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Chapter 5
Evolution of Biodiversity
Earth is home to a tremendous
diversity of species
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Ecosystem diversity- the variety of
ecosystems within a given region.
Species diversity- the variety of species in
a given ecosystem.
Genetic diversity- the variety of genes
within a given species.
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Biological Diversity
Biological Diversity
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Number, variety and
variability of Earth’s
organisms- 1.9 million
identified
Consists of three
components:
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Genetic diversity (below)
Species
richness

Ecosystem
diversity
Functional Diversity The biological and
chemical processes such as energy flow
and matter recycling needed for the survival
of species, communities, and ecosystems.
Heat
Chemical
nutrients (carbon
dioxide, oxygen,
nitrogen,
minerals)
Heat
Solar
energy
Heat
Decomposers
(bacteria, fungi)
Heat
Ecological Diversity The
variety of terrestrial and
aquatic ecosystems
found
in an area or on the
earth.
Producers (plants)
Consumers
(plant eaters,
meat eaters)
Genetic Diversity The
variety
of genetic material within a
species or a population.
Heat
Species Diversity The number
and abundance of species
present in different communities. Fig. 4-2, p. 82
How Do New Species Evolve?
• Speciation: one species splits into two or more
species
• Geographic isolation: happens first; physical
isolation of populations for a long period
• Reproductive isolation: mutations and natural
selection in geographically isolated populations
lead to inability to produce viable offspring when
members of two different populations mate
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Species richness- the number of species in a
given area.
Species evenness- the measure of whether a
particular ecosystem is numerically
dominated by one species or are all
represented by similar numbers of
individuals.
Evolution is the mechanism
underlying biodiversity
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Evolution- a change in the genetic
composition of a population over time.
Microevolution- evolution below the
species level.
Macroevolution- Evolution which gives
rise to new species or new genera, family,
class or phyla.
Natural Selection = the process by which traits that enhance survival
and reproduction are passed on more frequently to future generations
than those that do not
Creating Genetic Diversity
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Genes- physical locations on chromosomes
within each cell of an organism.
Genotype- the complete set of genes in an
individual.
Mutation- a random change in the genetic
code.
Phenotype- the actual set of traits
expressed in an individual.
Evolution by artificial and natural
selection
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Evolution by artificial selection- when humans
determine which individuals breed.
Evolution by natural selection- the
environment determines which individuals
are most likely to survive and reproduce.
Darwin’s theory of evolution by
natural selection
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Individuals produce an excess of offspring.
Not all offspring can survive.
Individuals differ in their traits.
Differences in traits can be passed on from
parents to offspring.
Differences in traits are associated with
differences in the ability to survive and
reproduce.
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Evolution by Random Processes
Mutation- occur randomly and can add to the
genetic variation of a population.
Genetic drift- change in the genetic composition
of a population over time as a result of random
mating.
Bottleneck effect- a reduction in the genetic
diversity of a population caused by a reduction
in its size.
Founder effect- a change in a population
descended from a small number of colonizing
individuals.
Speciation and extinction
determine biodiversity
• Allopatric speciation- when new species are
created by geographic or reproductive
isolation.
• Sympatric speciation- the evolution of one
species into two species in the absence of
geographic isolation, usually through the
process of polyploidy, an increase in the
number of sets of chromosomes.
Sympatric 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
The pace of evolution
Evolution shapes ecological niches
and determines species distributions
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Range of tolerance- all species have an optimal
environment in which it performs well. The limit
to the abiotic conditions they can tolerate is
known as the range of tolerance.
Fundamental niche- the ideal conditions for a
species.
Niches
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Realized niche- the range of abiotic and biotic
conditions under which a species lives. This
determines the species distribution, or areas of the
world where it lives.
Niche generalist- species that live under a wide
range of conditions.
Niche specialist- species that live only in specific
habitats.
