Your Name:
1
ES 100
Midterm Exam
Fall 2003
True or False: If false, briefly state why.
1. (5) Maximum sustainable yield management is designed to keep a population at its carrying
capacity.
False. MSY management is designed to keep a population at the point where the largest
harvest can be taken that does not reduce the population. This translates into harvesting
net population growth above the current population. This can only occur at a population
population below carrying capacity, where there will be no net growth (that is the
definition of carrying capacity).
2. (5) The science of ecology is unique in that it is based entirely on integrationist, rather than
reductionistic approaches to analyzing nature.
False. Ecology incorporates both integrationist and reductionist approaches.
3. (5) The hypolimnion of a lake is the deep cold layer.
True
4. (5) Small islands typically lack top predators that are found on the mainland because the
predators can’t make it to the islands.
False. Small islands typically don’t have to total productivity necessary to support as many
trophic levels as a large island. Mainland predators don’t necessarily have a harder time
getting to a small island than the herbivores or lower level predators do.
5. (5) Trophic pyramids in the ocean are often “inverted” in terms of biomass but not in terms of
productivity.
True.
6. (10) What do you think the effect of increasing temperature and increasing fresh water inputs
in the North Atlantic would be on marine mammal populations in the North Pacific Ocean?
Why?
These conditions could lead to a shut down in the Great Ocean Conveyor, the circulation of
water that “starts” when cold salty water sinks in the North Atlantic, flows south to the
Southern Ocean around Antarctica, then north into the Indian and North Pacific Oceans
where it rises to the surface and back toward the Atlantic. If the Conveyor shut down, it
would stop the upwelling of nutrient-rich deep water in the North Pacific, potentially
drastically reducing the productivity of ecosystems in the area, including reducing
productivity of marine mammals.
Your Name:
2
7. (10) You are studying an animal in which each female bears a single litter of 1-2 young and
can bear young any time during the year. The population dynamics of this species is likely to be:
stable, show a smooth, regular cycle, chaotic? Why?
Most likely stable. This looks like a K-selected organism. The population is likely to stay
near carrying capacity. Any growth will be slow and well distributed across the year. There
won’t be any huge population booms to cause carrying capacity over-shoots that are
followed by population crashes.
This looks like an r-selected type growth strategy: high
reproductive output per individual but a low rate of
survival. Such organisms are typically short-lived (think
insects or mice). Thus, the units are probably most likely
weeks (roughly a 1-year lifespan) but could be months.
Almost certainly NOT years.
1.0
0.8
Survivorship
8. (10) Consider the survivorship curve for a land animal at
right. Are the time units on the x-axis more likely to be weeks,
months, or years? Why?
0.6
0.4
0.2
0.0
0
10
20
30
40
50
Time
9. (10) A simplified food web of the Aleutian Islands is shown in the figure at right. Consider the
following pieces of information:
I. Over the last decade, the sea water temperatures have warmed slightly.
II. The only group of organisms this affected directly
Killer Whales
is the plankton, but they are quite sensitive and
their productivity has been greatly reduced.
III. Killer whales prefer to eat seals.
Seals
Sea
otters
Seabirds
What would you predict would be the state of the fish
that live in the kelp forest? Why?
Smelt
fishes
Urchins
Plankton
Kelp
Plankton would decrease and so, therefore would all
organisms up through seals. That would lead Killer whales to shift to eating sea otters as a
major food source. Sea otters would decrease, allowing urchins to increase. That would
reduce kelp biomass, reducing habitat for fish that live in the kelp forest. Thus, a reduction
in plankton would likely reduce the populations of fish that live in the kelp forest.
Other
fish
(live in
kelp forest)
Your Name:
3
10. (15) You are studying a farm that raises organic soy beans and chickens. The chickens are
fed the husks from the soy beans that are shipped off to market. The chicken manure is used as
fertilizer for the soy beans. The farmer doesn’t use any fertilizer from off the farm.
The farm ships off 1000 Kg of soy beans per hectare. The N content of that amount of soy bean
is 25 Kg Nitrogen (N).
The farm produces 100 chickens per hectare. Each chicken weighs about 1 Kg processed and
contains 50 g N.
The farmer applies about 250 Kg/hectare of chicken manure to the fields. Chicken manure
contains about 100 g N per Kg manure.
A. (10) If the soils are to remain in balance, neither gaining nor losing N over time, how much N
must be entering the system via N fixation by the soy beans or from atmospheric deposition.
N in chickens = 100 * 50 g = 5000 g = 5 Kg.
Total N export = 25 Kg N as soybeans + 5 Kg N as chicken = 30 Kg N export.
Thus, 30 Kg must be supplied from outside the system.
The chicken manure is completely irrelevant- it is merely N being recycled within the
system.
B. (5) The farmer insists that he is farming fully sustainably. Is he? Why or why not?
No. While the N may be resupplied via deposition or N-fixation, other elements are not
likely to be resupplied this way. Phosphorous is almost certainly being “mined” out of the
soil.
11. (10). You are studying a kelp reef ecosystem off the coast of California. In this system you
find at least 2 species that feed exclusively on kelp. How can this be? Why hasn’t one
competitively excluded the others? Provide two specific mechanisms.
They have most likely partitioned the kelp niche. There are multiple ways this could be
done.
Depth in the water column: e.g. shallow vs. deep.
Part of the kelp: e.g. blades vs. stems.
Time of day: e.g. day vs. night
Time of year: e.g. winter vs. summer
Alternatively, they could be competing directly and competitive exclusion simply hasn’t
happened yet.