Grade 9 Academic Science – Unit 1 Sustainable Ecosystems
Abiotic and Biotic Factors
Section 2.7 – Pages 52-55
LIMITING FACTORS are factors that can determine which types of organisms AND how many of each
species are able to survive in a certain area or ecosystem.
 Limiting Factors can be either abiotic
(e.g., water, temperature, wind) or biotic
(e.g., types of plants available to eat,
types of animal predators in the area).
TOLERANCE RANGE is the range of abiotic
conditions within which a species can survive.
As the figure shows, some organisms cannot live
in conditions of extreme dry and extreme wet.
The Tolerance Range for most species lies in
between the dotted vertical lines. In this case, the zone with
the most species is the OPTIMUM RANGE
 Some species have very wide tolerance ranges, while
other species have narrow ranges. An example of a
species with a narrow tolerance range is a tube
worm. This species only lives in the ocean thermal
vents deep in the Pacific Ocean. To live, the tube
worm needs high pressure, high temperature and low
acidity.
 The LAW OF TOLERANCE states that the
distribution of a species will be limited by the species
range of tolerance for local environmental factors
ABIOTIC FACTORS are non-living factors that can limit an
organism’s ability to survive. Abiotic Factors include amount
and quality of light, air temperature, pH, wind speed, intensity
of sunlight, humidity, availability of oxygen, nutrient (i.e., food)
availability, etc. NOTE: Cycles such as the carbon cycle and
water cycle are Abiotic Factors. Also see Table 1 on Page 53 of your textbook.
Task
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Graph the data presented in Table A.
Do you think (1) a polar bear, (2) cactus and (3) squirrel could survive in these conditions.
Explain each of your answers referring to your graph.
Table A. Climatic Data
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Temperature
(OC)
-16.2
-12.3
-6.8
2.9
10.2
13.8
15.9
14.8
9.9
4.1
-6.1
-13.0
Precipitation
(mm)
34.9
25.1
22.7
19.4
36.6
69.0
67.0
55.5
39.6
24.4
28.7
30.3
BIOTIC LIMITING FACTORS often determine how “easily” a species can survive.
 Biotic Factors include competition, predation, decomposers and population density.
 In competition, organisms, species or populations compete with each other for limited resources
such as food, space, mates, and light.
 There are five Biotic Limiting Factors. See Table 2 (Page 54 in your textbook) to complete this
RELATIONSHIP chart AND with this information, complete the INTERACTIONS AMONG
ORGANISMS chart.
Table B. Key Relationship Types of Species Interactions
Relationship
Definition
Example
Competition
Predator – Prey
Mutualism
Commensalism
Parasitism
Table C. Interactions among Organisms
Type of Interaction
Competition between A and B
Effect on Organism A
Effect on Organism B
Harms
Harms
A predates on B
A is a parasite to B
Mutualism between A and B
Commensalism between A and B
CARRYING CAPACITY is the limit of the ecosystem. That is, it is the maximum population size of a
species that a given ecosystem can sustain indefinitely. Why?
 As a population grows, the demand for resources such as food, water, shelter and space
increases. Eventually, there are not enough resources for each individual. This causes crowding
or overconsumption of resources. As conditions worsen, the organisms become more
susceptible to predation and disease.
Carrying Capacity
Total Demand on Resources = Population X Average Demand per Individual
Do you think humans have a carrying capacity? Explain.
Homework
 Page 55, Questions 1-3, 6-8
AFRICAN SAVANNAH
An African savannah includes the following organisms. Examine each organism and determine its
relationship with the other organism of the savannah. For example, a hyena may be a COMPETITOR
with a lion.
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Hyena
Impala
Lion
Termite
Wildebeast
Zebra
Cheetah
Tapeworm
Ticks
Hare
Elephant
Wild Dog
Vulture
Rhino
Giraffe
Aardvark
Warthog
Mice
Mongoose
Antelope
Cattle egret
Liver flukes (Flatworms)
Army ants
Red-billed Hornbill
Grasshopper
Red-billed oxpecker