Download Limiting Factors

Lets think about it…
Appendix 1.1. – Environmental factors and population
size
Activity #1: Animal Crackers
 Definitions:
 Population: the total number of
animals/plants/things of one type in a
particular area

Example: All the geese in Birds Hill Provincial
Park. All of the water beetles in a pond. All
the desks in this room.
What is a Limiting Factor?
 Limiting Factors are…
(two similar definitions)
 conditions of the
environment that
limit the growth of a
species.
 biotic and abiotic
factors that prevent the
continuous growth of a
population.
What is a Limiting Factor?
 Populations would continue to increase if
they had all of the resources they require in
unlimited amounts, but there are always
factors that limit their increase.
 Limiting factors control
population growth.
Let’s list some Limiting Factors!
Can a population continue to
grow at this rate forever?
 The answer, of course, is no.
 The environment becomes limiting.
 Resources such as food and water become scarcer
and the rate of population increase begins to slow.
 The graph below illustrates a population growth
curve of this nature.
Think back to the housefly problem. Over the
months the number of flies increased from 900
flies in January. 400 000 flies by late February.
180 000 000 flies in March. The number of flies
increased slowly at first and then very rapidly.
However; having a few hundred million flies in
your home in March is highly unlikely.
Why is this so?
What is Carrying Capacity?
 Because of these limiting factors, each
ecosystem has a finite capacity for growth
connected to its carrying capacity.
What is Carrying Capacity?
 Carrying capacity is
the number of
individuals of a species
that an ecosystem can
support.
Exponential growth phase –
population grows rapidly
Lag phase – population
is slowly increasing
Steady state phase –
population has reached its
carrying capacity
Decline phase – population
decreases due to:
There are four main factors that affect the carrying
capacity of an ecosystem.
1. Materials and Energy: All populations are affected by
the amount of usable energy from the Sun (which could
be in the form of animals or plants) as well as water and
carbon supply.
1. Food Chains: Populations at one trophic level are
affected by the number in all levels above and below it.
 i.e: Populations are affected by their food supply. (The
animals/plants below it in a food web.
 Populations are also limited by their predators. (The animals
above them on a food web.)
3. Competition: The demand for resources such as food,
water, mates, and space. This also affects the carrying
capacity of an ecosystem.
4. Density: Depending on an animal’s need for space this
determines their population density. (Population
density is how many animals can live in an area at a
time.)
 Competition:
The demand for resources such as
food, water, mates, and space. This also affects the
carrying capacity of an ecosystem.
 There are two types of competition:
 intraspecific competition: competition among the same
species

Example: The competition between two bears in the same territory.
 interspecific competition: competition among
different species

Example: The competition between a bear and a wolf in
the same territory.
 There are two types of factors that affect population
density:
 density-dependent factors: These are factors that
increase in importance as population grows. These things
are influenced by an increase or a decrease in population.
 Examples: food supply, disease
Water
Disease
Food
Shelter/
Space
 density-independent factors: These are factors that
affect populations regardless of their size to begin with.
These factors will take place regardless of an increase or
decrease in population.
 Examples: forest fires, predators, natural disasters, floods,
droughts
*Factors that limit the size of a population but DO NOT
depend upon the size of the population.*
Natural Disasters
Hunting
Logging
On Graphs
If you draw a line through the middle of the
population fluctuations, that line represents the
carrying capacity of that environment for that species.
Go back to Population Growth Curve 2 and draw a line
that represents the carrying capacity.
Population Growth Curve: Carrying Capacity
Carrying
Capacity
Limiting Factors
 In nature, populations of organisms rarely grow
uncontrolled. Each ecosystem has a carrying
capacity (or number or organisms it can
sustain/support).
 Remember, limiting factors are biotic and abiotic
factors that prevent the continuous growth of a
population.
 Because of limiting factors, the number of
organisms in a population is often well below
carrying capacity.
Populations
The rate at which a population grows can be calculated.
Four factors that are part of the growth rate equation are
births, deaths, immigration, and emmigration.
Rate of Population Growth Equation
Formula
Rate = (# of Births + # of Immigrants) – (# of Deaths + # of Emmigrants)
Extremely fast growth in a population is called a Population
Explosion.
Reasons for a population explosion are…
1.
2.
3.
New species introduced to an environment with few predators.
Plentiful food supply.
Abundant space.
An Alien Species is the term for the introduction of a
foreign species to a new environment.
Two examples in the Great Lakes were the
introduction of Zebra Mussels and Asian Carp.
 When a greater number of species leave a population
compared to the number of species entering the
population, this is called population extinction.
Assignment
 Limiting factors
 Carrying capacity
 Population terms
 Watch March of the Penguins
 Complete movie questions