EXAM 2 Sample Questions/Answers (No question from Ch 13 or 15; not on this exam)
CH 12 Family, Society, and Evolution
Scrub jays nest in groups with only a few breeding adults. Other members of the group
sometimes help to rear the offspring of the breeding pairs.
1. Make a labeled graph predicting how the probability of helping is linked to the
coefficient of relatedness between breeders and non-breeders.
2. How do you explain your prediction?
3. What type of selection is possible with this social structure?
4. Upon what important ability does this social structure depend?
Answer:
1. Greater probability of helping (vertical axis) with greater coefficient of relatedness
(horizontal axis). Line with positive slope.
2. Non-breeders are willing to help breeders because it increases their inclusive fitness.
Individuals are more likely to help individuals that are more closely related to them
because they share more genes in common and more of the non-breeders’ genes will be
passed to the next generation via the breeders.
3. Kin selection
4. Ability of an individual to determine its degree of relatedness to other individuals in
the social group.
CH 13 + CH 15: There will be no question derived from this lecture and chapters.
CH 14 (see below)
CH 17 Predation and Herbivory
1. Contrast the main difference in these types of plant chemical defenses:
A. Constitutive
B. Inducible
2. Relative to a constitutive defense, how does an inducible defense benefit the plant?
What is one potential negative aspect of an inducible defense?
3. Showshoe hares eat young shoots of trees in winter. Ecologists found that trees with a
high % shoots eaten in Year 1 had a high concentration of chemical defense in Year 2.
The question is: Did herbivory in Yr 1 CAUSE the high defense in yr 2?
A. Develop an “if…then” that addresses this observation.
B. Complete a figure to illustrate the expected results that would support your
hypothesis. Label axes
C. What is a key assumption underlying your hypothesis?
Answer:
1. Constitutive: a defense that is always present
Inducible: a defense that is produced in response to herbivory
2. Inducible defenses save energy and resources by making them only if needed.
By contrast, constitutive defenses bring a fixed cost in energy and resources,
even though they may never been needed if there is no herbivory.
3. A If…,herbivory by hares in yr 1 causes (induces) the high defense in yr 2,
then…trees with herbivory in yr 1 will have 1) greater amount of defense and 2) less
herbivory in yr 2 than caged trees with no herbivory in yr 2.
3B. Figure horizontal axis: two treatments (with herb. in yr 1 and without herb. in yr 1);
vertical axis (left side: amount of defense in yr 2; right side: level of herbivory in yr 2.
RESULTS: 4 bars that illustrate exactly what is in the prediction.
3C. The defense makes the shoot unpalatable (or has a negative effect) to hares.
OR The defense is primarily for hares.
CH 18 Dynamics of Predation
Birds, especially warblers, are primary predators of the insect spruce budworm, an
invading pest of boreal forests. The ability of the predators to control these prey during a
huge outbreak of the budworm was monitored.
1. Warblers showed a Type II functional response to increasing prey density. Illustrate
this response in Fig. A. Explain the shape of the predator’s response.
2. Warblers also show a numerical response to increasing prey density. Illustrate this
response in Fig. B.
3. Which type of response, functional or numerical, is made by individual warblers?
4. Fig. C shows the population response of the warblers to increasing prey density. Were
the predators able to control these prey? Explain.
Answer:
See lecture Power point slides; pg 4 (if 9 slides/pg) in upper right.
1. Fig. A. The individual predator eats more prey as prey density increases, but
eventually its stomach fills, i.e. predator satiation occurs, and the function therefore slows
at high prey density.
2. Fig. B.
3. Functional = individual response
4. No, while the mortality due to predation increased as density increased at low density
ranges, it dropped dramatically at high densities. This indicates that the outbreak was far
greater than the warbler population could control, despite having both positive functional
and numerical responses.
CH 19 Competition
The figure below illustrates the distribution of two species of buttercups along a transect
across ridge (high land) and furrow (low valley) grassland.
1. In one sentence summarize the results.
2. Provide two alternative hypotheses (If…then) for the observed pattern. (State a
general, not specific hypothesis such as light or moisture).
3. Draw or describe one complete experiment that would test both hypotheses.
4. What specific results from the experiment would provide support for your hypothesis
1 above?
