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Populations and Communities
Table of Contents
Living Things and the Environment
Studying Populations
Interactions Among Living Things
Changes in Communities
Populations and Communities
Living Things and The Environment
All living things must interact with their
surroundings.
Organism —a complete and whole living thing
Habitat —a place where an organism lives. It
provides food, water, shelter and a place to
reproduce. Ex: a woodpecker’s habitat is
the trees in a forest.
Niche —the role of an organism in its
community. How it makes a living. Ex: a
woodpecker’s niche is catching and eating
insects.
Populations and Communities
Biotic and Abiotic Factors
Biotic Factors —all living parts of an organism’s
habitat.
Abiotic Factors —all nonliving parts of an
organism’s habitat. (water, sunlight,
oxygen, temperature, soil)
Populations and Communities
Levels of Organization
The living things in an environment must be organized into
larger and larger groups within their environment.
Species —a group of organisms that are physically
similar and can mate with each other and
produce offspring that can also mate and
reproduce.
Populations —all the members of one species in a
particular area.
Community –- all the different populations that live
together and interact with each other in a
particular area.
Populations and Communities
Levels of Organization
Ecosystem —the community of organisms that
live in a particular area, along with their
nonliving surroundings. Ex: pond, garden, forest
Biosphere —the entire region of the world where
living things are found.
Ecology —the study of how living things interact
with each other and with their environment
Populations and Communities Living Things
and the Environment
Levels of Organization
The smallest level of organization is a single organism,
which belongs to a population that includes other members
of its species.
Populations and Communities Living Things
and the Environment
Levels of Organization
The population belongs to a community of different
species.
Populations and Communities Living Things
and the Environment
Levels of Organization
The community and abiotic factors together form an
ecosystem.
Populations and Communities
Four Characteristics of a Self-sustaining Ecosystem
A self-sustaining ecosystem has four characteristics:
1. A constant source of energy (usually the sun)
2. Transfer of energy into organic compounds
(usually through photosynthesis)
3. Interactions between biotic factors
(predator/prey, mutualism, commensalism)
4. Cycling of materials (water cycle, nitrogen cycle,
oxygen/carbon dioxide cycle, nutrient cycle)
Populations and Communities
Studying Population Size
Four methods of determining population size:
1. Direct Observation —count all members of a
population.
2. Indirect Observation —observe and count signs of a
population. Ex: count nests or dens observed
3. Sampling —make an estimate of the population by
counting the number of organisms in a small area
(a sample), and then multiplying to find the number
in a larger area. Estimate —an approximation of a
number.
4. Mark-and-Recapture Studies —capture, mark, and
release organisms several times to calculate their
population number.
Populations and Communities
Changes in Population Size
Populations can change in size when members either leave
or join the population. Population size can change by births,
deaths, immigration or emigration.
Birth rate —number of births in a population in a
certain amount of time.
Death rate —number of deaths in a population in
a certain amount of time.
Birth rate > Death rate = population increase
Death rate > Birth rate = population decrease
Immigration —organisms move into a population
Emigration —organisms move out of a population
Populations and Communities
Population Density
Population Density —the number of individuals in a
specific area.
Population Density = Number of individuals
Unit area
Populations and Communities Studying
Populations
Changes in Population Density
In many situations, it is helpful to know the population
density–the number of individuals in a specific area.
Population density =
Populations and Communities
Limiting Factors
Limiting Factor —an environmental factor that causes
a population to decrease. They include:
food, water, space, and weather conditions
Limiting Factors help determine the carrying capacity of an
environment.
Carrying Capacity —the largest population that an
area can support .
Populations and Communities Studying
Populations
Changes in Population Size
Populations can change in
size when new members
join the population or when
members leave the
population.
Populations and Communities Studying
Populations
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a question for each
heading. As you read, write the answers to your questions.
Question
Answer
How do you determine
population size?
Some methods of determining population
size are direct observation, indirect
observation, sampling, and mark-andrecapture studies.
What causes populations to
change in size?
Some factors include birth, death,
immigration, and emigration.
What are limiting factors?
These are factors that can limit population
growth if they are unfavorable for the
organisms in the population. Food and
water, space, and weather conditions can
be limiting factors.
Populations and Communities
Adapting to the Environment
Each organism in a community has unique characteristics that
allow them to interact with each other and to survive.
Adaptations —the behaviors and physical characteristics
that allow organisms to live successfully in their
environment.
Natural Selection —individuals with the best adaptations
will survive to pass on these traits to their offspring.
These better characteristics will therefore become
more common in the population.
Populations and Communities Interactions Among
Living Things
Adapting to the Environment
Every organism has a variety of
adaptations that are suited to its specific
living conditions.
Populations and Communities
Interactions Among Living Things
There are three major types of interactions among
organisms: Competition, Predation, and Symbiosis
1. Competition —the struggle for organisms to
survive as they attempt to use the same
limited resources.
