danger
• Few people saw the need to conserve biological resources
- Until it became clear they were being rapidly lost
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Costa Rica is protecting its environment
• The privately managed 10,500 ha (26,000 acre)
Monteverde Cloud Forest Reserve was founded in 1972
- To protect the forest, its plants and animals
• Costa Rica created the country’s first national parks and
protected areas in 1970
- Centered on areas of spectacular scenery
- Protecting valuable tropical dry forests, turtle nesting
beaches, coral reef systems
• Government support remains strong
- Over 25% of its land is under some type of protection
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Costa Rico’s protection is paying off
• Ecotourism: tourists visit protected areas
- Providing thousands of jobs and billions of dollars
to local economies
• But parks are still under-protected and underfunded
- Restoration is a step beyond preservation
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Conclusion
• The fundamentals of evolution and population ecology
are integral to environmental science
• Natural selection, speciation and extinction help
determine earth’s biodiversity
• Understanding how ecological processes function at the
population level is crucial to protecting biodiversity
© 2011 Pearson Education, Inc.
QUESTION: Review
Which of the following is NOT a part of the process of
natural selection?
a) Once grown, organisms generally don’t have to
struggle to survive
b) Organisms produce more young than can survive
c) Individuals vary in their genetic characteristics
d) Some individuals are better suited to their
environment than others
© 2011 Pearson Education, Inc.
QUESTION: Review
What happens as a result of adaptation?
a) Species have lower reproductive success and lower
survival.
b) Species have higher reproductive success and higher
survival.
c) Species have higher reproductive success and lower
survival.
d) Species have lower reproductive success and higher
survival.
© 2011 Pearson Education, Inc.
QUESTION: Review
Directional selection would result in which of the
following?
a) Dogs with black coats evolving whiter coats in colder
areas
b) Red and white flowers interbreeding, producing pink
flowers
c) Fish evolving bigger eyes as the water gets muddier
d) A population of birds, some with thicker beaks that
eat seeds, and others with thinner beaks that eat
insects
© 2011 Pearson Education, Inc.
QUESTION: Review
Allopatric speciation would occur in:
a) One population that mates in May, and another that
mates in June
b) Two populations separated by the Mississippi River
c) One population that feeds in tree branches, another
feeds on tree trunks
d) A population with a mutation that turns fur a different
color than usual
© 2011 Pearson Education, Inc.
QUESTION: Review
Which of these species is MOST vulnerable to extinction?
a) A species with a population size of 500 individuals
b) A species distributed in one county of the United
States
c) A species that eats many different plant species
d) A species that has hundreds of offspring
© 2011 Pearson Education, Inc.
QUESTION: Review
A community is defined as:
a) The total of living things on Earth
b) Members of the same population that can interbreed
c) Interacting species in an area
d) Species and the nonliving material they interact with
© 2011 Pearson Education, Inc.
QUESTION: Viewpoints
Should we care whether a species goes extinct?
a) Yes, because all life is important and valuable.
b) Yes, because we are causing this wave of
extinction, so we should fix it.
c) We should not, because it’s natural.
d) I don’t care; it really does not affect me.
© 2011 Pearson Education, Inc.
QUESTION: Viewpoints
Do you think humans are subject to limiting factors and,
ultimately, a fixed carrying capacity?
a) Yes, although we have raised the carrying capacity,
there are limits to the number of humans Earth can
support.
b) Yes, but technology will keep raising the carrying
capacity, so it’s not much of a problem.
c) No, humans are no longer constrained by
environmental limits, due to our technology and
ability to manipulate the environment.
d) I don’t care; it really does not affect me.
© 2011 Pearson Education, Inc.
QUESTION: Interpreting Graphs and Data
Which type of distribution is a
result of competition between
individuals?
a) Random
b) Uniform
c) Clumped
d) None of these
© 2011 Pearson Education, Inc.
QUESTION: Interpreting Graphs and Data
What does this graph
show?
a) The effects of
carrying capacity on
population growth
b) A population that
keeps growing
c) The effects of
exponential growth
d) The effects of
increasing carrying
capacity
© 2011 Pearson Education, Inc.