Adaptive Radiation
Emergence of
numerous species from
a common ancestor
introduced to new and
diverse environmentshappens when a niche
opens due to changes
Example:
Hawaiian
Honeycreepers
Natural selection acts on
genetic variation
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Directional selection = drives
a feature in one direction
Stabilizing selection =
produces intermediate traits,
preserving the status quo
Disruptive selection = traits
diverge in two or more
directions
If the environment changes, a trait may no longer be adaptive
Coevolution
•
Evolutionary change
One species acts as a selective force on a
second species
Inducing adaptations
that act as selective force on the first species
Example:
Wolf and Moose
Acacia ants and Acacia trees
Yucca Plants and Yucca moths
Lichen
1.
2.
2.
3.
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Convergent Evolution
Species from different evolutionary branches may
come to resemble one another if they live in very
similar environments
Example:
1. Ostrich (Africa) and Emu (Australia).
2. Sidewinder (Mojave Desert) and
Horned Viper (Middle East Desert)
Scientific Importance of Genetic
Diversity

Genetic Engineering
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Incorporation of genes from one organism into a different
species
Provided:
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New vaccines
More productive farm animals
Agricultural plants with desirable characteristics
Depends on genetic diversity (cannot create genes)
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Important to protect this diversity
Why we need diversity
 Example contributions to human life:
 Food
 Clothing
 Shelter
 Pollination of crops
 Antibiotics and medicines
 Biological processes (nitrogen
fixation)
Understanding evolution
is vital
• It alters the genetic makeup of a
population
• It is important for understanding antibiotic
and pesticide resistance, agricultural
issues, production, medicines, etc.
• Organisms adapt to their environment
and change over time
Evidence of Evolution
• 1. Biogeography
• 2. Fossil Record
• 3. Taxonomy
• 4. Homologous Structures
• 5. Comparative Embryology
• 6. Molecular Biology
The Fossil Record
• Fossils- remains of organisms that have
been preserved in rock. Much of what
we know about evolution comes from
the fossil record.
Science Focus: Species Richness
on Islands
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Species equilibrium model, theory of island
biogeography
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Rate of new species immigrating should balance with
the rate of species extinction
Island size and distance from the mainland need to be
considered
Edward O. Wilson
The Five Global Mass Extinctions
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Mass extinction- when large numbers of
species went extinct over a relatively
short period of time.
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Earth has had several mass
extinctions
Background extinction rate = extinction usually occurs
one species at a time
Mass extinction events = five events in Earth’s history that
killed off massive numbers of species at once
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50-95% of all species went extinct at one time
Humans are causing the sixth mass extinction event
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Resource depletion
Population growth
Development
Adaptive Radiation-- new species evolve during recovery
period following mass extinction
Mass Extinctions
Date of the
Extinction
Event
Percent
Species
Lost
65 mya
(million
years ago)
85
Dinosaurs, plants (except ferns and seed bearing
plants), marine vertebrates and invertebrates. Most
mammals, birds, turtles, crocodiles, lizards, snakes,
and amphibians were unaffected.
213 mya
44
Marine vertebrates and invertebrates
248 mya
75-95
Marine vertebrates and invertebrates
380 mya
70
Marine invertebrates
450 mya
50
Marine invertebrates
Species Affected
The Sixth Mass Extinction
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Scientists feel that we are in our sixth
mass extinction, occurring in the last two
decades.
Estimates of extinction rates vary widely,
from 2 % to 25% by 2020.
In contrast to previous mass extinctions,
scientists agree that this one is caused by
humans.
Characteristics of Endangered
Species
 Extremely small (localized) range
 Requiring a large territory
 Living on an island
 Having a low reproductive success
 Small population size
 Low reproductive rates
 Requiring specialized breeding areas
 Having specialized feeding habitats
Endangered & Extinct Species
Endangered & Extinct Species
Earth’s Biodiversity Hotspots
Causes of Loss of Biodiversity
• Habitat Loss
• Invasive species
• Climate change
• Pollution
• Overharvesting