Evolution and biodiversity occurred over billions of years as follows: - Chemical evolution began 4.7-4.8 billion years ago as life evolved on Earth. Biological evolution began around 2.3-2.5 billion years ago. - Species evolve over time through genetic mutations and natural selection, which can lead to microevolution within a population or macroevolution where new species are formed. - Biodiversity has increased through speciation as new species evolve but has also decreased due to extinction, both through natural causes and more recently by human impacts threatening many species.

1. Evolution & Biodiversity
Chapter 5

2. Origins of life
• Chemical analysis and
measurement of
radioactive elements
in rocks & fossils are
studied
• Evolution of life is
linked to evolution of
earth
• Life evolved over the
past 4.7 - 4.8 billion
years
• Chemical evolution
came first
• Biological evolution -
about 2.3 - 2.5 billion
years ago

3. Origins of Life
Chemical evolution
Biological evolution

4. How origins are studied
• Fossils
• Fossil record is uneven
and incomplete
• Why? Some organisms
left no fossils - some have
decomposed and some are
not yet found.
• It is believed we have
fossils representing about
1% of all organisms ever
living on earth
• Also use :
– chemical and radioactive
dating
– Ancient rocks
– Ice cores
– DNA from living organisms

5. Evolution & adaptation
• Within limits,
populations adapt to
changes in their
environment - called
biological evolution -
change in genetic
make-up in a
population through
successive generations
• POPULATIONS,
NOT INDIVIDUALS
EVOLVE BY
BECOMING
GENETICALLY
DIFFERENT.

6. • THEORY OF
EVOLUTION - all
species descended
from earlier, ancestral
species
• Microevolution
– Small genetic changes
that occur in a
population
• Macroevolution -
– Long-term, large-scale
evolutionary changes
among groups of
species - new species
are formed from
ancestral species and
other species are lost
through extinction.

7. Microevolution
• Development of
genetic variability in a
population
– Gene pool – set of all
genes in the individuals
of the population of a
species
• Alleles - genes have
two or more different
molecular kinds
• These are recombined
• Each member of
population gets
different combination
of alleles

8. Mutation
• Random change in structure of number of DNA
molecules in a cell
• Can occur in two ways:
– Exposure to external agents such as radioactivity, x-
rays, natural and man-made chemicals
– Random changes in coded genetic instructions.
Sometimes are beneficial and make survival easier under
existing or changing conditions.
Some are harmless and some are lethal.

9. • Mutations are:
– Random and unpredictable
– Only new source of genetic material
– Rare events

10. Mutation
• Random changes in structure or number of
DNA molecules in a cell
• Can be caused by radiation and chemicals -
mutagens
• Random mistakes
• Can occur in any cell but only passed on in
reproductive cells.

11. • Natural selection occurs when some
individuals have genetically based traits that
cause them to better survive and produce
offspring
• Idea developed by Charles Darwin in “On
the origin of the species by means of natural
selection”

12. More…
• Must be natural variability for a trait in a
population
• Trait must have a genetic bases that can be
passed from one generation to another – be
heritable
• Must lead to differential reproduction -
enable individuals with the trait to leave
more offspring than other members of the
population.

13. Adaptations or adaptive traits
• A heritable trait that
enables organisms to
better survive and
reproduce under a
given set of
environmental
conditions
• Selective pressure - a
factor in a
population’s
environment that
causes natural
selection to occur.
• Environmental
conditions do not
create favorable
characteristics

14. To summarize
• Genes mutate
• Individuals are selected
• Populations evolve
• Can also change populations by artificial
selection (see p. 100)
• Peppered moth - an example

15. Types of natural selection
• Directional natural
selection - conditions
shift so that
individuals at one end
of the normal range
become more common
than midrange forms -
“it pays to be
different”
• Most common during
periods of
environmental change
or when members of a
population migrate to
a new habitat with
different
environmental
conditions.