Answer:
1. The two species each have their peak abundance in either furrow or ridge.
OR Sp 1 is largely on the ridge and Sp 2 is largely on the furrow.
2. A If …the distribution of the two species is caused by tolerance of environmental
(abiotic) conditions,
B. If…the distribution of the two species is caused by (symmetric) competition,
3. Grow each species alone and with the other species in both ridge and furrow sites.
4. Environmental tolerance Hypothesis:
When grown alone, sp 1 grows better on F than R; sp 2 grows better on R than F.
OR Each species grows better than the other species on its home site.
OR Competition Hypothesis:
When grown together:
Sp 1 grows better than sp 2 on F, but sp 1 grows worse than sp 2 on R.
Sp 2 grows better than sp 1 on R, but sp 2 grows worse than sp 1 on F.
CH 20 Coevolution + Mutualism
Acacia trees have a mutualistic relationship with ants.
1. Develop an “if…then…” relating to the benefit of the mutualism to the plant.
2. Does the existence of the mutually beneficial traits in this mutualism confirm this
relationship as an example of coevolution? Explain, including what is the best evidence
of coevolution.
3. Not all species of acacia form a mutualism with ants. In a setting where herbivore
pressure is low, why might the mutualism not have arisen?
4. In some areas where herbivore pressure is high, the mutualism with ants has not
arisen. Predict two
alternative anti-herbivore defenses these acacias may be using.
Answer:
1. If…ants benefit the plant by lowering herbivory,
then…plants with ants will have lower leaf loss than plants with ants excluded.
2. No, it is possible that what appear to be coevolved traits may have been present before
the mutualism developed (preadaptations). Also adaptations of mutualists may arise from
diffuse coevolution. Determining coevolutionary origins of mutualisms is difficult
because evidence of earlier, intermediate steps is lacking. The best evidence comes from
phylogenetic reconstruction of the evolutionary history of tris in the presumed coevoled
groups of organisms.
3. Adaptations to house and feed ants are costly in terms and energy and resources.
Plants use those resources for growth, survival, and reproduction. Costly adaptations
should not arise in he absence of any benefit.
OR the random mutations may have have arisen.
4. A. Toxic chemicals (secondary chemicals)
B. Low nutrition in vulnerable parts
C. Tough leaves
CH 21 + 23 Species Abundance + Species Diversity (Richness)
A 100-yr experiment tested the effect of fertilizer on species diversity (H’) in a grassland.
RESULTS: H’ of unfertilized remained steady.
H’ of fertilized decreases through time.
1. Summarize the major result of the study.
SKIP 2 + 3; we didn’t cover this in lecture.
2. What 2 components of a community does the Shannon-Wiener Index (H’)
incorporate?
3. What combination of these components yields the greatest value of H’?
4. Explain the results in terms of competition and niche theory.
Do the results support the hypothesis that the superior competitor can exist at lower
resource levels than its competitors? Explain.
Answer:
1. See above (I gave the results instead of the figure).
2. Skip
3. Skip
4. At low nutrient availability (control), potentially superior species are not growing
large enough to exclude other species. Hence this treatment has high species richness.
Furthermore, species are probably evenly represented as no species dominates. Niche
overlap may be minor and of little consequence. In contrast, at high nutrient availability,
plants grow large. Niche overlap matters. Superior competitors exclude some species so
species richness drops.
No, you can’t tell without experimentation. This may or may not be the mechanism that
is operating.
CH 14 Population Growth + Regulation
Formulae that will be provided:
 = Nt+1 / Nt
Nt = t No
Nt = No ert`
dN/dt = rN
dN/dt = rN (K – N)/K
1. Review Homework 9. Population Growth Problem Set 1. Pay particular attention to
identifying the formulae used for each question.
2. Then for each formula above, what type of general question does it answer about
population growth and regulation?
3. To what type of math model does each formula apply (e.g. geometric growth,
exponential growth, logistic growth)?
In addition, review life tables and their use in predicting future population growth and
changes in age distributions…=
4. Review Questions 2 + 4 of Problem Set 2 for Population Growth (pink sheet we did in
lecture)
Question 2:
a. How to transfer information from a text description about age-specific birth rate
and survival rate into a life table.
b. What do lx and mx refer to and how is lx calculated?
Question 4:
Review the table and answers associated with the table.