Chapter 191 Populations

1
Chapter 19-1 Populations
2
Objectives

• Explain the difference between population size,
  density, and dispersion
• Describe the three main patterns of population
  dispersion
• Explain the importance of a populations age
  structure
• Contrast the three main types of survivorship
  curves

3
Populations

• Defined by place time
• Size number of individuals
• How do you find size? Count everyone?
• U.S. census
• Estimation take a small sample and extrapolate
  to a larger area
• Density How crowded?
• Individuals per unit volume

4
Density by country
5
Density by city
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Dispersion patterns
7
Population dynamics

• Birth rate number of births over a period of
  time
• Also fertility rate How many offspring each
  female has
• Developed 1/2
• Developing 5/6
• Death/mortality rate number of births over a
  period of time
• Life expectancy how long an individual is
  expected to live
• Girls live longer

8
Age structure

• Shows distribution of individuals among different
  groups.

• Explain how it is possible to conclude that the
  life expectancy of a person in a stable
  population is longer than that of a person in an
  expanding population.
• How can you tell that women have a longer life
  expectancy than men?

9
Predictions from survivorship curve

• Which countries population has the potential for
  rapid growth?
• Bottom heavy curves indicate that many young have
  been added to the youngest most reproductive
  age group.

10
Survivorship curves

• Show how many individuals survive over time
• Three different trends
• Type I youll probably live until old age
• Elephants Few young, lots of care
• Type II you have an even chance to survive no
  matter how old
• Type III youll probably die young, but if you
  survive youll live to an old age.
• Insects Many young, little care

11
Explain how populations can be the same size but
have different densities

• It depends on both the number of people and on
  space. Two populations with the same number can
  have different numbers depending on the space.

12
Explain why even distributions usually result
from social interactions between individuals

• Even distributions result when organisms attempt
  to get as far away from each other as possible.
  Carnivores have well defined territories that
  keep individuals apart.

• Stay out of my territory

13
Why might natural selection favor a high
reproductive rate in Type III organisms?

• Though many young die the surviving young are
  well adapted to the environment
• More young
• also means more
• variation

14

• Define Birth Rate
• Number of births over a period of time
• Define Death Rate
• AKA mortality Rate
• Number of deaths over a period of time

15
Explain two difficulties an ecologist might have
in counting a population of migratory birds.
Develop explain a method for estimating the
size of such a population

• Flocks are too numerous, widespread and mobile.
• Tagging individuals is one solution
• Find a bottle neck
• Count numbers passing over a period of time

• Counting a herd of zebras can be tough