Download population ecology - Ms Williams

POPULATION ECOLOGY
What is a population? A group of organism of the
same species living in an area
List 3 different populations that would be found in this
ecosystem.
1. ____Fox____________
2. ______hawk___________
3. ________squirrel________
Key Concepts:

Population DENSITY is the _number__ of individuals
in a population within a given area.

Population GROWTH is the __increase____ in the size
of a population over time.

CARRYING CAPACITY is the __maximum__ number
of individuals that an environment can support. (=
k)

There are certain factors that can control
population density, growth, and carrying capacity.
These are called LIMITING FACTORS.
How do populations grow? There are 2 general trends:
EXPONENTIAL GROWTH
LOGISTIC GROWTH
Graph:
Graph shape:
Description:
__J_ - shape curve
_S_ - shape curve
means that as a population gets
___larger__, it also grows faster.
shows that population growth stabilizes
Examples:
Bacteria, humans,
Trees, animals,
Limiting Resources?
no
Food, water, shelter,

When populations are under the carrying capacity of an environment, births exceed deaths until the
capacity is reached. In other words, there are more babies being ______________ than there are organisms
_____________________.
Logistic Growth: What is happening at…
1) Initial growth
2) exponential growth
3) carrying capacity
Check for Understanding
1. What type of graph (growth curve) is this? logistic
Check-for-Understanding:
2. What is the carrying capacity of the deer population ?
80
3. Explain why there might be a sudden decrease in the
deer population once their numbers hit about 95. The
ecosystem could not support that many individuals, so
‘some deer died off
What kinds of things can affect whether a population exhibits exponential or logistic
growth?
Density – Dependent
Limiting Factors
Description:
have negative effects as the population increases
(Think about it: As the population grows larger and larger,
disease is more easily spread, space becomes limited,
competition increases, and food becomes more difficult to
obtain. Hence, these density-dependent factors are affected
by the size (or density) of the populatin).
Examples:
Density-Independent
Limiting Factors
affect every populations, regardless of the
population size.
Food, water, shelter, disease
Natural disasters, hurricanes, forest fires, harsh
winter, human intervention
* What is the difference between density-dependent factors and density independent factors?
____________________________________________________________________________________________________________
____________________________________________________________________________________________________________
How do limiting factors influence carrying capacity?
Limiting Factor (density-dependent?
density-independent?)
Food availability (_density
dependent)
Example
In a pond ecosystem, the level of algae determines the carrying
capacity of a type of fish called carp. One summer the algae didn’t
bloom as much because of a lack of sunlight. What would likely
Competition (density dependent)
Harsh winter density independent
Disease density dependent
happen to the carrying capacity of the carp? decrease_ Why? no
food available
Two species of birds live in the same woodland area. They both
depend on lady bugs as their main source of food. One bird species is
more effective at capturing the insects. How will the carrying capacity
of this successful bird population compare to that of the other species?
Population will increase, due to successful gathering of food. Other
population will decrease, cannot compete successfully for food.
One winter a huge blizzard wiped out a northeastern forest population
of white rabbits. How would the carrying capacity of the wolf
population (that preys upon those rabbits) be affected? The wolf
population would decrease to do a decrease in their food supply
In the winter it is well known that students are more likely to become
infected with the influenza virus. Explain why this is so. Students are in
close contact with each other and stay inside more, making it easier
for the disease to spread
Biotic Relationships within Ecosystems
#1 Predator Pray Relationships
1. In year 15 the rabbit population began to
increase. How did the fox population
respond? _The wolf population eventually
increased_
2. What happens to the rabbit population
then just after year 20? _it decreased
rapidly Why?
__________________________________
________________________________________
3. Why does the fox population never get as
high or higher than the rabbit population?
If there are more predators than prey, then
both populations will eventually die out
4. Draw 2 new lines on the graph to predict
how both populations will look by year 50.
#2 Symbiotic Relationships
Symbiotic Relationships
Relationships where 2 different species
have a close relationship with each
other
Mutualism
Both species benefit
Commensalism
One benefits, the other is not
affected
Parasitism
One species benefits, the
other is harmed