ENVIRONMENTAL SCIENCE 13e
CHAPTER 4:
Biodiversity and
Evolution
Core Case Study: Why Are
Amphibians Vanishing? (1)
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Habitat loss and fragmentation
Prolonged drought
Increased ultraviolet radiation
Parasites
Viral and fungal diseases
Core Case Study: Why Are
Amphibians Vanishing? (2)
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Pollution
Climate change
Overhunting
Nonnative predators and competitors
33% of all amphibian species face
extinction
4-1 What Is Biodiversity and
Why Is It Important?
• Concept 4-1 The biodiversity found in
genes, species, ecosystems, and
ecosystem processes is vital to
sustaining life on earth.
Biodiversity (1)
• Species diversity
• A set of individuals that can mate and
produce fertile offspring
• 8-100 million species total; likely 1014 million
• 2 million species identified
• ~50% in endangered tropical
rainforests
Biodiversity (2)
• Genetic diversity
• Ecosystem diversity
– Biomes
• Distinct climate
• Certain species, especially vegetation
• Functional diversity
Science Focus: Insects
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Around for ~400 million years
Bad reputation
Useful to humans and ecosystems
Vital roles in sustaining life
– Pollinators
– Natural pest control
– Renewing soils
4-2 How Does the Earth’s Life
Change over Time?
• Concept 4-2A The scientific theory of
evolution explains how life on earth
changes over time through changes in the
genes of populations.
• Concept 4-2B Populations evolve when
genes mutate and give some individuals
genetic traits that enhance their abilities to
survive and to produce offspring with
these traits (natural selection).
Theory of Evolution
• Fossils
– Mineralized and petrified remains
– Skeletons, bones, and shells
– Leaves and seeds
– Impressions in rocks
– Fossil record incomplete: ~1% of all
species
• Charles Darwin, On the Origin of
Species, 1859
Population Changes over Time
• Populations evolve by becoming
genetically different over time
• Genetic variability – mutations
– Random changes in DNA molecules in
genes
– Can occur spontaneously
– External agents: radiation
– Can create a heritable trait
Natural Selection
• Adaptive traits - genetically favorable
traits that increase the probability to
survive and reproduce
• Trait – heritable and lead to differential
reproduction
• Faced with environmental change
– Adapt through evolution
– Migrate
– Become extinct
Evolution through Natural
Selection Summarized
• Genes mutate, individuals are
selected, and populations evolve
such that they are better adapted to
survive and reproduce under existing
environmental conditions.
Adaptation through Natural
Selection Has Limits
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Humans unlikely to evolve and have skin
that’s not harmed by UV radiation
1. Desired trait must already be in the gene
pool.
2. Must have high reproductive capacity so
adaptive traits can be spread rapidly
Three Myths about Evolution
through Natural Selection Refuted
1. “Survival of the fittest” does not mean
“survival of the strongest”
2. Organisms don’t develop traits just
because they would be useful: giraffes
and long necks
3. There is no grand plan of nature to
create more perfectly adapted species –
no trend toward genetic perfection
Science Focus: How Did We
Become Such a Powerful Species?
• Key adaptations – also enabled us to
modify environment
– Opposable thumbs
– Walk upright
– Complex brains
• Transmit ideas to others
• Develop technologies to alter environment
Technology dominates earth’s life support
systems and NPP
4-3 How Do Geological Processes and
Climate Changes Affect Evolution?
• Concept 4-3 Tectonic plate
movements, volcanic eruptions,
earthquakes, and climate change
have shifted wildlife habitats, wiped
out large numbers of species, and
created opportunities for the evolution
of new species.
