Deer Predation VS Starvation

Deer - Predation or Starvation 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. 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 results of this program are shown in the following table. The Population Change is the number of deer born minus the number of deer that died during that year. Fill out the last column for each year (the first has been calculated for you). Year Wolf Population Deer Population Deer Offspring Predation Starvation Deer Population Change 1971 10 2,000 800 400 100 +300 1972 12 2,300 920 480 240 +200 1973 16 2,500 1,000 640 500 -140 1974 22 2.360 924 880 180 -116 1975 28 2,224 996 1,120 26 -150 1976 24 2,094 836 960 2 -126 1977 21 1,968 788 840 0 -52 1978 18 1,916 756 720 0 +46 1979 19 1,952 780 760 0 +20 1980 19 1,972 790 760 0 +30 1. Graph the deer and wolf populations on the graph below. Use one color to show deer populations and another color to show wolf populations. 1 Analysis 1. Describe what happened to the deer and wolf populations between 1971 and 1980. The deer and wolf populations both increased until they reached a maximum and then began to decrease until they reached a minimum. Once they reached a minimum, they began to increase at a smaller rate until they leveled off and maintained their population. The rising and falling of the populations happened at different times, but was first seen in the deer population 2. What do you think would have happened to the deer on the island had wolves NOT been introduced? Had the wolves not been introduced to the island, there is a good change that the deer population would have ultimately died out because there would not have been enough food to support all of the deer present on the island. 3. Most biology textbooks describe that predators and prey exist in a balance. Some scientists have criticized this “balance of nature” hypothesis because it suggests a relationship between predators and prey that is good and necessary. Opponents of this hypothesis propose the following questions (don’t answer these, just think about them): Why is death by predators more natural or "right" then death by starvation? How does one determine when an ecosystem is in "balance"? Do predators really kill only the old and sick prey? What evidence is there for this statement? 2 Consider both sides of the argument. 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. Guiding Question: Would the deer on the island be better off, worse off, or about the same without the wolves? Claim: A balanced ecosystem is one in which the birth and death rates are roughly equal and that the population is at such a level that the ecosystem can support that number over a very long period of time. Starvation is less favorable than predation because if deer are starving then that means the ecosystem is out of balance and cannot produce enough food to support all of the deer. If there are too many deer in an ecosystem, they could consume all of the food and if all of the food disappears, then ALL of the deer will perish and could lead to extinction. While predators do kill deer, they only kill and eat what they need to survive. Deer loss by predation is usually much lower than death by starvation and doesn't result in the complete loss of all deer or the complete destruction of the ecosystem. Evidence: Justification: 3