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# Population Dynamics

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### Population Dynamics

1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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