Populations

1. Populations Honors Biology – Chapter 5

2. What is a Population? • A group of the same species living in a given area • It is populations or organisms that interact in ecosystems • Example:

3. An Introduction – Sea Otters of the Pacific Northwest • Live in kelp forest community

4. An Introduction – Sea Otters of the Pacific Northwest • Sea urchins as food • Sea urchins eat kelp • Sea otters nearly eliminated due to hunting • Sea urchin populations rise • Kelp forests decline • Restoring balance: Sea otters declared endangered – protected from hunting

5. Predator/Prey Popluation Relationships • Hare / Lynx • Hare population goes up • Lynx population goes up • Lots of food (hares) available • Causes hare population to go down • More lynx = more predation on hares • Causes lynx population to go down • Hare population decrease means less food for lynx and they die

6. Hare/Lynx

7. 4 Characteristics of Populations • Geographic distribution • Range • Area inhabited by a population • Density • Number of individuals per unit area • Growth rate • Age structure

8. Population Growth • 3 factors affect population size • Number of births • natality • Number of deaths • mortality • Number of individuals that enter or leave a population • Immigration - enter • Emigration - leave

9. Population Growth • A population will increase or decrease in size depending on how many individuals are added to it or removed from it • Growth occurs if • More individuals are born than die • If birth rate equals death rate the population will stay near the same size

10. Movement into or out of a population • May be caused by • Young animals mature and leave the area • Shortage of food in an area

11. Exponential Growth • Individuals in a population reproduce at a constant rate • Initially, growth is slow • Overtime the population becomes larger and large until it approaches an infinitely large size • Ideal conditions with unlimited resources required

12. Bacteria • Fastest rates of reproduction among living things • 20 minutes for population to double • Why don’t they take over the Earth? • NOT unlimited resources

13. Logistic Growth • Growth pattern that occurs when a population’s growth slows or stops following a period of exponential growth. • Things that slow a population’s growth • Natality (birth rate) decreases • Mortality (death rate) increases • Rate of immigration decreases • Rate of emigration increases

14. Logistic Growth • Also, when birth and death rates are the same, the population growth will slow or even stop for a time • Even when a population stops “growing”, the population is still rising and falling somewhat – though the ups and downs average out to the same population size.

15. Logistic Growth Curve • Slow growth • Exponential growth • Growth levels off • Carrying Capacity • K • Dotted line • The maximum number of individuals that an environment can support

16. Limits to Growth • Limiting Factors • Factors that cause population growth to decrease • Competition • Predation • Parasitism • Drought • Human disturbance

17. There are TWO types of limiting factors • Density Dependent • Density Independent

18. Density Dependent Limiting Factors • Depends on the size of a population • Usually greatest impact when the population is large and dense • Include • Competition • Predation • Parasitism • Disease

19. Density Independent Limiting Factors • Affects all populations (large or small) in similar ways. • Unusual weather • Natural disasters • Human activities • Like Habitat Destruction

20. Human Population Growth • Like other populations of organisms, the human population tends to increase with time.

21. Human Population Growth Curve • Initially slow • Food scarce • Life harsh • 500 years ago • More rapid growth • Currently EXPONENTIAL • Why? • Agriculture and industry advances • Food supply increased • Improved sanitation • Medicine

22. Human Population Growth Curve

23. Demography • The study of human populations • Examines human populations and tries to predict how they will change over time.

24. Demographic Transition • Population growth in some countries has slowed • U.S. • Japan • Much of Europe • Why? • Hypothesis: These countries have completed the “demographic transition

25. Demographic Transition • A dramatic change in birth and death rates • What happens • Initially both birth and death rates high • Advances in nutrition, etc. lower death rate • Population increases rapidly • Societies modernize – increase education, etc. • Families have fewer children • Birthrate falls to meet the death rate • Population growth stops

26. Populations that have NOT completed the demographic transition • Most countries • India • China

27. Age Structure Diagrams • Shows how many people of different ages and genders are in a population • Useful in predicting future population growth

28. Age Structure Diagram

29. Predicting Future Population Growth • Factors to consider • Age structure of each country • Prevalence of life-threatening diseases • Predictions for 2050 • 9 billion people on Earth

30. Effects of Human Population Growth • Some scientists suggest if human population growth rate does not become LESS than 0 (deaths outnumber births) • Serious damage to environment • Serious damage to global economy • Some economists say that technology advances and changes in societies can control negative impacts