Lecture Outlines
Chapter 3
Evolution, Biodiversity, and
Population Ecology
Withgott/Laposata
Fifth Edition
© 2014 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
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Central Case Study: Saving Hawaii’s Native
Forest Birds
 Evolution in the Hawaiian Islands has generated
hundreds of species, many unique to the islands
 The island chain was once home to 140 species of
native birds
 In recent times, half of the native bird species have
gone extinct
 Introduced species (like pigs, cattle, rats, and cats)
destroyed habitat and killed eggs and young
 Avian malaria killed native birds at lower elevations
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Evolution: The Source of Earth’s 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 = change over time
 Biological evolution = change in populations of
organisms over generations
 Genetic changes lead to changes in appearance,
functioning, or behavior
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Evolution: The Source of Earth’s Biodiversity
 Genetic changes in evolution may be random
 But may be directed by natural selection
 Natural selection = process in which traits that
enhance survival and reproduction are passed on
more frequently to future generations than those that
do not
 Genetic makeup of future populations is changed
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Evolution: The Source of Earth’s Biodiversity
 Evolution is one of the best-supported and most
illuminating concepts in all science
 It is the foundation of modern biology
 We must understand it to appreciate environmental
science
 Understanding how species change over time and
adapt to their surroundings is crucial for
comprehending ecology and the history of life
 Evolutionary processes influence pesticide resistance,
agriculture, medicine, health, etc.
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Natural selection shapes organisms and
diversity
 In 1858, both Darwin and Wallace proposed natural
selection as the mechanism of evolution
 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
 Organisms with better adapted traits will produce
more offspring
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Natural selection shapes organisms and
diversity
 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
 Directional selection = drives a feature in one direction
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© 2014 Pearson Education, Inc.
Selective pressures from the environment
influence adaptation
 Related species in different environments
experience different pressures and evolve different
traits
 Convergent evolution = unrelated species may
acquire similar traits because they live in similar
environments
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© 2014 Pearson Education, Inc.
Evidence of natural selection is all around us
 It is evident in every adaptation of every organism
 Artificial selection = the process of selection
conducted under human direction
 Produced the great variety of dog breeds and food
crops
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© 2014 Pearson Education, Inc.
Evolution generates biodiversity
 Biological diversity (biodiversity) = the variety of
life across all levels of biological organization
 Species
 Genes
 Populations
 Communities
 Scientists have described 1.8 million species
 Estimates of the total number of species that exist
range from 3 million to 100 million
 Biodiversity exists nearly everywhere
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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
 Natural selection can speed the process
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© 2014 Pearson Education, Inc.
We can infer the history of life’s diversification
by comparing organisms
 How did the major groups of organisms come to be?
 Phylogenetic trees = diagrams that show
relationships among species, groups, genes, etc.
 Scientists can trace how certain traits evolved
 Some traits evolved and were passed on
 Other traits evolved more than once (e.g., the ability
to fly)
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© 2014 Pearson Education, Inc.
We can infer the history of life’s diversification
by comparing organisms
 Knowing how organisms are related to one another
helps scientists organize and name them
 Categories reflect evolutionary relationships
 Scientists use physical and genetic characteristics to
organize
 Each species gets a two-part Latinized scientific
name
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© 2014 Pearson Education, Inc.
The fossil record teaches us about life’s long
history
 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
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Speciation and extinction together determine
Earth’s biodiversity
 Extinction = the disappearance of a species from
Earth
 Species last 1–10 million years
 Extinction has historically been a natural occurrence
 The loss of a species is irreversible
Number of species in existence = speciation  extinction
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© 2014 Pearson Education, Inc.
Speciation and extinction together determine
Earth’s biodiversity
 Human activity profoundly affects rates of extinction
 Biodiversity loss affects people directly
 Food, fiber, medicine, ecosystem services
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© 2014 Pearson Education, Inc.
Some species are especially vulnerable to
extinction
 Extinction can occur when the environment changes
rapidly and natural selection can not keep up
 Many factors cause extinction:
 Severe weather, climate change, changing sea levels
 Arrival of new species
 Being a small population or specialized species
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Some species are especially vulnerable to
extinction
 Endemic species = a species that only exists in a
certain, specialized area
 Very susceptible to extinction
 Usually have small populations
 Island species are often endemic and thus at risk
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Some species are especially vulnerable to
extinction
 Many U.S. amphibians have very small ranges
 They are vulnerable to extinction
 For example, the Yosemite toad, Houston toad,
Florida bog frog
 Forty salamander species are restricted to areas the
size of a typical county
Some U.S. salamander species live on top
of single mountains
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Earth has seen several episodes of mass
extinctions
 Background extinction rate = a constant, slow rate of
extinction that occurs as a part of evolution
 Mass extinction events = episodes that killed off
massive numbers of species at once
 Occurred five times in Earth’s history
 50–95% of all species go 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
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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
 Today’s extinction rate is 100–1000 times higher
than the background rate and rising
 It will take millions of years for life to recover
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The Geologic Record
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Macroevolution
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We study ecology at several levels
 Ecology and evolution are tightly intertwined
 Biosphere = the total of living things on Earth and
the areas they inhabit
 Community = interacting species that live in the
same area
 Ecosystem = communities and the nonliving
material and forces they interact with
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© 2014 Pearson Education, Inc.
