Download Lesson 5 - Abiotic and Biotic Factors

Grade 9 Applied Science – Unit 4
Biotic and Abiotic Factors
Why do zebras only live on the grasslands of Africa? Why do Black Bears in North America live
in temperate forests? Why do only find cacti in deserts? It is because of factors that restrict the
size of a population called LIMITING FACTORS. The factors are BIOTIC and ABIOTIC
FACTORS.
• BIOTIC FACTORS are living things. It is the way living things interact or relate to one
another. Plants, animals and bacteria are all biotic factors.
• ABIOTIC FACTORS are non-living physical and chemical components of an ecosystem (e.g.,
temperature, wind, snow).
ABIOTIC FACTORS
Each species can survive
within a range of the
abiotic factors. This is
called TOLERANCE
RANGE. The graph
shows tolerance. For
example, we would find
large numbers of zebras
on the Africa grasslands
(Area of greatest
abundance). If we move
away from the grassland
to desert or tropical rainforest, population numbers decrease until there are zero zebras. Why? It
may be that zebras cannot live in extremely hot temperatures (i.e., desert) or very wet conditions
(i.e., rainforest). NOTE: Each species has its own Tolerance Range. That is, some species live
in very specific conditions (i.e., small or narrow Tolerance Range) while other species can live in
a wide variety of conditions (i.e., large or wide Tolerance Range).
For the following table, identify why you think these factors are Abiotic Factors.
Ecosystem
Abiotic Factor
Your Reason
Aquatic
Light availability
Acidity of the water
Water Temperature
Salinity (salt levels
in the water)
Nutrient availability
BIOTIC FACTORS
Abiotic Factors may influence WHERE organisms live, while Biotic Factors can determine HOW
successful organisms can survive. For example, wolves hunt…and thus survive…more
effectively in packs. This relationship is a Biotic Factor.
Biotic Factors are the interactions between individuals
Complete the following table with an EXAMPLE supporting the relationships of Biotic Factors
Relationship
Definition
Description
Your Example
Competition
Predation
Mutualism
Parasitism
Commensalism
Two individuals fighting for the
same resource
One individual kills and eats
another organism. One benefits
while the other is harmed
Two individuals that live together
and both benefit from the
relationship
-+++
One organism lives and feeds
on a HOST organism. The
parasite benefits but the host is
harmed
+-
One individual benefits from the
relationship while the other
organism neither benefits or is
harmed
+O
As the size of a population grows, the demand for resources (e.g., food, space, water, shelter)
also increases. Eventually, there will not be enough resources to share so all individuals survive.
This is called CARRYING CAPACITY. It is the maximum population size of a particular species
that an ecosystem can sustain indefinitely.
PRACTICE QUESTIONS
1. List three Abiotic Factors that are important to a land (terrestrial) ecosystem. Provide
your explanation for each factor identified.
2. Provide an example of parasitism and mutualism
3. Are Abiotic Factors less important than Biotic Factors? Explain your idea.
4. Canada’s Arctic is extremely cold. List three adaptations on the body of a polar bear that
allow it to thrive in the Arctic.