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Deer: Predation or Starvation How to Best Manage the Population?

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Deer: Predation or Starvation How to Best Manage the Population? Introduction: In 1970 the deer population of an island forest reserve about 518 square kilometers in ... – PowerPoint PPT presentation

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Title: Deer: Predation or Starvation How to Best Manage the Population?


1
Deer Predation or StarvationHow to Best
Manage the Population?
2
Introduction
  • In 1970 the deer population of an island forest
    reserve about 518 square kilometers in size was
    about 2000 animals. Although the island had
    excellent vegetation for feeding, the food supply
    obviously had limits. Thus the forest management
    personnel feared that overgrazing might lead to
    mass starvation.

3
  • Since the area was too remote for hunters, the
  • wildlife service decided to bring in natural
    predators
  • to control the deer population. It was hoped that
  • natural predation would keep the deer population
  • from becoming too large and also increase the
    deer
  • quality (or health), as predators often eliminate
    the
  • weaker members of the herd. In 1971, ten wolves
  • were flown into the island.
  • (The addition of living organisms, like the
    wolves, to an ecosystem is called
    BIO-AUG-MEN-TA-TION.)

4
The results of the wolf introduction
follow. Discuss what you think you will see
5
Year Wolf Population Deer Population Deer Offspring Predation Starvation
1971 10 2000 800 400 100
1972 12 2300 920 480 240
1973 16 2500 1000 640 500
1974 22 2360 944 880 180
1975 28 2224 996 1120 260
1976 24 2094 836 960 2
1977 21 1968 788 840 0
1978 18 1916 766 720 0
1979 19 1952 780 760 0
1980 19 1972 790 760 0
6
  • Task 1 Graph the wolf and deer populations,
    using a different color for each population.

7
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8
Year Wolf Population Deer Population Deer Offspring Predation Starvation
1971 10 2000 800 400 100
1972 12 2300 920 480 240
1973 16 2500 1000 640 500
1974 22 2360 944 880 180
1975 28 2224 996 1120 260
1976 24 2094 836 960 2
1977 21 1968 788 840 0
1978 18 1916 766 720 0
1979 19 1952 780 760 0
1980 19 1972 790 760 0
9
Task 2 Draw a line graph which compares the
number of individuals in the deer population
versus their age. This is called an Age
Structure graph
10
Draw a line graph which compares the number of
individuals in the deer population versus their
age. Age Number of deer in Age Number of
deer in the population the population 0-1
860 5-6 88 1-2 345 6-7 68 2-3 262
7-8 56 3-4 168 8-9 42 4-5 105 9-10
6 Total 2000
11
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12
Questions
  • Describe what happened to the deer and wolf
    populations between 1971 and 1980
  • What do you think would have happened to the deer
    on the island had wolves NOT been introduced?
  • Would it have been better if more wolves had been
    introduced in 1971? Why or why not?
  • In which year was deer starvation greatest? Why
    ?
  • Does the number of wolves limit or control the
    number of deer in this ecosystem? Explain

13
6. How does the size of the deer population
influence the number of wolves on the island?
If no hunting is allowed, what natural
mechanisms will control the wolf population? 7.
Which stages in the life of the deer have the
highest mortality? Suggest environmental factors
which might make this so. 8 How could
knowledge of an age structure graph be
helpful in determining the management of herd
populations?
14
  • 9. Most biology textbooks describe that
    predators and prey exist in a balance. This
    balance of nature" hypothesis has been
    criticized by some scientists because it suggests
    a relationship between predators and prey that is
    good and necessary. Opponents of this hypothesis
    propose the following questions
  • Why is death by predators more natural or
    "right" than death by starvation?
  • How does one determine when an ecosystem is in
    "balance?
  • Do predators really kill only the old and sick?
  • What evidence is there for this statement?
  • What is your opinion of the balance of
    nature hypothesis? Would the
  • deer on the island be better off, worse
    off, or about the same without the
  • wolves? Defend your position.
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