1. Lesson Overview Lesson Overview How Populations Grow Population Dynamics and Graphs Type of Growth Exponential growth Logistic growth Factors Affecting Growth Birth rates and death rates Immigration and emigration Human population Age Population pyramids Patterns of growth Carrying Capacity Limiting Factors Density-Dependent Predation Competition Human Activity Density-Independent (17.4, 17.8) Seasonal Variations Catastrophic Events Natural Disasters

2. Lesson Overview Lesson Overview How Populations Grow Describing Populations How do ecologists study populations?

3. Lesson Overview Lesson Overview How Populations Grow Describing Populations Researchers study populations’ by: 1.geographic range, 2.density 3.distribution, 4.growth rate, 5.age structure.

4. Lesson Overview Lesson Overview How Populations Grow Describing Populations A population is a group of organisms of a single species that lives in a given area

5. Lesson Overview Lesson Overview How Populations Grow Geographic Range The area inhabited by a population is called its geographic range.

6. Lesson Overview Lesson Overview How Populations Grow Density and Distribution Population density refers to the number of individuals per unit area..

7. Lesson Overview Lesson Overview How Populations Grow Density and Distribution Distribution refers to how individuals in a population are spaced out across the range of the population— 1.randomly, 2.uniformly, 3.clumps.

8. Lesson Overview Lesson Overview How Populations Grow Density and Distribution The dots in the illustration represent individual members of a population with random distribution.

9. Lesson Overview Lesson Overview How Populations Grow Density and Distribution The dots in the illustration represent individual members of a population with uniform distribution.

10. Lesson Overview Lesson Overview How Populations Grow Density and Distribution The tight dots in the illustration represent individual members of a population with clumped distribution.

11. Lesson Overview Lesson Overview How Populations Grow What distribution is shown here?

12. Lesson Overview Lesson Overview How Populations Grow What distribution is shown here?

13. Lesson Overview Lesson Overview How Populations Grow What distribution is shown here?

14. Lesson Overview Lesson Overview How Populations Grow What distribution is shown here? Clump

15. Lesson Overview Lesson Overview How Populations Grow uniform

16. Lesson Overview Lesson Overview How Populations Grow Growth Rate A population’s growth rate ( r ) determines whether the population size increases, decreases, or stays the same. r= (b+i)-(d-e) b= birth in thousands i= immigration in thousands d= death in thousands e= emigration in thousands

17. Lesson Overview Lesson Overview How Populations Grow Population Growth A population will increase or decrease in size depending on how many individuals are added to it or removed from it. The factors that can affect population size are the birthrate, death rate, and the rate at which individuals enter or leave the population.

18. Lesson Overview Lesson Overview How Populations Grow Birthrate and Death Rate A population can grow when its birthrate is higher than its death rate. If the birthrate equals the death rate, the population may stay the same size. If the death rate is greater than the birthrate, the population is likely to shrink.

19. Lesson Overview Lesson Overview How Populations Grow Immigration and Emigration A population may grow if individuals move into its range from elsewhere, a process called immigration. A population may decrease in size if individuals move out of the population’s range, a process called emigration.

20. Lesson Overview Lesson Overview How Populations Grow Age Structure To fully understand a plant or animal population, researchers need to know the population’s age structure—the number of males and females of each age a population contains. Why? Age Structure give insight population growth.

21. Lesson Overview Lesson Overview How Populations Grow Exponential Growth What happens during exponential growth? If you provide a population with all the food and space it needs, protect it from predators and disease, and remove its waste products, the population will grow. Under ideal conditions with unlimited resources, a population will grow exponentially. In exponential growth, the larger a population gets, the faster it grows. The size doubles with each generation of offspring. 2, 4, 8, 16, 32, 64, 128, 256

22. Lesson Overview Lesson Overview How Populations Grow Organisms That Reproduce Slowly Many organisms grow and reproduce much more slowly than bacteria. For example, a female elephant can produce a single offspring only every 2 to 4 years. Newborn elephants take about 10 years to mature. If exponential growth continued and all descendants of a single elephant pair survived and reproduced, after 750 years there would be nearly 20 million elephants!

23. Lesson Overview Lesson Overview How Populations Grow Exponential population growth model In the exponential growth model, population increase over time is a result of the number of individuals available to reproduce without regard to resource limits. In exponential growth, the population size increases at an exponential rate over time, continuing upward as shown in this figure. The line, or curve, you see in the figure shows how quickly a population can grow when it doesn’t face any limiting resources. The line creates a shape like the letter J and is sometimes called a J-curve.

24. Lesson Overview Lesson Overview How Populations Grow Logistic Growth What is logistic growth?

25. Lesson Overview Lesson Overview How Populations Grow Logistic Growth What is logistic growth? Logistic growth occurs when a population’s growth slows and then stops, following a period of exponential growth.

26. Lesson Overview Lesson Overview How Populations Grow Phases of Growth This graph traces the phases of growth that the population goes through.

27. Lesson Overview Lesson Overview How Populations Grow Phase 1: Exponential Growth After a short time, the population begins to grow exponentially. 1.resources are unlimited 2.few individuals die 3.many offspring are produced 4.population size and the rate of growth increase more and more rapidly.

