Populations & Communities
Obj: 11B
Investigate and analyze how
organisms, populations, and
communities respond to
external factors.
What is an organism?
• An individual living thing, such as
a bacterium, protist, fungi, plant,
or animal.
What is a population?
• A group of one species of organisms
that live together in a certain area.
Examples:
• Humans living in the city of Houston
• Tree frogs living in a forest
What is a community?
• A group of populations of different
species that interact with one another.
Example:
• Populations of tree frogs, snakes, birds,
as well as other animals and plants all
living together on a tropical island
What is an ecosystem?
• Communities in the environment
• Includes abiotic (non-living) and
biotic (living) factors.
Example: the tropical island
How do organisms respond to
external factors?
• When a rabbit
senses that a
predator is
near…
It runs away or hides in a burrow
• When a skunk feels threatened…
It sprays its attacker with a foulsmelling liquid
• When an opossum is attacked…
It curls into a ball, and pretends to
be dead.
• Plants that grow as vines, such as
pumpkin and ivy, produce tendrils
that can wrap around surfaces
• Roots of
plants tend to
grow toward
wet soil, while
the leaves
grow toward
light
How do populations respond to
external factors?
• Predator & prey relationships
• Competition among predators
• Invasive species outcompete
natives
• Disease
Predation
Competition
Invasive species
• Asian carp were
introduced to
Michigan lakes to
control algae.
• Now introduced
species
outcompeting
native fish for
food.
Pythons in the Everglades in Florida
Disease
How do communities respond to
external factors?
What happens to
the snake
population when
the toad
population dies
out due to
disease?
Volcano Explosion
Oil Spills
The Role Microorganisms
11C: Summarize the role of
microorganisms in both maintaining
and disrupting the health of both
organisms and ecosystems.
What is a microorganism?
• Any organism that cannot be seen
without the aid of a magnifying glass
or microscope
• Examples – bacteria, protists, fungi
• Found in almost every habitat on Earth
How can microorganisms maintain
the health of other organisms?
Mutualistic Relationships
• Microorganism gains benefits such as
a warm environment to inhabit and
gain nutrients
• Animal or plant may gain benefits
such as protection from other
microorganisms or a supply of
enzymes they need but cannot
produce
• Example – bacteria living in guts of
termites & cows to produce enzymes
to digest cellulose
• Example - Fungi & plants form
relationship called mycorrhizae.
• The Fungi collect water & minerals
and deliver them to plant roots
• The Plants provide the fungi with
nutrients made through
photosynthesis.
• Example – Plants called legumes
contain bacteria of the genus
Rhizobium in structures on their
roots called nodes.
• The Rhizobium fixes atmospheric
nitrogen so that is is available for
plants to use.
How can microorganisms disrupt
the health of organisms?
Parasitic Relationships
• Some microorganisms causes diseases
in a host. These microorganisms are
called pathogens.
• Pathogens cause a disease by killing
the host cells, releasing toxins, or
interfering with the processes within
the host’s body.
Lyme Disease
• Caused by at least three species of bacteria
belonging to the genus Borrelia.
Tetanus
• Caused by the bacteria Clostridium tetani.
Strep Throat
• Caused by the bacteria Streptococcus
pyogenes.
How do microorganisms maintain
the health of ecosystems?
Mutualistic Relationships
• Microorganisms recycle nutrients.
Decomposers break down organic
matter of dead plants & animals.
• Some bacteria living on the ocean floor
feed on oil that seeps from the ground.
How do microorganisms disrupt
the health of ecosystems?
• Pathogens (microorganisms that
cause disease) can kill off large
numbers of a plant or animal species
that is important to the health of the
ecosystem.
Example
• In oak forests, many animals depend
on the acorns that fall each autumn
for food.
• What would happen if a pathogen
infected the oak trees and prevented
them from producing acorns?
Oak Wilt
Caused by the fungus
Ceratocystis fagacearum.
• Algal blooms in aquatic ecosystems such as
oceans can block sunlight and cause death of
plants along with organisms that eat the
plants.
• Bacteria populations rise because of an
increase in food supply of dead organic
matter.
• Oxygen levels drop because of the bacteria
population increase. Fish and other organisms
then die. These areas are called dead zones.