Lesson 3:
Interactions among
Living Things
Grade 7 Science
Interactions in the Environment
Interaction among Living
Things
O Learning Goals:
O Explain how an ecosystem if limited in the number
of living things it can support.
O Success Criteria:
O I can explain how abiotic factors limit the number
of organisms in a given area.
O I can explain how predation and competition limit
the number of organisms in a given area.
O I can describe and give examples of mutualism.
Recall that a population is all the
members of a particular species
found in one area.
Populations can vary in size. They
can be large, such as an ant colony, or
small, such as a single pair of
breeding woodpeckers in a woodlot.
What determines the size of these
populations?
Abiotic Factors
O Abiotic factors limit the number
of organisms that can live in an
ecosystem. Let’s discuss some
examples of this:
Biotic Factors related to
Abiotic Factors
O How organisms interact within an
ecosystem also limits the
number of organisms in an
ecosystem.
O Two important biotic interactions
are competition and predation.
Competition: occurs when
more than one organism
tries to obtain the same
basic resources in the same
habitat
Competition is the struggle that happens when
organisms in the same habitat try to use the same
resources.
Can anyone think of an example???
Competition Examples:
1. plants that grow close together in one
area compete for the same water,
sunlight, and nutrients.
2. When farmers grow crops, they spray
pesticides on the crops to stop other
organisms from eating them. Farmers
are able to control, or even eliminate,
competing organisms.
Predation
O Predator: an organism that hunts other
living things for food
O Prey: an animal that is hunted by a predator
O Example: A wolf (predator) eating a moose
(prey) is an example of a predator-prey
relationship
O A moose eating grass is not an example of a
predator-prey relationship because the
moose does not need to hunt the grass
Predation
O The population of predators is affected by the population of
prey and vice versa. The number of predators can only
increase if there is enough food to eat. If a predator
population is increasing in size, the prey population will
decrease in size because more predators are eating prey.
O However, if the prey population gets too low, there is not
enough for the predators to eat. The predator population
decreases; some die from starvation and others may be too
weak to produce young.
Predation
O This video gives more examples of
predation. Notice the other factors that are
mentioned that are necessary for organisms
to live. Be ready to discuss some examples
from this video:
O Predators and Prey in an Ecosystem
Mutualism
O Mutualism: an interaction between
individuals of different species that
benefits both individuals
O Example: When a bee visits a flower. The bee
takes nectar from the flower for food, and picks
up pollen from the flower while doing so. The
pollen is that transferred to the next flower the
bee visits. This transfer of pollen allows plants to
reproduce. The nectar benefits the bee and the
transfer of pollen benefits the flower.
Interactions among Living
Things
O The following video illustrates the concepts
we have talked about in this lesson. Be
ready to discuss some examples after
watching the video:
O Competition, Predation and Symbiosis
(Mutualism)
O Competition and other Interactions (skip
first 1min)
Let’s play with some
simulations.
Gizmo time!