2. Populations and interactions Population Growth Curves Sixth Form

3. Populations and interactions Population Growth Curves Aims for the lesson Understand the sigmoidal growth curve of bacteria Understand the limiting factors on the size of a population Understand the term carrying capacity

4. Populations and interactions Population Size Population = number of organisms of the same species that live in the same place at the same size and can interbreed Numbers can vary for a variety of reasons These reasons can be difficult to understand

5. Populations and interactions Sigmoidal Growth Curve There are key phases Lag phase Log phase Stationary phase Decline or death phase

6. Populations and interactions Sigmoidal Growth Curve Make notes of the causes of each of the key phases. You must explain why the rate of growth is changing for each of these phases The reason the curve is S shaped and that is why it is caused sigmoid

7. Populations and interactions Bacterial Growth Eventually the bacteria will grow until a factor limits growth Amazingly these are called limiting factors!!

8. Populations and interactions Limiting Factors Limiting factors in growth culture? Amounts of nutrients Levels of excretory factors In the wild a variety of factors may be limiting

9. Populations and interactions Limiting Factors More complex than bacteria Will also need nesting sites Effect of predators and parasites All of the above will put an upper limit on numbers –carrying capacity

10. Populations and interactions Carrying Capacity Unlike the bacteria in the flask, food never totally runs out Environmental factors affect numbers Such as the weather Difficult to control all facts when we study population sizes

11. Populations and interactions Population Growth Homework Choose a species and briefly outline it’s habitat List the limiting factors of the carrying capacity of the habitat