35-1 & 35-2 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 density growth rate Copyright Pearson Prentice Hall

Characteristics of Populations Geographic distribution, or range, describes the area inhabited by a population. Population density is the number of individuals per unit area. Growth rate is the increase or decrease of the number of individuals in a population over time. 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. Populations can increase by immigration as animals in search of mates or food arrive from outside. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Population Growth Emigration, the movement of individuals out of an area, can cause a population to decrease in size. Emigration can occur when animals leave to find mates and establish new territories. A shortage of food in one area may also lead to emigration. 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 In nature, exponential growth does not continue in a population for very long. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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 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 Logistic Growth Carrying Capacity The largest number of individuals of a population that a given environment can support is called its carrying capacity. When a population reaches the carrying capacity of its environment, its growth levels off. The average growth rate is zero. 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 5-2 Limits to Growth Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-2 Limits to Growth Limiting Factors What factors limit population growth? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5-2 Limits to Growth Limiting Factors Limiting Factors In the context of populations, a limiting factor is a factor that causes population growth to decrease. Copyright Pearson Prentice Hall

Density-Dependent Factors 5-2 Limits to Growth Density-Dependent Factors 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 5-2 Limits to Growth Density-Dependent Factors Density-dependent limiting factors include: competition predation parasitism disease Copyright Pearson Prentice Hall

Density-Dependent Factors 5-2 Limits to Growth 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 5-2 Limits to Growth 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 5-2 Limits to Growth 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 . . . or one species will move or die out. Copyright Pearson Prentice Hall

Density-Dependent Factors 5-2 Limits to Growth 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 5-2 Limits to Growth 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 5-2 Limits to Growth 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 5-2 Limits to Growth Density-Independent Factors 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 5-2 Limits to Growth 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 5-1 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 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

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