Lecture Outlines
Chapter 3
Evolution, Biodiversity, and Population Ecology
This lecture will help you understand:
Natural selection
How evolution influences biodiversity
Reasons for species extinction
Ecological organization
Population characteristics
Population ecology
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
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
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
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
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
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
Selective pressures from the environment
influence adaptation
Related species in different environments
experience different pressures and evolve different
traits
Convergent evolution
unrelated species may
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. This is also know
as Selective breeding. Agriculture was based on
this process.
Produced the great variety of dog breeds and food crops
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
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
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
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
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
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
Speciation and extinction together determine
Earth’s biodiversity
Human activity profoundly affects
rates
of extinction
Biodiversity loss affects people directly
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Populations may grow, shrink, or remain stable
Natality (reproduction) births within the population
Recruitment = number of births that live to reproduce.
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
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
Unregulated populations increase by
exponential growth
Doubling time = 70/growth rate %, this gives the time that is required for the population to double in size.
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
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
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
The logistic growth curve is a simplified model
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
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
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
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
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
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
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
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.
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.
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
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.
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.
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
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.
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.
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
QUESTION: Interpreting Graphs and Data
Which type of distribution is a result
of competition between individuals?
a) Random b) Uniform c) Clumped
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
