1. Chapter 14 “Populations” n 14.1 “Populations and How They Grow” n Objective: –Describe the different ways that populations may change.

2. Populations n A group of organisms of a single species that live in a given area.

3. Changes in Population Size n In nature populations will stay relatively the same in number. n HOWEVER, sometimes those numbers will change dramatically.

4. Growth Rate n A change in population size. (+ or -) n Depends on how many organisms are added and removed (immigration & emigration). n AND interaction between organisms.

5. Why do Populations Grow? n Ideal conditions (adequate food supply, shelter, protection from predators) = growth. n Birth rates are higher than death rates.

6. Mexican Population Growth

7. Baby Boom n If ideal conditions continue, the larger the population gets, the faster it grows. n Exponential Growth = constant growth that takes place under ideal conditions.

8. Exponential Growth in Bacteria

9. Growth with Limits n In nature, exponential growth does not continue forever. n Growth slows down because resources are limited.

10. Growth with Limits Carrying Capacity

11. Growth Limits continued... n Zero Population Growth –birth rate and death rate are the same –population stays the same = steady-state n Carrying Capacity –the largest # of individuals of a population that a given environment can support

12. Boom & Bust n In nature species increase in # until they reach their carrying capacity. n Some however reach a “boom” and then crash in size “the bust”.

13. Boom and Bust

14. 14.2 “Why Populations Stop Growing” n Objective: –Identify the factors that control population growth in nature.

15. Population Growth n Limited by the size and density of a population. n Population Density = the # of organisms in a given area. n Limiting Factor = a factor that causes a population to decrease.

16. Density-Dependent Limiting Factors n Depends on population size, affects large & dense pops more. n Include: –Competition –Predation –Parasitism –Disease –Crowding & Stress

17. Competition n When populations become too crowded, organisms will compete for resources. n Can occur between different species = evolutionary change. n Increases death rates.

18. Predation n Predator-Prey relationship controls populations. n Defenses for both predator & prey.

19. Predator Prey Graph

20. Parasitism n Range in size from microscopic (bacteria) to tapeworms (30+ cm). n Like predators, parasites take nourishment at the expense of their hosts. n Host-specific.

21. Parasites – tapeworm

22. Crowding and Stress n Most organisms need a certain amount of space. n Overcrowding causes disturbances among organisms leading to weakening.

23. Density-Independent Limiting Factors n Affects populations regardless of size. n Some examples include: n unusual weather n seasonal cycles n human activities: –damming rivers –clear-cutting forests

24. Clear Cut Forest