Plate Tectonics
• Locations of continents and oceans
determine earth’s climate
• Movement of continents allow species to
move and adapt
• Earthquakes and volcanoes affect
biological evolution by separating
populations of a species and allowing new
species to develop
Earth’s Long-Term Climate
Changes
• Cooling and warming periods – affect
evolution and extinction of species
– Change ocean levels and area
– Glaciers expanding and contracting
– Climate changes
• Opportunities for the evolution of new
species
• Many species go extinct
Science Focus: Earth is Just
Right for Life to Thrive
• Life needs a temperature range that
results in liquid water
• Earth’s orbit: right distance from sun
• Earth’s optimal gravity: keeps atmosphere
• Favorable temperature range over earth
history has promoted evolution and
biodiversity
• Favorable oxygen level in atmosphere
4-4 How Do Speciation, Extinction, and
Human Activities Affect Biodiversity?
• Concept 4-4 Human activities
decrease the earth’s biodiversity by
causing the premature extinction of
species and by destroying or
degrading habitats needed for the
development of new species.
Speciation
• Speciation
– One species splits into two or more
species that can no longer breed and
produce fertile offspring
• Geographic isolation
• Reproductive isolation
Science Focus: Changing
Genetic Traits
• Artificial selection
– Selective breeding: crossbreeding varieties
within same species to enhance desired traits
– Grains, fruits, vegetables, dogs, other animals
• Genetic engineering
– Add, delete, or alter DNA segments
– Add desirable genes from other species
– New drugs, pest-resistant plants
– Controversial
Extinction (1)
• Biological extinction
– Entire species gone
• Local extinction
– All members of a species in a specific area
gone
• Endemic species vulnerable to extinction
• Background extinction
• Speciation generally more rapid than
extinction
Extinction (2)
• Mass extinction
– Earth took millions of years to recover
from previous mass extinctions
• Balance between speciation and
extinction determines biodiversity of
earth
• Humans cause premature extinction
of species
Human Activities and Extinction
• Cause premature extinction of species
4-5 What Is Species Diversity
and Why Is It Important?
• Concept 4-5 Species diversity is a
major component of biodiversity and
tends to increase the sustainability of
some ecosystems.
Species Diversity
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Species richness
Species evenness
Varies with geographic location
Species richness declines towards
poles
Richness and Sustainability
• Hypothesis
– Does a community with high species
richness have greater sustainability and
productivity?
• Research suggests “yes”
4-6 What Roles Do Species
Play in an Ecosystem?
• Concept 4-6 Each species plays a
specific ecological role called its
niche.
Ecological Niche (1)
• Species occupy unique niches and play
specific roles in an ecosystem
• Includes everything required for survival
and reproduction
– Water
– Sunlight
– Space
– Temperatures
– Food requirements
Ecological Niche (2)
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Generalist species
Specialist species
Native species
Nonnative species
– Spread in new, suitable niches
Science Focus: Cockroaches
• Existed for 350 million years – 3,500
known species
• Highly adapted, rapidly producing
generalists
– Consume almost anything
– Endure food shortage
– Survive everywhere except polar regions
– Avoid predation
• Carry human diseases
Indicator Species
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Early warning system
Fish
Birds
Butterflies
Amphibians
Keystone Species
• Significant role in their food web:
large affect on types and abundances
of other species in an ecosystem
• Elimination may alter structure and/or
function of ecosystem
• Pollinators
• Top predators
Foundation Species
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Create habitats and ecosystems
Beavers
Elephants
Seed dispersers
Science Focus: American
Alligator
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Highly adaptable
Only natural predator is humans
1967 – endangered species list
Successful environmental comeback
Keystone species
Case Study: Why Should We
Protect Sharks?
• Remove injured, sick animals
• Many are gentle giants
• Provide potential insight into cures for
human diseases such as cancer
• Keystone species
• Hunted and killed by humans
Three Big Ideas from This
Chapter - #1
• Populations evolve when genes
mutate and give some individuals
genetic traits that enhance their
abilities to survive and to produce
offspring with these traits (natural
selection).
Three Big Ideas from This
Chapter - #2
• Human activities are decreasing the
earth’s vital biodiversity by causing
the premature extinction of species
and by disrupting habitats needed for
the development of new species.
Three Big Ideas from This
Chapter - #3
• Each species plays a specific
ecological role in the ecosystem
where it is found (ecological niche).