Copyright Pearson Prentice Hall 5-1 How Populations Grow Photo Credit: © Frans Lanting/Minden Pictures, Inc. Copyright Pearson Prentice Hall

Characteristics of Populations What characteristics are used to describe a population? Copyright Pearson Prentice Hall

Characteristics of Populations Three important characteristics of a population are its: geographic distribution population density growth rate Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Population Growth What factors affect population size? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Population Growth Population Growth Three factors can affect population size: the number of births the number of deaths the number of individuals that enter or leave the population A population can grow when its birthrate is greater than its death rate. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Population Growth Immigration, the movement of individuals into an area, is another factor that can cause a population to grow. Emigration, the movement of individuals out of an area, can cause a population to decrease in size. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Exponential Growth What are exponential growth and logistic growth? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Exponential Growth Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially. Exponential growth occurs when the individuals in a population reproduce at a constant rate. The population becomes larger and larger until it approaches an infinitely large size. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Exponential Growth Exponential Growth In the presence of unlimited resources and in the absence of predation and disease, a population will grow exponentially. Both hypothetical graphs show the characteristic J-shape of exponential population growth. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Logistic Growth Logistic Growth As resources become less available, the growth of a population slows or stops. Logistic growth occurs when a population's growth slows or stops following a period of exponential growth. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Logistic growth is characterized by an S-shaped curve. This graph shows the S-shaped curve of logistic growth. As resources become less available, the population growth rate slows or stops. The growth of this population has leveled off at its carrying capacity. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Limiting Factors What factors limit population growth? Copyright Pearson Prentice Hall

Density-Dependent Factors Wolf and Moose Populations on Isle Royale The relationship between moose and wolves on Isle Royale illustrates how predation can affect population growth. In this example, the moose population was also affected by changes in food supply, and the wolf population was also affected by disease. Moose Wolves Density-Dependent Activity Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-1 Population density is the number of individuals that are born each year. per unit area. that immigrate. that emigrate. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-1 When the birthrate of a population exceeds its death rate, the population decreases. increases. stays the same. increases then decreases. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-1 An S-shaped curve on a graph of population growth is characteristic of exponential growth. logistic growth. carrying capacity. delayed growth. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-1 Exponential growth in a population slows down or stops as resources become limited. rate of immigration increases. rate of emigration decreases. birth rate increases. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-1 Exponential growth rate means that each new generation of a population adds the same number of new individuals as the previous generation did. increases at the same rate as the previous generation. is the same size as the generation before. increases by a varying amount. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-2 Limits to Growth Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Limiting Factors What factors limit population growth? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Limiting Factors Limiting Factors The primary productivity of an ecosystem can be reduced when there is an insufficient supply of a particular nutrient. Ecologists call such substances limiting nutrients. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Limiting Factors A limiting nutrient is an example of a more general ecological concept: a limiting factor. In the context of populations, a limiting factor is a factor that causes population growth to decrease. Copyright Pearson Prentice Hall

Density-Dependent Factors A limiting factor that depends on population size is called a density-dependent limiting factor. Copyright Pearson Prentice Hall

Density-Dependent Factors Density-dependent limiting factors include: competition predation parasitism disease Copyright Pearson Prentice Hall

Density-Dependent Factors Density-dependent factors operate only when the population density reaches a certain level. These factors operate most strongly when a population is large and dense. They do not affect small, scattered populations as greatly. Copyright Pearson Prentice Hall

Density-Dependent Factors Competition When populations become crowded, organisms compete for food, water space, sunlight and other essentials. Competition among members of the same species is a density-dependent limiting factor. Copyright Pearson Prentice Hall

Density-Dependent Factors Competition can also occur between members of different species. This type of competition can lead to evolutionary change. Over time, the species may evolve to occupy different niches. Copyright Pearson Prentice Hall

Density-Dependent Factors Predation Populations in nature are often controlled by predation. The regulation of a population by predation takes place within a predator-prey relationship, one of the best-known mechanisms of population control. Copyright Pearson Prentice Hall

Density-Dependent Factors Wolf and Moose Populations on Isle Royale The relationship between moose and wolves on Isle Royale illustrates how predation can affect population growth. In this example, the moose population was also affected by changes in food supply, and the wolf population was also affected by disease. Moose Wolves Copyright Pearson Prentice Hall

Density-Dependent Factors Parasitism and Disease Parasites can limit the growth of a population. A parasite lives in or on another organism (the host) and consequently harms it. Copyright Pearson Prentice Hall

Density-Independent Factors Density-independent limiting factors affect all populations in similar ways, regardless of the population size. Copyright Pearson Prentice Hall