28. Lesson Overview Lesson Overview How Populations Grow Phase 2: Growth Slows Down. growth begins to slow down. The population still grows, but the rate of growth slows down, so the population size increases more slowly. Why does it slow down?

29. Lesson Overview Lesson Overview How Populations Grow Phase 3: Growth Stops. At some point, the rate of population growth drops to zero and the size of the population levels off. Under some conditions, the population will remain at or near this size indefinitely.

30. Lesson Overview Lesson Overview How Populations Grow The Logistic Growth Curve This curve has an S-shape that represents what is called logistic growth. Logistic growth occurs when a population’s growth slows and then stops, following a period of exponential growth. Many familiar plant and animal populations follow a logistic growth curve.

31. Lesson Overview Lesson Overview How Populations Grow Carrying Capacity When the birthrate and the death rate are the same, and when immigration equals emigration, population growth stops. There is a dotted, horizontal line through the region of this graph where population growth levels off. The point at which this dotted line intersects the y-axis represents the carrying capacity.

32. Lesson Overview Lesson Overview How Populations Grow Limiting Factors What factors determine carrying capacity?

33. Lesson Overview Lesson Overview How Populations Grow Limiting Factors What factors determine carrying capacity? Acting separately or together, limiting factors determine the carrying capacity of an environment for a species. Limiting Factors 1. Density-Dependent a. Predation b. Competition c. Human Activity 2. Density-Independent a. Seasonal Variations b. Catastrophic Events c. Natural Disasters

34. Lesson Overview Lesson Overview How Populations Grow Limiting Factors A limiting factor is a factor that controls the growth of a population. Density independent Density dependent

35. Lesson Overview Lesson Overview How Populations Grow Density-Dependent Limiting Factors What limiting factors depend on population density? Density-dependent limiting factors operate strongly only when population density—the number of organisms per unit area—reaches a certain level. These factors do not affect small, scattered populations as much. Density-dependent limiting factors from overcrowding include 1.competition 2.predation affect prey 3.Herbivory affect plants 4.parasitism 5.disease 6.stress from overcrowding

36. Lesson Overview Lesson Overview How Populations Grow Density-Independent Limiting Factors Density-independent limiting factors affect all populations in similar ways, regardless of population size and density. Unusual weather such as hurricanes, droughts, or floods, and natural disasters such as wildfires, can act as density-independent limiting factors.

37. Lesson Overview Lesson Overview How Populations Grow Historical Overview For most of human existence, the population grew slowly because life was harsh. Food was hard to find. Predators and diseases were common and life-threatening.

38. Lesson Overview Lesson Overview How Populations Grow Exponential Human Population Growth Several factors, including improved nutrition, sanitation, medicine, and healthcare, dramatically reduced death rates. Yet, birthrates in most parts of the world remained high. The combination of lower death rates and high birthrates led to exponential growth.

39. Lesson Overview Lesson Overview How Populations Grow The Predictions of Malthus Malthus thought that human populations would be regulated by competition (war), limiting resources (famine), parasitism (disease), and other density-dependent factors. Proven wrong because of science and technological innovations such as medicine and agricultural developments.

40. Lesson Overview Lesson Overview How Populations Grow Patterns of Human Population Growth The scientific study of human populations is called demography. Demography examines characteristics of human populations and attempts to explain how those populations will change over time. Human societies had equally high death rates and birthrates during most of history. But over the past century, population growth in the United States, Japan, and much of Europe slowed dramatically. To explain this shift, demographers hypothesize that these countries have completed the demographic transition, a dramatic change from high birthrates and death rates to low birthrates and death rates.

41. Lesson Overview Lesson Overview How Populations Grow The Demographic Transition The demographic transition is divided into three stages. In Stage I, birthrates and death rates are high for most of history.

42. Lesson Overview Lesson Overview How Populations Grow The Demographic Transition In Stage II, advances in nutrition, sanitation, and medicine lead to lower death rates. Birthrates remain high for a time, so births greatly exceed deaths and the population increases exponentially.

43. Lesson Overview Lesson Overview How Populations Grow The Demographic Transition During Stage III, as the level of education and living standards rise, families have fewer children and the birthrate falls; population growth slows. The demographic transition is complete when the birthrate meets the death rate, and population growth stops.

44. Lesson Overview Lesson Overview How Populations Grow The Demographic Transition So far, the United States, Japan, and Europe have completed the demographic transition. Parts of South America, Africa, and Asia are passing through Stage II. A large part of ongoing human population growth is happening in only ten countries, with India and China in the lead.

45. Lesson Overview Lesson Overview How Populations Grow The Demographic Transition Globally, human population is still growing rapidly, but the rate of growth is slowing down. Our J-shaped growth curve may be changing into a logistic growth curve.

46. Lesson Overview Lesson Overview How Populations Grow Age Structure and Population Growth In the United States, there are nearly equal numbers of people in each age group. This age structure (coke bottle) predicts a slow but steady growth rate for the near future.

47. Lesson Overview Lesson Overview How Populations Grow Age Structure and Population Growth In Mexico, on the other hand, there are many more young children than teenagers, and many more teenagers than adults. This age structure predicts a population that will double in about 30 years.

48. Lesson Overview Lesson Overview How Populations Grow