Animals compete for food, water,
shelter, territory and mates
Plants compete for sunlight,
water and growing space
Populations and Communities
2. Predation —one organism kills another for food.
Predator —does the killing Prey —is killed
-It helps control overpopulation of non-predatory
species.
-It helps weed out diseased or less-fit members
of a non-predatory species.
-Populations of predators and their prey rise and
fall in related cycles.
Populations and Communities Interactions Among
Living Things
Predator - Prey Interactions
On Isle Royale, an island in
Lake Superior, the populations
of wolves (the predator) and
moose (the prey) rise and fall in
cycles. Use the graph to answer
the questions.
Populations and Communities Interactions Among
Living Things
Predator - Prey Interactions
Reading Graphs:
What variable is plotted on
the x-axis? What two
variables are plotted on the
y-axis?
Year; numbers of wolves
and moose
Populations and Communities Interactions Among
Living Things
Predator - Prey Interactions
Interpreting Data:
How did the moose population
change between 1965 and
1972? What happened to the
wolf population from 1973
through 1976?
The moose population
increased and then
decreased; the wolf population
increased.
Populations and Communities Interactions Among
Living Things
Predator - Prey Interactions
Inferring:
How might the change in the
moose population have led to
the change in the wolf
population?
As the moose population
increased, more food was
available to the wolf
population and it increased.
Populations and Communities Interactions Among
Living Things
Predator - Prey Interactions
Drawing Conclusions:
What is one likely cause of the
dip in the moose population
between 1974 and 1981?
The wolf population increased.
Populations and Communities Interactions Among
Living Things
Predator - Prey Interactions
Predicting:
How might a disease in the
wolf population one year affect
the moose population the next
year?
Disease would cause a
decrease in the wolf
population, so fewer moose
would be eaten and the
population could increase.
Populations and Communities
Interactions Among Living Things
3. Symbiosis —a close relationship between two species
that benefits at least one of the species. Three types:
-Mutualism —both species benefit
Example—bees visit
flowers: bees get nectar
and flowers get pollinated.
Example—lichens: a
mutual relationship
between algae and
fungi: algae makes
food for the fungi and
the fungi makes living
conditions better for
the algae.
Populations and Communities
-Commensalism —one species benefits and the
other is neither helped nor harmed.
Example: barnacles attached to
gray whales: barnacles get a free
ride to find food and the whale is
unaffected. Gray whales can be
identified by their barnacle patches.
Some may carry as much as 400 lbs of
barnacles and whale lice.
Example: orchid growing on a tree:
orchid gets a place to grow and the
tree is unaffected
Populations and Communities
-Parasitism —one species benefits and the other
is harmed.
-Parasite —organism that benefits
-Host —organism that the parasite lives in or on and is
harmed.
1. Hookworm
2. Tapeworm
3. Tapeworm
eggs
4. Roundworm
5. Pin worm
Populations and Communities Interactions Among
Living Things
Using Prior Knowledge
Before you read, look at the section headings and visuals to
see what this section is about. Then write what you know
about how living things interact in a graphic organizer like the
one below. As you read, continue to write what you learn.
1.
1.
2.
3.
4.
What You Know
Organisms interact in different ways.
What You Learned
Organisms are adapted to their environments.
Organisms have niches, which are their roles in their habitats.
Organisms compete for resources. Some organisms eat
others, and this affects the size of populations.
Some organisms live together in symbiotic relationships, of
which there is mutualism (both benefit), commensalism (one
benefits, the other is not helped or harmed), and parasitism
(one benefits, the other is harmed).
Populations and Communities
Changes in Communities
Communities change constantly---sometimes suddenly;
sometimes slowly.
Succession —the series of predictable changes
that occur in a community over time. Two types:
1. Primary Succession —the series of changes that
occur in an area where no soil or organisms
exist. Example: Following a volcanic eruption.
Pioneer species —first species to populate such
an area. Examples: mosses and lichens
Populations and Communities Changes in
Communities
Primary Succession
Primary succession is the
series of changes that occur in
an area where no soil or
organisms exist.
Populations and Communities
Changes in Communities
2. Secondary Succession —the series of changes that
occur in an area where the ecosystem has been
disturbed, but where soil and organisms still exist.
Examples: following fires, hurricanes, tornados,
farming, logging or mining.
Populations and Communities Changes in
Communities
Secondary Succession
Secondary succession is the series of changes that occur in
an area where the ecosystem has been disturbed, but where
soil and organisms still exist.
Populations and Communities Changes in
Communities
Comparing and Contrasting
As you read, compare and contrast carbohydrates, proteins,
and lipids in a table like the one below.
Factors in
Succession
Possible cause
Type of area
Existing ecosystem?
Primary
Succession
Secondary
Succession
Volcanic eruption
Fire
No soil or organisms
exist.
Soil and organisms exist.
No
Yes
Populations and Communities
Graphic Organizer
Main Idea
There are four main ways to determine the size of a population.
Detail
Detail
Detail
Detail
Direct
observation
Indirect
observation
Sampling
Mark-andrecapture
studies