A presentation about biodiversity and evolution.

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