17. Second type:
• Stabilizing natural
selection - eliminates
individuals at both
ends of the genetic
spectrum and favors
average genetic make-
up
• “it pays to be average”
• Occurs when an
environment changes
little and members are
well adapted to that
environment.
• Individuals with
unusual alleles tend to
be eliminated

19. Third type:
• Diversifying natural
selection - disruptive
natural selection -
individuals at both
extremes of the
genetic spectrum are
favored and
individuals with
normal traits are
eliminated.
• “It doesn’t pay to be
normal”
• Population is split into
two groups
• Occurs when there is a
shift in food supply
selected against
average individuals

21. Coevolution
• Populations of two
different species
interact over a long
time and changes in
one gene pool lead to
changes in the gene
pool of another
species
• Owls become better at
hunting mice; certain
prey have traits that
allow them to escape
• Some of the predators
have better eyesight
and are more
successful hunters and
they pass this trait to
their offspring.

22. Ecological niche
• Way of life or role in the
ecosystem
• Involves everything that
affects survival and
reproduction
• Includes: range of
tolerance for chemical and
physical requirements
• Important because:
– Can prevent extinction
– Can help assess
environmental changes.
• Types of resources used -
food or nutrients
• How it interacts with
biotic and abiotic factors
• Role in the flow of energy
and matter cycling
• Represents adaptive traits
that organisms have
acquired through
evolution that allow for
better survival.

23. Fundamental niche
• The full potential range of physical,
chemical, and biological conditions and
resources an organism could theoretically
use if there was no competition with other
species.
– Niches however, often overlab

24. Realized niche
• In order for an organism to survive and
avoid competition for resources it will use
only part of its fundamental niche – this is
the realized niche.

25. Generalist species
• Occupy broad niches
• Can live many places
• Eat many types of food
• Tolerate a wide range of environmental
conditions
• Flies, cockroaches, mice, etc

26. Specialist species
• Have narrow niches
• Live in only one type of habitat
• Eat only one or a few types of food
• Tolerate only a narrow range of climactic and
environmental conditions
• More prone to extinction during changes in
environmental conditions
• Examples: tiger salamander, red-cockaded
woodpecker, spotted owls, giant panda

27. Limits to adaptation
• Changes in
environmental
conditions can lead to
adaptation only if the
traits are already
present in the gene
pool
• Because each
organism must do
many things
• Adaptations are
usually compromise
• Even if a beneficial
trait is present, the
population’s ability to
adapt is limited by its
reproductive capacity
• Adapt, migrate or die

28. Convergence or convergent
evolution
• Species with similar
niches tend to evolve
similar traits that
enable them to survive
and reproduce even
though they are in
different parts of the
world

29. macroevolution
• Evolution that takes
place above the level
of species and over
much longer periods
• Patterns include:
– Genetic persistence -
inheritance of DNA
molecule through all
subsequent lines of
descent
– Genetic divergence -
long term changes in
lineages of species
– Genetic losses - steady
loss (background
extinction) or abrupt,
catastrophic loss (mass
extinction) of lineages
– Example: the horse

30. How do new species evolve?
• Speciation - two
species arise from one
• Usually takes place in
two phases:
– Geographic isolation -
• Populations become
separated for long
periods of time
• Migration to new area
• Physical barrier such as
a road
• Earthquake
– Reproductive
isolation -
• Mutation & natural
selection act on isolated
populations - called
divergence - eventually
cannot interbreed
– Divergent evolution -
arises from speciation
– Usually takes tens of
thousands of years

31. Speciation

32. Extinction
• Can be caused by
large scale movement
of the continents
(continental drift)
• Gradual climate
change
• Rapid climate change -
volcanic eruption, etc.
• Extinction is the
ultimate fate of all
organisms
• Biologists estimate
that 99.9% of all
species that have ever
lived are now extinct.

33. Types of extinction
• Background extinction
- species disappear at a
low rate as local
conditions change
• Mass extinction -
abrupt rise in
extinction rates -
catastrophic, often
global-wipes out large
groups of species
• Generally believed to
be the result of climate
change.
• Five mass extinction s
- 20 - 40 million years
apart
– Last one took place
about 65 million years
ago - wiped out the
dinasaurs

34. Adaptive radiations
• Periods of recovery
• Numerous new species
evolve over several
million years to fill
niches vacated by
extinct species
• Explosion of
mammals after
dinosaurs became
extinct

35. Biodiversity =
• Speciation minus extinction
• Humans have become a major force in the
premature extinction of species.
• We may cause extinction of up to a quarter
of the earth’s current species
• On short time scale, new species cannot
form rapidly enough
• We are impacting the earth