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Chapter Intro-page 90

Chapter Intro-page 90. What You’ll Learn. You will explain how populations grow. You will identify factors that inhibit the growth of populations. You will summarize issues in human population growth. 4.1 Section Objectives – page 91. Section Objectives:.

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Chapter Intro-page 90

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  1. Chapter Intro-page 90 What You’ll Learn You will explain how populations grow. You will identify factors that inhibit the growth of populations. You will summarize issues in human population growth.

  2. 4.1 Section Objectives – page 91 Section Objectives: • Compare and contrast exponential and linear population growth. • Relate the reproductive patterns of different populations of organisms to models of population growth. • Predict effects of environmental factors on population growth.

  3. Section 4.1 Summary – pages 91-99 Principles of Population Growth • A population is a group of organisms, all of the same species, that live in a specific area. • A healthy population will grow and die at a steady rate unless it runs out of food or space, or is attacked in some way by disease or predators. • Scientists study changes in populations in a variety of ways.

  4. Section 4.1 Summary – pages 91-99 Principles of Population Growth • One method involves introducing organisms into an environment that contains abundant resources and then watching how the organisms react.

  5. Section 4.1 Summary – pages 91-99 Principles of Population Growth • Studies of populations of larger organisms, such as an elk population in a national park, require methods such as the use of radio monitors.

  6. Section 4.1 Summary – pages 91-99 How fast do populations grow? • The growth of populations is unlike the growth of pay you get from a job. • Populations of organisms, do not experience linear growth. Rather, the graph of a growing population starts out slowly, then begins to resemble a J-shaped curve.

  7. Section 4.1 Summary – pages 91-99 How fast do populations grow? Population Growth of Houseflies 1 million 500,000 Population size 100 One year

  8. Section 4.1 Summary – pages 91-99 How fast do populations grow? • The initial increase in the number of organisms is slow because the number of reproducing individuals is small. • Soon, however, the rate of population growth increases because the total number of individuals that are able to reproduce has increased.

  9. Section 4.1 Summary – pages 91-99 Is growth unlimited? • A J-shaped growth curve illustrates exponential population growth. • Exponential growth means that as a population gets larger, it also grows at a faster rate. • Exponential growth results in unchecked growth.

  10. Section 4.1 Summary – pages 91-99 What can limit growth? • Limiting factors, such as availability of food, disease, predators, or lack of space, will cause population growth to slow. • Under these pressures, the population may stabilize in an S-shaped growth curve.

  11. Section 4.1 Summary – pages 91-99 What can limit growth? Characteristics of Population Growth PREDA-TORS Exponential growth DISEASE SPACE FOOD Carrying capacity S curve J curve Population 0 Time

  12. Section 4.1 Summary – pages 91-99 Carrying capacity • The number of organisms of one species that an environment can support indefinitely is its carrying capacity. • When a population overshoots the carrying capacity, then limiting factors may come into effect. Click image to view movie.

  13. Section 4.1 Summary – pages 91-99 Carrying capacity • Deaths begin to exceed births and the population falls below carrying capacity. Carrying capacity

  14. Section 4.1 Summary – pages 91-99 Reproduction Patterns • In nature, animal and plant populations change in size. • Biologists study the factor that determines population growth—an organism’s reproductive pattern, also called its life-history pattern. • A variety of population growth patterns are possible in nature.

  15. Section 4.1 Summary – pages 91-99 Rapid life-history patterns • Rapid life-history patterns are common among organisms from changeable or unpredictable environments. • Rapid life-history organisms have a small body size, mature rapidly, reproduce early, and have a short life span.

  16. Section 4.1 Summary – pages 91-99 Slow life-history patterns • Large species that live in more stable environments usually have slow life-history patterns.

  17. Section 4.1 Summary – pages 91-99 Slow life-history patterns • Slow life-history organisms reproduce and mature slowly, and are long-lived. They maintain population sizes at or near carrying capacity.

  18. Section 4.1 Summary – pages 91-99 Density factors and population growth • How organisms are dispersed can be important. • Three patterns of dispersal are random, clumped, and uniform. Clumped Uniform Random

  19. Section 4.1 Summary – pages 91-99 Density factors and population growth • Ecologists have identified two kinds of limiting factors that are related to dispersal: density-dependent and density-independent factors. • Population density describes the number of individuals in a given area.

  20. Section 4.1 Summary – pages 91-99 Density factors and population growth • Density-dependent factors include disease, competition, predators, parasites, and food. • Disease, for example, can spread more quickly in a population with members that live close together.

  21. Section 4.1 Summary – pages 91-99 Density factors and population growth • Density-independent factors can affect all populations, regardless of their density. • Most density-independent factors are abiotic factors, such as temperature, storms, floods, drought, and major habitat disruption.

  22. Section 4.1 Summary – pages 91-99 Organism Interactions Limit Population Size • Population sizes are limited not only by abiotic factors, but also are controlled by various interactions among organisms that share a community.

  23. Section 4.1 Summary – pages 91-99 Predation affects population size • When a predator consumes prey on a large enough scale, it can have a drastic effect on the size of the prey population. • Populations of predators and their prey are known to experience cycles or changes in their numbers over periods of time.

  24. Section 4.1 Summary – pages 91-99 Predation affects population size • The data in this graph reflect the number of hare and lynx pelts sold to the Hudson’s Bay Company in northern Canada from 1845 through 1935. Lynx and Hare Pelts Sold to the Hudson’s Bay Company Lynx Hare Number of organisms(in thousands) Times (in years)

  25. Section 4.1 Summary – pages 91-99 Predation affects population size • In field studies, predation increases the chance that resources will be available for the remaining individuals in a prey population.

