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 billion years
Chemical evolution came first
Biological evolution - about 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 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