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Natural Selection and Species
Interactions
“Nature has given women so much power….”
- Samuel Johnson
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The Great Leap Forward
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Starting in 1958, Mao Zedong, leader of the
Communist Party of China, initiated a series
of policies to transform the country into a
modern, industrialized, communist society.
One of the first actions taken was known as
the Four Pests Campaign.
 This campaign sought to eliminate rats,
flies, mosquitoes, and sparrows.
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The Four Pests Campaign
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Masses of people were
mobilized to eradicate the
Eurasian Tree Sparrow.
Tactics included:
 Banging pots and pans,
preventing the birds from
landing, until they were
exhausted.
 Tearing down nests.
 Shooting them from the sky
using guns and sling shots.
“Everyone come and fight
sparrows.”
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Unintended Consequences
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The sparrows were hunted because they ate
grain seeds; reducing crop yields.
By April of 1960, Chinese leaders came to
realize that the sparrows also ate a large
number of pest insects, including locusts.
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Unintended Consequences
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The government made a series of other poor
agricultural decisions at this time, including:
 Ordering farmers to increase the density of
their planting by 6 times, believing that the
same species of plant would compete with
itself.
 Deeper plowing of the soil, which brought
up sand and rocks instead of more topsoil.
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The Great Famine
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The locust plague, overplanting, and
overplowing combined with a severe drought.
The number of victims is unknown, but
estimated between 20-43 million.
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Ecosystems: Everything is Connected
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An ecosystem is all of the organisms living
in an area.
Components of an ecosystem:
 Biotic Factors – Living and
once living parts of an
ecosystem.
- Ex: Plants, animals, dead
matter, waste
 Abiotic Factors – Nonliving
parts of an ecosystem.
- Ex: Water, rocks, light
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Organization of Life and the Environment
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Organism – An individual living thing.
Species – A group of organisms able to
breed and fertile offspring.
Population - All members of a species that
live in the same area at the same time.
Biological Community - All populations living
and interacting in an area.
Ecosystem - A biological community and its
physical environment.
Biosphere – All ecosystems in the entire
Earth.
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Ecosystem Organization
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What lives where, and why?
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Habitat – Where an organism lives
 Every organism a range of factors it can
survive in.
 Ex: Temperature, precipitation, etc.
Critical Factor - Single factor that is the most
critical in determining how species are
distributed – who lives in what habitat.
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Tolerance Limits
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Tolerance Limits - Minimum and maximum
levels beyond which a particular species
cannot survive or reproduce.
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Adaptation
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Adaptation – A trait that allows a species to
survive more easily and reproduce.
Evolution - Inheritance of specific genetic traits
that control adaptations, giving a species an
advantage in an environment.
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Natural Selection
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Natural Selection - Describes process where
better competitors survive and reproduce
more successfully.
Caused by:
 Random mutations – Changes in DNA are
usually bad, but can be beneficial.
 Selective pressure – Limited resources
mean only the best competitors survive.
 Sexual selection – Females choose a mate
based on certain characteristics.
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Natural Selection
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Artificial Selection
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The selective breeding of organisms by
humans for specific characteristics.
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Origin of Life
Modern humans
(Homo sapiens)
appear about
2 seconds
before midnight
Recorded human
history begins
1/4 second
before midnight
Origin of life
(3.6–3.8 billion
years ago)
Fig. 4-3, p.
Evidence of Evolution
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Physical Similarities
 Most animals have
similar bones in their
limbs (fins, arms, wings)
Comparing DNA
Vestigial Structures
 Still exist in the body but
are no longer needed
 Ex: Appendix, wisdom
teeth
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Factors Exerting Selective Pressure
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Physiological stress due to inappropriate
levels of a critical environmental factor.
 Moisture, Light, pH
Predation
 Organism is hunted and killed by another
 Includes parasites, bacteria, viruses
Competition
 Other organisms attempting to use same
resources
Luck
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Speciation
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Given enough time, enough mutations occur
that a new species develops from an old one.
 When are two groups considered a
different species?
- They cannot or will not interbreed to
produce healthy, fertile offspring.
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Natural Selection
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Speciation
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Divergent - Separation of one species into
new species.
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Speciation
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Convergent - Unrelated
organisms evolve to
look and act alike.
• Not related
• Caused by living in
similar environments
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Coevolution
The process of two species evolving in
response to long-term interactions with
each other.
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Same or Different Species?
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Animal Hybrids or New Species?
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More examples…
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The Taxonomic Naming System
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Crayfish
 a.k.a. Crawdad
 a.k.a. Spiny lobster
 a.k.a. Yabby
 a.k.a. Crawfish
 a.k.a. Creekcrab
 a.k.a. Mudbug
We need an
internationally
accepted name!
Scientific Naming System
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Based on the classification system.
Includes the organism’s genus and species
name.
 Genus is capitalized
 Species is lower case
 The scientific name is written in italics
Scientific name of the crayfish:
Procambarus clarkii
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The Taxonomic Naming System
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Divides organisms into different levels of
organization.