Density-Independent Factors Examples of density-independent limiting factors include: unusual weather natural disasters seasonal cycles certain human activities—such as damming rivers and clear-cutting forests Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-2 A limiting factor that affects all populations in similar ways regardless of their size might be drought. disease. predation. crowding. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-2 Which of the following would be a limiting factor affecting the panda population of China? programs that educate people about endangered species capture of some pandas for placement in zoos laws protecting habitat destruction a disease that kills bamboo plants Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-2 Density-dependent factors operate most strongly when a population is large and dense. large but sparse. small and sparse. small, but growing. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-2 Within a limited area, if the population of a predator increases, the population of its prey is likely to increase. decrease. remain about the same. become extinct. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-2 Which of the following is a density-independent factor affecting populations? predation disease a destructive hurricane parasites Copyright Pearson Prentice Hall

5-3 Human Population Growth Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Historical Overview How has the size of the human population changed over time? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Historical Overview Historical Overview Like the populations of many other living organisms, the size of the human population tends to increase with time. For most of human existence, the population grew slowly. Limiting factors kept population sizes low. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Historical Overview About 500 years ago, the human population began growing more rapidly. Life was made easier and safer by advances in agriculture and industry. Death rates were dramatically reduced due to improved sanitation, medicine, and healthcare, while birthrates remained high. Copyright Pearson Prentice Hall

Human Population Growth Copyright Pearson Prentice Hall Historical Overview With these advances, the human population experienced exponential growth. Human Population Growth The size of the human population has increased over time. After a long, slow start, the worldwide population grew exponentially following improvements in medicine, sanitation, agriculture, energy use, and technology. Copyright Pearson Prentice Hall

Patterns of Population Growth The scientific study of human populations is called demography. Demography examines the characteristics of human populations and attempts to explain how those populations will change over time. Copyright Pearson Prentice Hall

Patterns of Population Growth Why do population growth rates differ in countries throughout the world? Copyright Pearson Prentice Hall

Patterns of Population Growth Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly. Copyright Pearson Prentice Hall

Patterns of Population Growth The Demographic Transition Over the past century, population growth in the United States, Japan, and much of Europe has slowed dramatically. According to demographers, these countries have completed the demographic transition, a dramatic change in birth and death rates. Copyright Pearson Prentice Hall

Patterns of Population Growth The demographic transition has three stages. In stage 1, there are high death rates and high birthrates. In stage 2, the death rate drops, while the birthrate remains high. The population increases rapidly. In stage 3, the birthrate decreases, causing population growth to slow. Copyright Pearson Prentice Hall

Patterns of Population Growth The demographic transition is complete when the birthrate falls to meet the death rate, and population growth stops. Birthrates, death rates, and the age structure of a population help predict the rate of population growth. Birthrates and death rates fall during the demographic transition. In Stage I, both the birthrate and death rate are high. During Stage II, the death rate drops while the birthrate remains high. Finally, in Stage III, the birthrate also decreases. Copyright Pearson Prentice Hall

Patterns of Population Growth Age Structure Population growth depends, in part, on how many people of different ages make up a given population. Demographers can predict future growth using models called age-structure diagrams. Age-structure diagrams show the population of a country broken down by gender and age group. Copyright Pearson Prentice Hall

Patterns of Population Growth U.S. Population In the United States, there are nearly equal numbers of people in each age group. This age structure diagram predicts a slow but steady growth rate for the near future. 80+ Males Females 60–64 Age (years) 40–44 This graph shows the age structure of the U.S. population. 20–24 0–4 8 6 4 2 0 2 4 6 8 Percentage of Population Copyright Pearson Prentice Hall

Patterns of Population Growth Rwandan Population In Rwanda, there are many more young children than teenagers, and many more teenagers than adults. This age structure diagram predicts a population that will double in about 30 years. 80+ Males Females 60–64 Age (years) 40–44 This graph shows the age structure of the Rwandan population. 20–24 0–4 Percentage of Population Copyright Pearson Prentice Hall

Future Population Growth To predict human population growth, demographers must consider the age structure of each country, as well as the prevalence of life-threatening diseases. If growing countries move toward the demographic transition, growth rate may level off or decrease. Copyright Pearson Prentice Hall

Future Population Growth This table, based on actual and projected data from the U.S. Census Bureau, International Database, shows data on world population. Copyright Pearson Prentice Hall

Future Population Growth Ecologists suggest that if growth does not slow down, there could be serious damage to the environment and global economy. Economists assert that science, technology, and changes in society may control the negative impact of population growth. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-3 The size of the human population began to increase exponentially after the bubonic plague. development of plowing and irrigation. Industrial Revolution. development of the first cities. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-3 Which of the following is NOT a potential limiting factor of human population growth? famine medicine war disease Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-3 After the demographic transition is complete, a population grows rapidly. grows slowly. begins a period of rapid decline. stays about the same size as time passes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-3 An age-structure diagram shows a breakdown of a population by location and age group. age group and gender. birthrate and death rate. age group and emigration rate. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-3 Since the mid-1960s, the average annual growth rate of the human population has remained about the same. failed to show a consistent pattern. increased. decreased. Copyright Pearson Prentice Hall