1. The Organization of Life
Chapter 4
Ms. Cuthrell
Ecology
2nd Period

2. Evolution by Natural Selection
1859, Charles Darwin proposed an answer to the question, “how do organisms become so well suited for their environment?”
The answer he proposed is Evolution by Natural Selection

3. Evolution by Natural Selection
Darwin noticed that in a population (same species living in same place) the organisms are slightly different in:
Form- how the body is shaped/colored
Small beaks vs. Large beaks
Function- what the body does
Eating small seeds vs. Eating large seeds
Behavior- what the organism does
Ignoring humans vs. Running away

4. Evolution by Natural Selection
“Survival of the Fittest”
In a certain environment, certain traits will help an organism survive
These organisms will have more offspring
The next generation will have more traits that are like those organisms
Over time the population will evolve, so that the traits that help survival will be found in more organisms

5. Evolution by Natural Selection
Darwin’s theory can be summarized in 5 steps:
Organisms produce more offspring than can survive
The environment is hostile and has limited resources
Organisms differ in the traits they have
Some traits provide an advantage
Each generation will have more organisms with advantageous traits
The traits that helps an organism survive are known as adaptations

6. Evolution by Natural Selection

7. Evolution by Natural Selection
Sometimes different organisms evolve to help each other out
This is called coevolution
Insects get food by eating the nectar inside flowers
The have long straws that help them do this
The flowers give off pollen, which attached to the insect
When the insect go to another flower it pollinates the new flower

8. Evolution by Artificial Selection
Since the agricultural revolution we have been domesticating animals and crops
We breed animals so they have the traits we need them to have
Horses = speed/strength
cows = quality of meat
Dogs = beauty
Crops are breed to grow faster, bigger, be disease resistance, different colors, …

9. Evolution by Artificial Selection
This type of selective breeding that is controlled by humans is called
Artificial Selection.
The Chihuahua is a
descendent of
the grey wolf.

10. Evolution of Resistance
In our quest to control nature we spray pesticides to kill insects
Unfortunately we have used pesticides, so much that insects have become resistant
An organism can tolerate a chemical that is designed to kill it

11. Evolution of Resistance

12. Genetics
Around the same time as Darwin, an Austrian monk, Mendel, was studying pea plants
He was trying to understand how different traits are passed from parents to children
Mendel breed different types of pea plants together and observed the flower color and type of peas

13. Genetics Mendel came up with 3 conclusions:
There are different forms of the units that control traits (flower color, pea type, eye color, …)
For each trait there are 2 units, 1 from each parent
If the units are different, then 1 of them is dominant and the other is recessive
We have found out since then that the “unit” is a gene

14. Genetics
In order to keep a population healthy, there must be genetic variation
Members of a population with different traits
(eye color, thick/thin fur, small/large beaks, …)
This variation comes in 2 major ways:
Mutation
Genetic Recombination

15. Genetics- Mutation
A change in the gene of an organism that can be passed to its offspring is a mutation
Mutations that effect a single gene can do cause a range of damages
These are typically not even noticed
If they are noticeable then they are usually severe and cause serious damage
Mutations that effect multiple genes usually result in the death of the organism

16. Genetics- Genetic Recombination
Genetic Recombination occurs when organisms reproduce sexually
Genes from 2 organisms combine to create an offspring
There are approximately 8 million unique genetic combinations in humans
If an organism reproduces asexually, then the genetics are exactly the same as the parent
Without mutations the population would not evolve

17. Genetics- Evolution
If you look at evolution using genetics, then evolution can be defined as a change in gene frequency in a population
Which genes are the most/least common
Remember: Individuals do not evolve, populations evolve.
The beauty of Natural Selection is in its simplicity
It does not require any certain direction or end result
It is only guided by random mutations in DNA

18. Ecosystems
Ecosystem
All organisms living in an area together with their physical environment
All plants, animals, rocks, water, and everything else
All living and nonliving things!
All ecosystems are connected!

19. Ecosystems All ecosystems need 5 things to survive: Energy
Mineral Nutrients
Water
Oxygen
Living Organisms

20. Ecosystems Biotic Factors Abiotic Factors
Organisms (the living things) and stuff that came from organisms
Plants, animals, leaves, bodily waste
Abiotic Factors
The nonliving part of the ecosystem
Air, water, sand, rocks, light, temperature

21. Ecosystems Organism Species An individual living thing
You, me, that bug living on your eyelashes!
Species
Group of organisms that are closely related and can mate to produce fertile offspring

22. Ecosystems Population
All members of the same species that live in the same place at the same time.
Members of 1 population will usually breed with each other rather than with other populations
You wouldn’t fly to another country just to find someone to marry

23. Ecosystems Community A Pond You can belong to more than one community
Various species that live in the same place and interact with each other
A Pond
Plants, fish, insects, animals that live around the pond
You can belong to more than one community
Birds that migrate during the seasons

24. Ecosystems

25. Ecosystems Habitat The place where an organism lives Cactus = desert
Waterlily = pond
Salamander = damp forest floor