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Kingdom
Phylum
Class
Order
Family
Genus
Species
The more levels two organisms have in
common, the more related.
How related are they?
Canis lupus lupus
Canis familiaris
European Wolf
Domesticated dog
How related are they?
Archocentrus nigrofasciatus
Corvus splendens
Convict Cichlid
House Crow
Phylogenetic Tree
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Also known as a “tree of life”.
Organisms are grouped and classified based
on three characteristics:
 Physical characteristics
 DNA
 Behavioral characteristics
- Mating rituals, territorial, aggression, etc.
The more of these characteristics two
organisms have in common, the more
closely related they are according to
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evolution.
Phylogenetic Tree of Life
From left to
right:
1. Orangutan
2. Gorilla
3. Human
4. Chimpanzee
5. Bonobo
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Ecological Niche
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Habitat - Set of environmental
conditions in which a particular
organism lives.
Ecological Niche
- Description of role played by
a species in a biological
community.
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Specific Types of Niches
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Opportunistic Species - Quickly appear when
any opening in an ecosystem arises.
 Many weeds.
Pioneer Species – Able to quickly colonize
new ground where nothing else is growing.
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Types of Niches
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Keystone Species - A
species whose
impact on its
ecosystem is
especially large and
influential.
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SPECIES INTERACTIONS
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Predator-Prey
 Any organism that feeds directly on another
living organism is termed a predator.
- The organism that is eaten is the prey.
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Competition
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Intraspecific - Competition among members of
the same species.
 Dispersal
- Seeds sent far away from parent
 Territoriality
- Each individual defends part of ecosystem
 Resource Partitioning
- Adults and larvae eat different foods
 Ex: Caterpillars and butterflies
Interspecific - Competition between members of
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different species.
Resource Partitioning
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Symbiosis
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Symbiosis - Intimate living together of
members of two or more species.
 Commensalism - One member benefits
while other is neither benefited nor harmed.
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Mutualism - Both members benefit.
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Parasitism - One member benefits at the
expense of other.
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Example of Symbiosis
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Barnacles create homes by attaching themselves to
whales. The whales are unaffected.
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Example of Symbiosis
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Clownfish have a mucus coating that allows them
to live in sea anemones. Their presence attracts
other fish for the anemone to eat.
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Example of Symbiosis
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As bison walk through grass, insects are disturbed
and fly away. They are eaten by cowbirds.
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Example of Symbiosis
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Ostriches and gazelles feed next to each other.
Ostriches have excellent eyesight, while gazelles
have stronger senses of hearing and smell.
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Example of Symbiosis
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Mistletoe extracts water and nutrients from the
spruce tree directly.
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POPULATION DYNAMICS
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Population Growth
 Studies of population growth are based on
the idea of biotic potential.
 Biotic Potential - Potential of a population
to grow in the absence of limitations.
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Exponential Growth
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Exponential growth is graphed as a J curve.
 Carrying Capacity - Number of individuals
that can be indefinitely supported in a
given area.
- Overshoot - When a population
surpasses the carrying capacity of its
environment.
- Dieback – Population experiences a
sudden steep drop.
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Population Oscillations
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Growth to a Stable Population
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Logistic Growth - Growth occurs more slowly
as the population approaches carrying
capacity due to environmental resistance.
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Limiting Factors
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Environmental Resistance
 Any factor that slows the growth of a
population.
 Density-Dependent Factors – Most likely to
affect dense populations.
- Disease, Stress, Predation
 Density-Independent Factors – Affects
dense and diffuse populations evenly.
- Changes in climate, natural disasters
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Population Growth Strategies
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There are two main types of growth
strategies:
 K-strategists focus on long-term
development and a long life.
- Ideal for stable, predictable
environments.
 R-strategists focus on reproducing as
much and as quickly as possible.
- Ideal for risky, unstable environments.
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(r) Strategies
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Short life
Rapid growth
Early maturity
Many small offspring
Little parental care
Little investment in
individual offspring
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Adapted to unstable
environment
Pioneers, colonizers
Niche generalists
Prey
Regulated mainly by
extrinsic factors
Low trophic level
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(K) Strategies
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Long life
Slower growth
Late maturity
Fewer large
offspring
High parental care
and protection
High investment in
individual offspring
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Adapted to stable
environment
Later stages of
succession
Niche specialists
Predators
Regulated mainly by
intrinsic factors
High trophic level
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COMMUNITY PROPERTIES
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Primary Productivity - Rate of biomass
production. Used as an indication of the rate
of solar energy conversion to chemical
energy.
 Net Primary Productivity - Energy (amount
of biomass) left after respiration.
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Type of Strategist?
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Type of Strategist?
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Community Structure
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Randomly Arranged
 Individuals live wherever resources are
available.
Clumped
 Individuals cluster together for protection,
assistance, or resource access.
Regularly Arranged
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Community Structure
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