Download SA Ecology

1. The populations of wolves and moose in Isle Royale National Park, Michigan
have been observed to undergo cycles of alternating peaks.
Explain how the moose population is likely held in check by predation by wolves.
The populations of wolves and moose in Isle Royale National Park, Michigan have
been observed to undergo cycles of alternating peaks. The graph depicts the longterm study of the predator-prey relationship of the moose and wolves in Isle
Royale National Park. Use the data to explain why the two populations have never
reached the expected equilibrium
Answer Key:
Rubric:
2 pts Two key elements
1 pt One key element
0 pts Other
Key Elements:
A: The moose population is directly influenced by the amount of forage. The less
forage, the fewer moose that survive. Wolves tend to seek out the weak, old, and
sickly moose, leaving the healthy to reproduce.
B: Both populations are affected by health issues such as disease and parasites.
C: Any other plausible reasons for an increase in one population and a decrease in
the other.
Keywords:
prey, predation, forage, food, chain, web, old, sickly, reproduce, disease, parasite,
increase, decrease
OR
Other equivalent reason.
Keywords:
reproductive, rate, outcompete, compete, competition, population, attach, anchor,
chain, boat, ship
B: An increased supply of prey, i.e., river fish, is likely to lead to an increase in the
snake population.
OR
Other equivalent statement.
Keywords:
habitat, population, prey, predator, prolong, inundation, flood, plain, fish, increase,
more, food
2. The energy pyramid of a wetland food chain is shown here.
If the grasshoppers in a certain area receive 500 million joules of chemical energy
from the plants they eat in one day, what is a reasonable estimate of the amount of
chemical energy the frogs in the same area will get from their food? Justify your
answer.
Ecology
(BIO.B.4.2.1) Energy Flow
Answer Key:
Rubric:
2 pts: Two key elements are present.
1 pt: One key element is present.
0 pts: No key elements are present.
Key elements:
A: According to the 10% rule each trophic level in a food chain typically receives
roughly 10% of the chemical energy that the trophic level immediately below it
receives in the same time-period.
OR
Other statement explaining the relation between productivity rates at successive
levels of a food chain.
B: Frogs are one trophic level above the grasshoppers in the pyramid, so by the
10% rule, they receive about 10% of 500 million joules, or 50 million joules of
chemical energy
OR
Other reasonable estimate.
Scoring note:
As the so-called 10% rule is really only an order-of-magnitude estimate, students
should be given credit for any other estimate of the right order of magnitude
Keywords:
10%, ten, percent, rule, trophic, level, energy, available, higher, lower
3. A food-chain of a rice field ecosystem is shown.
Snake
↑
Field rat
↑
Rice Plant
Field rats feed on rice grains.
How would the snake population of a rice field likely be affected in the year
following a serious drought? Explain your answer.
Answer Key:
Rubric:
2 pts: Two key elements are present.
1 pt: One key element is present.
0 pts: No key elements are present.
Key elements:
A: A drought would result in a low production of grain, leading to a decrease in the
rat population.
OR
Other equivalent statement.
B: As field rats are the snakes' prey, the snake population would decrease in
response to the lower availability of food.
OR
Other equivalent statement.
Keywords:
prey, population, drought, decrease, available, food
4. A few hundred red deer were introduced, in 1998, into a prairie ecosystem
where they faced no natural predators. The graph shows the subsequent variation
of the deer population in a certain area of the prairie.
Explain, using the concept of carrying capacity, the observed variation of the deer
population over time.
Answer Key:
Rubric:
2 pts: Two key elements are present.
1 pt: One key element is present.
0 pts: No key elements are present.
Key elements:
A: The deer had no natural predators, and being herbivorous, had readily available
food resources. Therefore, as long as the deer population was small, it grew
rapidly.
OR
Other equivalent statement.
B: The amount of food available within a given area could support only a certain
maximum population indefinitely. After the population exceeded this carrying
capacity, the population fell slightly and stabilized itself at a sustainable level.
OR
Other equivalent explanation.
Keywords:
carrying capacity , maximum , food, population, stabilized
5. In the early 1900s hunters almost caused sea otters to become extinct on the Pacific coast
of the United States. What happened when the sea otters were removed from this food web?
Ecology
(BIO.B.4.2.2) Biotic Interactions
Answer Key:
The removal of a species will cause a cascade effect. Without the otters to control
the urchin population, the urchins increase exponentially. This will cause a massive
decrease in or extinction of the kelp population. Without any food to eat, the would
become extinct as well. Because the kelp beds are the home of many other species,
these other species can become extinct. Also, with the sea otters gone, the killer
whales will be forced to feed only on the harbor seal. This will cause the harbor
seal populations to diminish and their food sources to flourish.
Keywords:
cascade effect, decrease, increase, food, kelp, killer whales, harbor seal