  26. Section 4.1 Summary – pages 91-99 Competition within a population • Competition is a density-dependent factor. • When only a few individuals compete for resources, no problem arises. • When a population increases to the point at which demand for resources exceeds the supply, the population size decreases.

  27. Section 4.1 Summary – pages 91-99 The effects of crowding and stress • When populations of certain organisms become crowded, individuals may exhibit symptoms of stress. • As populations increase in size in environments that cannot support increased numbers, individual animals can exhibit a variety of stress symptoms.

  28. Section 4.1 Summary – pages 91-99 The effects of crowding and stress • These include aggression, decrease in parental care, decreased fertility, and decreased resistance to disease. • They become limiting factors for growth and keep populations below carrying capacity.

  29. Section 1 Check Question 1 Exponential growth means that as a population gets larger, it also _____. A. grows at a slower rate B. grows at a faster rate C. grows at a steady rate D. stabilizes in an S-shaped growth curve

  30. Section 1 Check The answer is B. A J-shaped growth curve illustrates exponential growth. Population Growth of Houseflies 1 million Population size 500,000 100 One year

  31. Section 1 Check Question 2 Which of the following would you expect to observe after a population exceeds its carrying capacity? A. population increases exponentially B. births exceed deaths C. deaths exceed births D. population growth rate is unaffected by limiting factors

  32. Section 1 Check The answer is C. Limiting factors may come into effect after a population exceeds its carrying capacity. Deaths begin to exceed births and the population falls below carrying capacity. Characteristics of Population Growth Exponential growth DISEASE PREDATORS SPACE FOOD Carrying capacity S curve J curve Population 0 Time

  33. Section 1 Check Question 3 Offspring per Individual Life Span Organism mosquito 250 1 month elephant 5 70 years humans 2 77 years oak tree 50 100 years A. grows at a slower rate B. grows at a faster rate C. grows at a steady rate D. stabilizes in an S-shaped growth curve

  34. Section 1 Check The answer is A. Rapid life-history organisms have a small body size, mature rapidly, reproduce early, and have a short life span. Offspring per Individual Life Span Organism mosquito 250 1 month elephant 5 70 years humans 2 77 years oak tree 50 100 years

  35. Section 1 Check Question 4 The number of organisms of one species that an environment can support indefinitely is its _____. A. life-history pattern B. growth rate C. demographic D. carrying capacity

  36. Section 1 Check The answer is D. If population size rises above the carrying capacity, more organisms die than are born and the population drops back below the carrying capacity. Carrying capacity

  37. Section 1 Check Question 5 Compare the terms “density-dependent factors” and “density-independent factors”.

  38. Section 1 Check Both are limiting factors for organisms. Density-dependent factors have an increasing effect as the population increases and include disease, competition, parasites, and food. Density-independent factors can affect all populations regardless of density. Most are abiotic factors such as temperature, rainfall, and major habitat destruction.

  39. 4.2 Section objectives– page 100 Section Objectives: • Identify how the birthrate and death rate affect the rate at which a population changes. • Compare the age structure of rapidly growing, slow-growing, and no-growth countries. • Explain the relationship between a population and the environment.

  40. Section 4.2 Summary – page 100-103 World Population • In the United States, a census is taken every ten years. • One of the most useful pieces of data is the rate at which each country’s population is growing or declining. • These figures are the basis for demography, the study of human population size, density and distribution, movement, and its birth and death rates.

  41. Section 4.2 Summary – page 100-103 Human population growth • Human population growth is different because humans have the ability to change their environment. • People live longer and are able to produce offspring that live long enough to produce offspring, hence, a population grows.

  42. Section 4.2 Summary – page 100-103 Calculating growth rate • There are a number of factors that determine population growth rate. • These are births, deaths, immigration and emigration. • Birthrate is the number of live births per 1000 population in a given year.

  43. Section 4.2 Summary – page 100-103 Calculating growth rate • Death rate is the number of deaths per 1000 population in a given year. • Movement of individuals into a population is immigration.

  44. Section 4.2 Summary – page 100-103 Calculating growth rate • Movement out of a population is emigration. • Birthrate – Death rate = Population Growth Rate (PGR) • If the birth rate of a population equals its death rate, then the population growth rate is zero.

  45. Section 4.2 Summary – page 100-103 Calculating growth rate • If the PGR is above zero, more new individuals are entering the population than are leaving, so the population is growing. • A PGR can also be less than zero.

  46. Section 4.2 Summary – page 100-103 Doubling time • Another quantitative factor that demographers look at is the doubling time of a population. • Doubling time is the time needed for a population to double in size. • The time it takes for a population to double varies depending on the current population and growth rate.

  47. Section 4.2 Summary – page 100-103 Doubling time • Doubling time can be calculated for the world, a country, or even a small region, such as a city.

  48. Section 4.2 Summary – page 100-103 Age structure Population Distribution Per Age Range for Several Countries Slow growth Stable growth Rapid growth Reproductive years Male Female Age Population (percent of total for each country)

  49. Section 4.2 Summary – page 100-103 Ecology and growth • The needs of populations differ greatly throughout the world. • Sometimes, a population grows more rapidly than the available resources can handle.

  50. Section Summary – page 100-103 Ecology and growth • Resources that are needed for life, such as food and water, become scarce or contaminated.

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