1. Topic 2: Ecosystems
2.3: Changes
Population growth
• As long as their is a plentiful
supply of resources populations
grow
• We can define population growth
as:
• A change in numbers with a
change in time

2. Topic 2: Ecosystems
2.3: Changes
Exponential growth
Bacterial Growth
120
• But we know that population
growth is not simple 100
Number of cells / ml
80
• If we put some bacteria cells in a
60
culture - the bacteria reproduce
exponentially 40
•
20
As the population grows so to
does the rate of growth 0
0 50 100 150 200 250 300
Time (min)

3. Topic 2: Ecosystems
2.3: Changes
Exponential growth
Population
120
• This is an example of positive
feedback 100
80
• The curve produced is sometimes
60
called a J-curve
Growth
40
• The J curve assumes that there is 20
no limit on resources
0
0 50 100 150 200 250 300
Time

4. Topic 2: Ecosystems
2.3: Changes
Exponential growth
• This can also be modeled as a
mathematical equation
• so if the population increased by
4% every generation then
population rN = 0.04 x N

5. Topic 2: Ecosystems
2.3: Changes
Exponential growth and
Carrying Capacity
• Darwin calculated that if you
started with two elephants and
exponential growth, after 700
years the world population of
elephants would be 19 000 000
• This obviously hasn’t happened

6. Topic 2: Ecosystems
2.3: Changes
Exponential growth and
Carrying Capacity
• The size of a population is limited
by available resources and
competition for them
• This results in a maximum
population size that an
environment can sustain
• The Carrying Capacity

7. Topic 2: Ecosystems
2.3: Changes
Exponential growth and
Bacterial Growth
Carrying Capacity 120
• The carrying capacity is around 100
Number of cells / ml
120 bacterial cells / ml 80
• Negative feedback operates
60
keeping the population around the 40
Carrying capacity
20
• Ecologists use K to represent 0
0 100 200 300 400 500 600
carrying capacity Time (min)

8. Topic 2: Ecosystems
2.3: Changes
Exponential growth and
Carrying Capacity K 120
Population
• This produces an S or Sigmoid 100
curve 80
60
Growth
40
20
0
0 100 200 300 400 500 600
Time

9. Topic 2: Ecosystems
2.3: Changes
Exponential growth and
Carrying Capacity
• This can also be modeled as a
mathematical equation and is
called the logistic equation
• It includes a component that slows
population growth at a certain
point - K the Carrying capacity

10. Topic 2: Ecosystems
2.3: Changes
Phases in Logistic growth Stationary
120
Log
• Lag phase: population grows slowly
(environmental adaption) 100
•
80
Exponential or Log phase:
Population grows rapidly exploiting 60
a plentiful resource supply (maximal 40
growth) Lag
20
• Stationary phase: Population growth
0
reaches a plateau - the maximum 0 100 200 300 400 500 600
population size under the
environmental conditions

11. Topic 2: Ecosystems
2.3: Changes
A Question
• The Red Kite (Milvus milvus)used to
be a very common bird in Britain
but it became extinct in England
through human persecution. A small
population survived in the remote
hills of mid-Wales. Between 1989
and 1994, wild kites from Spain
were imported and released into
the Chiltern Hills

12. Topic 2: Ecosystems
2.3: Changes
A Question
Untitled 1
1. Suggest why the number of Red
Kites is increasing in the
Number of breeding pairs
Chilterns.
2. It is hoped that the Red Kite
population in the wild will
eventually reach the carrying
capacity. Explain what is meant
by the term carrying capacity.
Introductions stopped