BCOR 102 Exam 3
Name:
1. In the Lotka-Volterra competition equation dN1/dt = rN1 ((K1-N1- N2)/K1).
What is the meaning of the terms:
a. dN1/dt
b. K1
c. 
2. Here are two possible state space graphs for two competitor species, with zero
growth isoclines for species 1 (solid) and species 2 (dashed). Starting at positions
x, y, and z draw the arrows that show the projected population dynamics.
Sp 2
isocline
N2
x
z
Sp 1
isocline
y
N1
x
N2
z
Sp 2
isocline
N1
y
Sp 1
isocline
3. The basic predator-prey model uses the following system of equations for
predators and victims:
dV/dt = rV – VP
dP/dt = VP – qP
Assume you have measured the following parameters:
the intrinsic growth rate (r) of the victim population is 0.30;
the intrinsic death rate of the predator is q=0.20;
= 0.005
 = 0.008

Number of Predators
a. Draw the zero
growth
100
isoclines for
the predator
80
and victim (be
sure to label
60
which is
which!).
i.
40
b. If the
abundance of
20
the predator
and victim
0
populations
start at the
0
50
100 150 200
point shown on
Number of Victims
the graph, draw
an arrow
showing the initial changes in the population sizes.
4. The marginal value theorem (see graph) is used to predict the optimal time a
forager should spend in a patch.
a. Label the axes.
b. Now imagine that it is a
good year and the average
B density of patches
increases. How does that
change the graph?
c. Should the forager spend
more or less time in a
patch? Why
A
C
5. The MacArthur-Wilson theory of island biogeography is often depicted in
graphical form, like this:
a. Label the axes
b. Label the immigration and extinction curve
c. Now modify the immigration curve to that of a more distant island?
d. How does that change the equilibrium number of species?
6. Bluegill sunfish have a choice of several possible food items, with the following
energy values and search times. Which items should be included in their diet and
which should be excluded if the bluegills are foraging optimally?
Prey
Type
Search
Time
si (sec)
Handling
Time
hi, (sec)
Energy
per Prey
Ei (kJ)
Profitability
Ei/hi
A
30
10
8
0.8
Value of
continued
searching
Ei/(hi+si)
0.2
B
10
2
2
1
0.166
C
4
4
2
0.5
0.25
D
10
10
12
1.2
0.6
Include
in
Diet?
(Y/N)
7.
In New England forests, tree species compete primarily for light. Imagine that an
ecologist made these measurements on the trees.
a. Which column corresponds to R*?
b. Which species will be the competitive dominant(s)?
Species
Minimum Light
for growth (umol)
Beech
2
Hemlock
3
Sugar Maple 7
Red Maple
15
Red Oak
20
Yellow Birch 6
White Birch 45
Maximum
growth rate (mm/yr)
5
3
7
12
15
8
18
Mortality rate
(trees/yr)
0.001
0.003
0.001
0.025
0.022
0.018
0.033
8. Lawns are near monocultures, in part because grass is a good competitor. It will
outcompete most weeds such as dandelions etc. Nevertheless, any homeowner
will tell you that dandelions and other weeds persist in their lawns. Using the
principles we have learned in class, what might allow those weeds to persist in
face of competition from a superior competitor (grass)?
9. This figure shows the pattern of food use for three species that have somewhat
overlapping diet requiements. For each pair of species, estimate the approximate
value of the competiton coefficient (): (circle one)
Freq
1
2
3
Resouce Gradient
1 vs 2
    
2 vs 3
    
1 vs 3
    
10. Tadpoles of wood frogs and spring peepers compete for food in a pond. Assume
that wood frogs are the less efficient forager: From the perspective of peepers,
each wood frog reduces the food available to peepers as much as 0.75 spring
peepers. From the perspective of wood frogs, each peeper is equivalent to 0.90
wood frogs. Finally, assume that both have equal carrying capacitites (K=100).
Can these species coexist?
11. What is the evolutionary explanation for why males of many bird species
(peacocks, mallards, cardinals, etc.) are more brightly colored than the females?
(i.e. why is it always the male?)
b. A few species have the opposite pattern. E.g. female jacanas and
phalaropes are more brightly colored than the males. What would you
predict about the mating behavior and patterns of parental care in those
two species?
12. Does the “good genes” model of sexual selection require conscious choice on the
part of females? Why or why not?
13. What is an “Evolutionary Stable Strategy” (ESS)?
EXTRAS
Draw a state-space graph (N1 vs N2) showing a situation where the two competitors
can coexist. Label the axes, isoclines, K1 and K2.
Bonus: For that same scenario and same parameters, draw a graph of N1
vs time, starting with K1 of species 1 and 1 of species 2.
Two spp in same habitat. One is a generalist . Can’t be any difference in prey
abundance (same opportunities). If foraging optimally, what difference might cause
one to be a generalist?
Competition
give Ks, allpha and beta: can these spp coexist?
Draw state space isoclines for story problem
Removal expts
Predation
why cycles?
Niche Evol
something about anolis?
Distribuition of food use for two sizes of anoles. Overlap. Abundance of food.
Direction of selection on the small one?????
Islands
Succession
Draw a loop diagram for the "faciliation" model (3 class: annual, perennial, trees).
Make up a matrix that corresponds to your loop diagram of succession.
Games: what is an ESS?
Foraging
Marginal value. (just like homework)
Diet choice (just like homework, but real example).
Sexual Selection
good genes vs sexy son
In a few species the males do most of the parental care. What do you expect for the
Models of female choice (such as the ‘good genes’ or ‘sexy son’ models) posit different
advantages for females the choose males with certain exaggerated traits.
Although certain phenotypes elicit the mating reponse, there is little or no evidence that
females are consciously “choosing” the mates.