1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 How Populations Change in Size Objectives Describe the three main properties of a population. Describe exponential population growth. Describe how the reproductive behavior of individuals can affect the growth rate of their population. Explain how population sizes in nature are regulated. Chapter 8

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 How Populations Change in Size Learning Log - Predicting Populations Refer to page 210 in your Textbook. Orcas (killer whales) in this photograph hunt and eat sea lions. Would a change in the number of sea lions have an effect on the orcas? Would it make a difference if the sea lions were the only food source for the orcas? What other reasons might the number of sea lions or orcas change? Chapter 8

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 How Populations Change in Size Learning Log - Predicting Populations Refer to page 210 in your Textbook. Orcas (killer whales) in this photograph hunt and eat sea lions. Would a change in the number of sea lions have an effect on the orcas? Would it make a difference if the sea lions were the only food source for the orcas? What other reasons might the number of sea lions or orcas change? Chapter 8

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu What Is a Population? A population is a group of organisms of the same species that live in a specific geographical area and interbreed. The word population refers to the group in general and also to the size of the population. Chapter 8 Section 1 How Populations Change in Size

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Properties of Populations Density is the number of individuals of the same species in that live in a given unit of area. Dispersion is the pattern of distribution of organisms in a population. A population’s dispersion may be even, clumped, or random. Population can be described in terms of size, density, dispersion. Chapter 8 Section 1 How Populations Change in Size

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How Does a Population Grow? A population gains individuals with each new offspring or birth and loses them with each death. The resulting population change over time can be represented by the equation below. Chapter 8 Section 1 How Populations Change in Size

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How Does a Population Grow? Growth rate is an expression of the increase in the size of a population over a given period of time. (Birth rate minus death rate) Overtime, the growth rates of populations change because birth rates and death rates increase or decrease. For this reason, growth rates can be positive, negative, or zero. Chapter 8 Section 1 How Populations Change in Size

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How Does a Population Grow? When growth rate is zero, the average number of births equals the average number of deaths. A population would remain the same size if each pair of adults produced exactly two offspring, and each of those offspring survived to reproduce. If the adults in a population are not replaced by new births, the growth rate will be negative and the population will shrink. Chapter 8 Section 1 How Populations Change in Size

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How Fast Can a Population Grow? Populations usually stay about the same size from year to year because various factors kill many individuals before they can reproduce. These factors control the sizes of populations. In the long run, the factors also determine how the population evolves. Chapter 8 Section 1 How Populations Change in Size

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reproductive Potential A species’ biotic potential is the fastest rate at which its populations can grow. This rate is limited by reproductive potential. Reproductive potential is the maximum number of offspring that a given organism can produce. (Some species have much higher reproductive potentials than others. Darwin calculated that it could take 750 years for a pair of elephants to produce 19 million descendants. While bacteria could produce that in a few days or weeks.) Chapter 8 Section 1 How Populations Change in Size

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reproductive Potential Reproductive potential increases when individuals produce more offspring at a time, reproduce more often, and reproduce earlier in life. Reproducing earlier in life has the greatest effect on reproductive potential. Chapter 8 Section 1 How Populations Change in Size

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reproductive Potential R-selective –Small organisms, (e.g. bacteria and insects) can reproduce when they are only a few hours or a few days old. –As a result, their populations can grow quickly. K-selective –large organisms, (e.g. elephants and humans) become sexually mature after a number of years and therefore have a much lower reproductive potential than insects. Chapter 8 Section 1 How Populations Change in Size

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 How Populations Change in Size Learning Log Types of Growth. You have been offered a new job with 2 salary options: 1) receive $10 a week with a $5 per week raise; 2) receive one penny for your first day, and double the previous day’s pay for each of the remaining 30 days Calculate each monthly salary Which option would you prefer? Chapter 8

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Exponential Growth Exponential growth is logarithmic growth or growth in which numbers increase by a certain factor in each successive time period. Exponential growth occurs in nature only when populations have unlimited resources (food, space, no competition). For example, population explosions occur when bacteria or molds grow on a new source of food. Chapter 8 Section 1 How Populations Change in Size

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Exponential Growth In exponential growth, a large number of individuals is added to the population in each succeeding time period. Chapter 8 Section 1 How Populations Change in Size

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Population Change & Exponential Growth Chapter 8 Section 1 How Populations Change in Size

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 How Populations Change in Size Learning Log Limited Resources. Conduct the activity then answer the following questions. What problems occur when the white space is depleted? How would this affect population? Chapter 8

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu What Limits Population Growth? Because natural conditions are neither ideal nor constant, populations cannot grow forever. Eventually, resources are used up or the environment changes, and deaths increase or births decrease. Chapter 8 Section 1 How Populations Change in Size

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Carrying Capacity Carrying capacity is the largest population that an environment can support at any given time. A population may increase beyond this number but it cannot stay at this increased size. Because ecosystems change, carrying capacity is difficult to predict or calculate exactly. However, it may be estimated by looking at average population sizes or by observing a population crash after a certain size has been exceeded. Chapter 8 Section 1 How Populations Change in Size

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Populations Changes & Carrying Capacity Chapter 8 Section 1 How Populations Change in Size

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Resource Limits A species reaches its carrying capacity when it consumes a particular natural resource at the same rate at which the ecosystem produces the resource. That natural resource is then called a limiting resource. The supply of the most severely limited resources determines the carrying capacity of an environment for a particular species at a particular time. Chapter 8 Section 1 How Populations Change in Size

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Competition Within a Population The members of a population use the same resources in the same ways, so they will eventually compete with one another as the population approaches its carrying capacity. Instead of competing for a limiting resource, members of a species may compete indirectly for social dominance or for a territory. Competition within a population is part of the pressure of natural selection. Chapter 8 Section 1 How Populations Change in Size

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Competition Within a Population A territory is an area defended by one or more individuals against other individuals. The territory is of value not only for the space but for the shelter, food, or breeding sites it contains. Many organisms expend a large amount of time and energy competing with members of the same species for mates, food, or homes for their families. Chapter 8 Section 1 How Populations Change in Size

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 How Populations Change in Size Learning Log Growth Rate. rN =  N growth rate = change in pop.  t time What does this equation mean in English? How does the r-value relate to the equation? What does this equation tell us about populations with high r- values? Do the Math Practice on page 215 in your textbook Chapter 8

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Two Types of Population Regulation Population size can be limited in ways that may or may not depend on the density of the population. Causes of death in a population may be density dependent or density independent. Chapter 8 Section 1 How Populations Change in Size

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Population Regulation When a cause of death in a population is density dependent, deaths occur more quickly in a crowded population than in a sparse population. This type of regulation happens when individuals of a population are densely packed together. Limited resources, predation and disease result in higher rates of death in dense populations than in sparse populations. Chapter 8 Section 1 How Populations Change in Size

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Population Regulation When a cause of death is density independent, a certain proportion of a population may die regardless of the population’s density. This type of regulation affects all populations in a general or uniform way. Severe weather and natural disasters are often density independent causes of death. Chapter 8 Section 1 How Populations Change in Size

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 How Populations Change in Size Learning Log Population Regulation. Do the activity and answer the questions? Describe the first scenario.What kind of regulation does this represent? Describe the second scenario. What kind of regulation does this represent? Chapter 8