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Chapter 22
Populations and Communities
22-1: Living Things and the Environment
Ecosystem- all living and nonliving things that
interact in a particular area
Look at the picture below, and list all the living and
non-living things you see on the side of your notes:
Habitat- the place where an organism lives and that
provides the things an organism needs.
In other words: a habitat is SPECIFICALLY the
place in the ecosystem where an organism obtains
food, water, shelter, and other things it needs to live,
grow, and reproduce from its surroundings
Question: What is the ladybug’s habitat in the picture above?
Answer: The ferns that grow along side the pond.
• Organisms interact with both the living and the non-living
portions of the ecosystem.
• Ecosystems are divided into two main parts: Biotic Factors
and Abiotic Factors.
Biotic Factors: living parts of an ecosystem
Abiotic Factors: nonliving parts of ecosystem
that affects the living things in an ecosystem
Look at the example below. List the Biotic and
Abiotic factors on the side of your notes.
Biotic Factors: Don’t forget about the living things that may be
underground such as worms, fungi, and bacteria…..Q: Why are
these biotic factors important to the ecosystem?
A: These organisms keep the soil rich in nutrients as they break
down the remains of other living things.
Abiotic Factors:
1) Water- All living things require water to carry out processes.
2) Sunlight- necessary for photosynthesis
3) Oxygen- required for life processes: land- get it from air,
water- get it directly from the water
4) Temperature- determines what type of organisms can live
there. Some animals can alter their environments to
overcome temperature challenges.
5) Soil- influences what type of plants can grow there and what
type of animals can use the soil for a home.
Levels of Organization Review:
Organisms- build populations which build
communities which build ecosystems
Organism - one individual Example: _________
Population- all the members of a species in a particular
area. Example: ___________________________________
The area in which a population lives can be as small as
a blade of grass or as large as the whole planet.
However, scientists studying populations usually limit
it to a defined area.
Some populations do not stay in a contained area.
Community- different populations that live
together in an area.
Example:_______________________________________
_______________________________________________
To be considered a community, different
populations must live close enough to one another
to interact.
Ways populations interact within a community:
1- Using the same resources like food or shelter or
competing for them
2- Predator- prey relationships
3- Symbiotic relationships
Ecosystem- different communities living
together along with the non-living
factors. Example: ______________________
______________________________________
For the next pictures: guess which level it
is showing! Word bank:
•
•
•
•
Species
Population
Community
Ecosystem
What level of organization?
Community
What level of
organization?
Organism
10
What level of
Organization?
Ecosystem
11
What level of
Organization?
Population
12
Ecology- study of how living things interact with
one another and with their environment
Ecologists look at how the biotic and abiotic
factors in an ecosystem are related.
They also study how organisms react to changes
in their environment.
Sometimes reactions are fast- like sending out a
warning of a predator.
Sometimes the reactions are slower- like returning
to “normal” after a natural disaster.
Ecological Methods
1) Observing- What kind? How
many?
2) Experimenting- In artificial
environments or out in the
natural world.
3) Modeling- Over long periods
of time, mathematical
formulas based on data, form
predictions.
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Why would it be difficult at times
to study ecology?
-Very large-scale studies
-Over long periods of time
-Organisms change
-Organisms move
-Environments change
-Natural disasters occur
-Involves a lot of travel
-Diversity of life is endless!!!
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22-2: Studying Populations
Population Density- number of individuals in a specific area
Formula:
population density = number of individuals
unit area
Before we practice using this formula, remember that the unit
of area can vary greatly depending on what population we
are studying.
Using the metric system:
Q: What would be a good unit of area for studying whales?
A: Kilometers
Q: What would be a good unit of area for studying bacteria?
A: Centimeters or Millimeters
Practice Population Density Problems:
1)
If there are 25 butterflies in a 20 ft2 area,
what is the population density?
2) If there are 8 lions in a 2 mile2 area what
is the population density?
3) If there are 3,000 bacteria in a 4 inch2 area,
how many would be in a 12 x 12 area?
4) You have a garden that is
15 x 9 feet. In two a square foot area, you
count 4 dandelions, how many are there in the
whole garden?
Try on your Own!
5) There is a pond in the woods that is
approximately
45 ft. x 30 ft. In one square foot there is 250
unicellular algae. How many could there be
in the whole pond?
Determining Population Size
There are four ways of determining population size.
1. Direct Observation- count, one by one, all of its members
2. Indirect Observation –when organisms are small or hard
to find, observe their tracks or other signs rather than the
organisms themselves
3.Sampling- when a population is very large or spread over a
wide area, estimate based on reasonable assumptions
4. Mark-and-Recapture Studies- an estimating method in
which some animals are first captured, marked, and released.
