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12.2: Characteristics of Population

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Lesson 12.2: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. A clumped population distribution always has more individuals than a uniform distribution.

_____ 2. Population growth rate is how fast a population changes in size over time.

_____ 3. A population's age-sex structure influences population growth, as older people are more likely to reproduce.

_____ 4. Dispersal refers to offspring moving away from their parents.

_____ 5. With a type I survivorship curve, most of the offspring survive to adulthood so they can reproduce.

_____ 6. Populations gain individuals through births and emigration.

_____ 7. Logistic growth levels out at the carrying capacity.

_____ 8. K-selected population growth is controlled by density-dependent factors.

_____ 9. Most populations live under ideal conditions, so they grow at exponential rates.

_____ 10. Immigration is the regular movement of individuals or populations each year during certain seasons.

_____ 11. The carrying capacity is the largest population size that can be supported in an area without harming the environment.

_____ 12. With a type III survivorship curve, parents produce moderate numbers of offspring and provide some parental care.

_____ 13. With a random population distribution, organisms are clustered together in groups.

_____ 14. A positive population growth rate means a population is increasing.

_____ 15. Species that live in unstable environments are usually r-selected, and their population size is usually well below the carrying capacity.

Lesson 12.2: Critical Reading

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Patterns of Population Growth

Populations may show different patterns of growth. The growth pattern depends partly on the conditions under which a population lives.

Exponential Growth

Under ideal conditions, populations of most species can grow at exponential rates. Curve A in the graph below represents exponential growth. The population starts out growing slowly. As population size increases, the growth rate also increases. The larger the population becomes, the faster it grows.

Exponential and Logistic Growth. Curve A shows exponential growth. Curve B shows logistic growth. (Image courtesy of CK-12 Foundation and under the Creative Commons license CC-BY-NC-SA 3.0.)

Logistic Growth

Most populations do not live under ideal conditions. Therefore, most do not grow exponentially. Certainly, no population can keep growing exponentially for very long. Many factors may limit growth. Often, the factors are density-dependent. These are factors that kick in when the population becomes too large and crowded. For example, the population may start to run out of food or be poisoned by its own wastes. As a result, population growth slows and population size levels off. Curve B in graph above represents this pattern of growth, which is called logistic growth.

At what population size does growth start to slow in the logistic model of growth? That depends on the population’s carrying capacity (see graph above). The carrying capacity (K) is the largest population size that can be supported in an area without harming the environment. Population growth hits a ceiling at that size in the logistic growth model.

K-Selected and r-Selected Species

Species can be divided into two basic types when it comes to how their populations grow.

  • Species that live in stable environments are likely to be K-selected. Their population growth is controlled by density-dependent factors. Population size is generally at or near the carrying capacity. These species are represented by curve B in the graph above.
  • Species that live in unstable environments are likely to r-selected. Their potential population growth is rapid. For example, they have large numbers of offspring. However, individuals are likely to die young. Thus, population size is usually well below the carrying capacity. These species are represented by the lower part of curve A in the graph above.

Questions

1. What is exponential growth?

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2. What is logistic growth?

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3. What is the carrying capacity?

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4. Define K- selected and r-selected. What is the main difference between them?

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Lesson 12.2: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. Which would represent a population?
    1. All the fish in an aquarium.
    2. All the dogs in your neighborhood.
    3. All the animals in the local zoo.
    4. all of the above
  2. The age-sex structure of a quickly growing population would probably have
    1. a wide base, showing many young individuals.
    2. a wide top, showing many older individuals.
    3. a wide middle area, showing many middle-aged individuals.
    4. all of the above
  3. Humans have a type ______ survivorship curve, as ________________.
    1. II, parents produce moderate numbers of children.
    2. III, most of the offspring survive to adulthood so they can reproduce.
    3. I, most of the offspring survive to adulthood so they can reproduce.
    4. I, parents produce moderate numbers of children.
  4. Population growth can be represented by the equation r =
    1. (b + e) - (d + i)
    2. (b + i) - (d + e)
    3. (b + d) - (i + e)
    4. (d + i) - (b + e)
  5. During exponential growth,
    1. the larger the population becomes, the slower it grows.
    2. population growth eventually slows and population size levels off.
    3. as population size increases, the growth rate also increases.
    4. all of the above
  6. The carrying capacity of a population
    1. is reached as resources become limiting.
    2. is reached at the end of exponential growth.
    3. is reached in r-selected populations.
    4. is reached when the environment begins to be harmed.
  7. Which of the following are examples of density-dependent factors? (1) food, (2) disease, (3) rainfall, (4) temperature.
    1. 1 only
    2. 1 and 2
    3. 1, 2, and 3
    4. 1, 2, 3, and 4
  8. When organisms must compete for resources, they will usually have a ____________ distribution.
    1. uniform
    2. random
    3. clumped
    4. competitive

Lesson 12.2: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.

Definitions

_____ 1. represents the age-sex structure of a population

_____ 2. coming into the population from somewhere else

_____ 3. population growth under limiting conditions

_____ 4. the average number of individuals in a population per unit of area or volume

_____ 5. species whose population size is usually well below the carrying capacity

_____ 6. leaving the population for another area

_____ 7. the largest population size that can be supported in an area without harming the environment

_____ 8. graphs that represent the number of individuals still alive at each age

_____ 9. population growth under ideal conditions

_____ 10. how fast a population changes in size over time

_____ 11. species whose population growth is controlled by density-dependent factors

_____ 12. the regular movement of individuals or populations each year during certain seasons

Terms

a. carrying capacity

b. emigration

c. exponential growth

d. immigration

e. K-selected

f. logistic growth

g. migration

h. population density

i. population growth rate

j. population pyramid

k. r-selected

l. survivorship curve

Lesson 12.2: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. The population is the unit of natural selection and ____________.

2. The purpose of migration usually is to find food, mates, or other ____________.

3. Species that live in ____________ environments are likely to be K-selected.

4. Population ____________ may be clumped, random, or uniform.

5. The carrying capacity is the ____________ population size that can be supported in an area.

6. A ____________ curves represents the number of individuals still alive at each age.

7. The two main factors affecting population ____________ are the birth rate and death rate.

8. The age-sex structure influences ____________ growth because usually young individuals reproduce and older individuals die.

9. Under ideal conditions, populations of most species can grow at ____________ rates.

10. Population ____________ is the number of individuals in a population.

11. The formula for population ____________ is r = (b + i) - (d + e).

12. Species that live in ____________ environments are likely to r-selected.

13. Dispersal refers to offspring moving ____________ from their parents.

14. A ____________ is a group of organisms of the same species that live in the same area.

Lesson 12.2: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Compare and contrast exponential and logistic growth.

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