Ecology - Lamont High
Ecology - Lamont High
Study of Ecosystems
Abiotic & Biotic factors interacting
Biotic Factors include populations & communities
•Groups of pops
Same species: Same place: Same time!
Can you explain the difference between
a population and a community?
The definition for a population?
The definition for a community?
Biotic and Abiotic Factors?
Abiotic factors are
components of an
Biotic factors are
components of an
Can you tell me…
The difference between abiotic and biotic
factors in an ecosystem?
An example of an abiotic factor?
An example of a biotic factor?
Why is the picture in the previous slide an example
of a community and not an example of a
Variables we will consider:
Population Growth Rate and Patterns
area where animal has been seen
Fire Ant Range
Geographic range can change over time
due to abiotic factors.
Range Changes in Moose Populations
How has the geographic range of moose
changed since the 1870’s??
area where the population lives
where environmental conditions are best
How does an organism’s geographic range
differ from its habitat?
Role of the species in the community
Includes ALL biotic and abiotic factors a
species needs to survive
Each group has a different role to
Populations co-exist only if each group occupies a different niche
Explain the meaning of the term ecological niche.
Determined largely by habitat preference
Divided into three patterns:
1. Clumped - individuals grouped in patches due to
certain environmental factors (e.x. trees clump on south
slopes of river valleys b/c less direct sunlight and
- not very common
- biotic and abiotic factors have little effect
competition among individuals for resources
results in regular spacing
What is the difference between clumped, random
and uniform population distribution?
What factors are responsible for creating clumped,
random and uniform population distributions?
Number of organisms of same type in
same place, at same time
There are 2000 students at Centre High
during the 2004/5 school year.
Can be determined by exact count or
Describes number of organisms in a defined
eg. Snow geese at Beaver Hills =
# of geese per hectare
Density (D) calculated by dividing total
number (N) by amount of space occupied (S)
by the population
What is the difference between population size and
If 200 lemmings are living in a 25 hectare (ha)
area of tundra, what is the population density
of this area?
Use the formula D = N/S
After finding the population density, we
can find the rate of change over time
Change in number
Rate of growth
Change in time
Density Change example
In 1993, the mouse population in my
backyard was 50 mice/acre. After three
years, various control measures had been in
place, and the population dropped to 10
mice/acre. Calculate the rate of density
When arriving at their summer cabin, the Smiths
discovered 10,000 cockroaches roaming throughout
their 1000 m2 cabin. After 1 week, the exterminators
were able to control the situation and reduced the
cockroach population to 10 per 1000 m2. Calculate the
rate of density change.
Determined by four
as per capita
Using this table, calculate CGR for
Puffins are small marine birds
found off the coast of Atlantic
Canada. Calculate the population
growth rate of a puffin colony
based on the following population
Original population = 200 000
Natality = 15 000
Mortality = 10 000
Immigration = 175 000
Emigration = 160 000
Calculate the population density of shrews
per m2, if an average of 7.8 shrews are
found in an area 14 m wide by 20 m.
Calculate the per capita growth rate of a mouse
population if the original population size is 34 and
over a period of a week, 5 die, 8 are born, 12
immigrate into and 7 emigrate out of the area.
Present in mature ecosystems
Characterized by long term balance
Pops remain relatively stable over time
Great biodiversity = stability
Can be compared with homeostasis
Define dynamic equilibrium.
2 population types:
1. Open populations:
immigration & emigration occurs
2. Closed populations:
Density changes are result of natality
and mortality only
No immigration or emigration
eg. Game preserves
What is the difference between open and
Graph showing changes in a population over
X = time (independent or manipulated
Y = density or # of organisms (dependent or
Exponential Pop Growth
Growth Curve for Closed
1. Lag phase…slow…not enough
2. Growth phase….exponential increase
3. Stationary phase….natality= mortality
4. Death phase…decline
Not always present
Bacterial Growth Curve
4 distinct phases
Draw a growth curve for a closed population.
Label and define the four stages of this curve.
Growth Curve for Open Systems
When a limiting factor is introduced to a
population, curve results in an “S” shape
As organisms respond to increased nutrients,
Typical of an organism placed in a new environment
Equilibrium is established again and curve levels off
New carrying capacity (max. # of individuals
environment can support)
Define carrying capacity.
When does a population growth curve of an
open system show an “S shape”?
Population Growth Curves
Click on the link above
Read the instructions and hit the “run applet” button
Set the carrying capacity to 1000
Set the birth rate to 1.5
View the graph and draw this in your notes
Have you simulated an open or a closed population?
Change the parameters and try it again!
Human Population Growth
How could you describe the population growth
of humans in the past 500 years?
Hint: one word that begins with an ‘e’
Population Explosion & Crashes
Describe the bottleneck effect.
Boom and Bust Cycles
What trends do you see in the population curve
for Soay Sheep that give its characteristic
shape of “boom and bust”?
Wide base…fast growth
What information is given in a population
What shape would a histogram look like if it
were representing an declining population? A
stabilized population? A young population?
What are these graphs showing?
1. Which country demonstrates
a very high reproductive
2. Which country represents a
Show Age Structure
What do each of the histograms on slides 63 to
64 tell you?
What trends do you see in the population
curves on slides 63 to 64?
Max. # of offspring produced in ideal
Regulated by four factors:
offspring - max #/birth
survival capacity – chance that offspring
will reach reproductive age
procreation - # times/year organism
maturity - age when reproduction begins
All factors that limit pop.
Can be biotic or abiotic
Food, water, space, disease, predation, natural
disasters, availability of mates, etc
Define biotic potential and environmental
resistance. Give an example for environmental
Affect population size!
flood, fire, extreme cold, disease, starvation,
Law of the minimum
various substances are required for growth.
the one with the lowest concentration will limit
growth ( known as limiting factor)
Limiting Factors can be:
affecting pop regardless of # of individuals
flood, fire, extreme cold, other abiotic factors
affecting pop & dependent on pop size
disease, starvation, predation
State the law of the minimum.
Define limiting factors.
What are some examples of limiting factors?
Density Dependent Factor!
Pops can also be r or K Selected
K - selected
r - selected
K- selected Populations
r- selected Populations
Differentiate between r and K-strategies. Give
2 examples of the types of organisms that use
each of these strategies.