Then another group of animals is captured and using a
mathematical formula, the scientists can estimate the total
population.
Changes in Population Size
Populations can change in size when new members
enter the population or when members leave the
population.
How can this happen?
1- Births
birth rate- number of births in a population in a
certain amount of time
2- Deaths
death rate- number of deaths in a population in
a certain amount of time
***The Population Statement:
a. if birth rate > death rate, population size increases
b. if death rate > birth rate, population size decreases
3- Immigration - moving into a population
4- Emigration- leaving a population
*can occur when part of a population gets
cut off from the rest of the population
Graphing Changes in Population
*in figure 8, vertical axis shows the numbers of
rabbits in the population, while the horizontal
axis shows time
Limiting Factors
limiting factor - is an environmental factor that prevents a
population from increasing
carrying capacity- largest population that an environment can
support (based on limiting factors)
There are three main limiting factors:
1- Food- if food is scarce, it becomes a limiting factor
2- Space- space is often a limiting factor for plants
because it can determine how much sunlight, water, and
other necessities the plant can obtain.
3-Weather- temperature and rainfall can limit population
growth and a single severe weather event can dramatically
change the size of a population by killing organisms
22-3: Interactions Among Living Things
Adapting to the Environment
Natural Selection Review (From Chapter 5)
1- Individuals in populations have different
characteristics
2- The individuals whose characteristics are better
suited for their environment will survive and produce
offspring.
3- Offspring that inherit the favored characteristic will
also survive to reproduce.
4- Over many generations individuals with that
characteristic will continue to reproduce.
5- Individuals without the characteristic will die off from
the population over time.
Adaptation- physical characteristics or behaviors that allow
organisms to live successfully in an environment.
Every organism has a variety of adaptations
that are suited to its specific living conditions.
Examples- a cactus can store water, a
woodpecker has a long beak to feed off of the
cactus without getting hurt.
Adaptations
create unique
roles
for organisms in
an ecosystem.
Niche- An organism’s particular role in an
ecosystem, or how it makes a living.
Think of it as an organism’s “job description.”
Comparison to a human:
If the ecosystem is the varsity baseball field,
what are some niches within that ecosystem?
__________________________________________
__________________________________________
__________________________________________
__________________________________________
Niche can include:
- Type of food it eats
- How it obtains food
- What eats it?
- When it reproduces
- How it reproduces
- Physical conditions needed to survive
- How it interacts with other organisms
There are three main ways organisms
interact with one another:
1) Competition 2) Predation 3) Symbiosis
NO TWO ORGANISMS CAN SHARE THE
SAME NICHE!!!
They can share habitat, food
requirements, and maybe one or two
other things, but never the same EXACT
niche.
Why? Because that would create direct
competition and one
species would win
(survive) and one
would lose (die off).
Example: Warblers
Competition- the struggle for an organism to
survive in a habitat with limited resources.
An ecosystem cannot satisfy the needs of all
living things in a particular habitat.
There is a limited amount of food, water, and
shelter. Q: So what survives?
A: The organisms with the best
adaptations to reduce competition.
The warblers all “specialize” to eat from a
particular area of a spruce tree, thus avoiding
competition.
Predation- Interaction in which one organism
hunts and kills another for food.
Predator- Organism that does the killing.
Prey- Organism that gets caught and killed.
Predator Adaptations
- Help them catch and kill pray
- Examples: cheetah’s speed, jellyfish’s
tentacles, wolf’s sharp teeth
Prey Adaptations
- Help them avoid being caught as prey
- Examples: Camouflage, protective covering,
mimicry, coloring
The Effect of Predation on Population Size
Size of population is a cycle of birthrate and
deathrate.
• If predators are effective at hunting prey,
the prey population is reduced.
• However, a decrease in prey can leave the
predators without enough food.
Read pg. 7082nd paragraph to
interpret graph.
Symbiosis- A close relationship between two
organisms in which at least one benefits.
There are three types of symbiosis:
1- Mutualism
2- Commensalism
3- Parasitism
Mutualism- A symbiotic relationship in
which both organisms benefit. (WIN-WIN)
Example- Bacteria and human (intestines)
Commensalism- A symbiotic relationship in which
one species benefits and the other is neither helped
nor harmed. (WIN-DRAW)
Example- A barnacle and a whale
Parasitism- A symbiotic relationship in which one
organism lives inside or on another and causes
harm. (WIN-LOSE)
Parasite- The organism that benefits
Host- The organism that the parasite lives in or onusually harmed.
Example- A flea and a dog