We study ecology at several levels
 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
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Each organism has habitat needs
 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
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Niche and specialization are key concepts in
ecology
 Niche = summary of everything an organism does
 Use of resources
 Functional role in a community: habitat use, food
selection, role in energy and nutrient flow, interactions
with other individuals
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Niche and specialization are key concepts in
ecology
 Specialists = species that have narrow niches and
specific needs
 Extremely good at what they do
 But vulnerable when conditions change
 Generalists = species with broad niches
 Use a wide array of habitats and resources
 Can live in many different places
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Population Ecology
 Population = individuals of a particular species that
inhabit an area
 Species may have different arrangements of their
populations
 Some populations (like the nēnē) exist as isolated
populations
 Others (like humans) exist as
large continuous populations
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Populations show characteristics that help
predict their dynamics
 Certain characteristics of a population help scientists
predict what will happen to them in the future
 Helps in managing threatened species
 Population size = number of individuals present at
a given time
 Populations generally grow when resources are
abundant and predators are few
 Decline in response to loss of resources, other
species, disasters
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© 2014 Pearson Education, Inc.
Population density
 Population density = the number of individuals in a
population per unit area
 High densities have advantages and disadvantages
 Easier to find mates
 Increased competition and vulnerability to predation
 Increased transmission of diseases
 Sometimes causes organisms to leave an area if too
dense
 Low densities provide access to plentiful resources
and space but make it harder to find mates
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Population distribution
 Population distribution (dispersion) = spatial
arrangement of organisms
 Random = haphazardly located individuals, with no
pattern
 Uniform = individuals are evenly spaced
 Territoriality, competition
 Clumped = organisms found close to other members
of population
 Most common in nature
 Clustering around resources
 Mutual defense
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© 2014 Pearson Education, Inc.
Sex ratio and age structure
 Sex ratio = proportion of males to females
 In monogamous species, a 1:1 sex ratio maximizes
population growth
 Most species are not monogamous, so ratios vary
 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 (e.g., a tree)
 Experience can help older individuals breed more
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Birth and death rates
 Survivorship curves = graphs that show that the
likelihood of death varies with age
 Type I: higher death rate at older ages
 Larger animals (e.g., humans)
 Type II: same death rate at all ages
 Medium-sized animals (e.g., birds)
 Type III: higher death rate at young ages
 Small animals, plants
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© 2014 Pearson Education, Inc.
Populations may grow, shrink, or remain stable
 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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Populations may grow, shrink, or remain stable
 Natural rate of population increase =
(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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Unregulated populations increase by
exponential growth
 Exponential growth = when a population increases
by a fixed percent
 Graphed as a J-shaped curve
 Exponential growth cannot be sustained indefinitely
 It occurs in nature with:
 Small population
 Low competition
 Ideal conditions
 Occurs often with introduced species
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© 2014 Pearson Education, Inc.
Limiting factors restrain population growth
 Limiting factors = physical, chemical, and
biological attributes of the environment that restrain
population growth
 Space, food, water, mates, shelter, suitable breeding
sites, temperature, disease, predators
 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
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© 2014 Pearson Education, Inc.
The influence of some factors depends on
population density
 Density-dependent factors = limiting factors whose
influence is affected by population density
 Increased density increases the risk of predation,
disease, and competition
 Results in the logistic growth curve
 Larger populations have stronger effects of limiting
factors
 Density-independent factors = limiting factors
whose influence is not affected by population density
 Events such as floods, fires, and landslides
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The logistic growth curve is a simplified model
 Few populations in nature match the curve exactly
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© 2014 Pearson Education, Inc.
Carrying capacities can change
 Environments are complex and ever-changing
 Limiting factors can change, altering the carrying
capacity
 Humans lower environmental resistance for
themselves
 Increases our carrying capacity
 Technologies overcome limiting factors
 In increasing carrying capacity for humans, we now
use immense portions of the planet’s resources
 We have reduced the carrying capacity for countless
other organisms
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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, few offspring, and strong parental care
 Have a low biotic potential
 Stabilize at or near carrying capacity; good competitors
 r-selected species = species that reproduce quickly
and offer little or no care for offspring
 Have a high biotic potential
 Populations fluctuate greatly
These are the two extremes—most species fall
somewhere in between
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Conserving Biodiversity
 Humans are developing land, extracting resources,
and growing as a population
 This increases the rate of environmental change for
other species
 Science can help us understand how we are
changing the environment
 Impacts threatening biodiversity have complex
social, economic, and political roots
 We must understand these factors to solve problems
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Introduced species pose challenges for native
populations and communities
 Some introduced species thrive in their new
environments, eliminating native species
 Native island species are particularly vulnerable
 Evolved in isolation with limited need for defenses
 Biologists and land managers often must eradicate
introduced species to protect native habitats
 In Hawaii, pigs are being hunted and pig-free areas
are being fenced off
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Innovative solutions are working
 Scientists, land managers, and private citizens are
protecting the native species and habitats of Hawaii
 Invasive species are being removed
 Native species (like the nēnē) are being protected,
and new populations are being started
 Ranch land is being restored to forest
 Coral reef communities are part of the largest
federally protected marine reserve in the world
 This restored and protected land has resulted in
ecotourism = the phenomenon of people visiting
the islands to experience the natural areas
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Climate change now poses an extra challenge
 Climate change is altering how we protect species
and habitats
 Land is typically protected to conserve the species
that live there
 As the climate changes, the protected land may no
longer support the same species
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
QUESTION: Review
Which of the following is NOT a part of the process of
natural selection?
a) Once grown, organisms generally do not 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.
© 2014 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.
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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
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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 and
another that feeds on tree trunks.
d) a population with a mutation that turns fur a different
color than usual.
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QUESTION: Review
Which of the following statements about extinction
is true?
a) Extinctions have only started now that humans are
changing the planet.
b) Extinction of one species never benefits any other
organisms in a community.
c) The vast majority of species that have ever existed
are now extinct.
d) Extinction rates stay at a constant background rate
and never change.
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QUESTION: Review
Which of these species is MOST vulnerable to
extinction?
a) A species whose crude death rate is lower than its
crude birth rate
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
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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.
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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.
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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.
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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
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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
© 2014 Pearson Education, Inc.