Your code: KEY
Page 1 of 12
THIS KEY GIVES ONE SET OF POSSIBLE ANSWER. OTHER OPTIONS WERE POSSIBLE AND MAY
HAVE RECEIVED CREDIT.
(N=65 STUDENTS TOOK EXAM )
GENERAL ECOLOGY (PCB 4043)
• Write your code on all the pages
• Make sure that all pages are attached.
• You may not use calculators, cell phones, brain chips, or other electronic aids. The math
needed to solve a problem should be relatively simple. If you can't do the math, just
show what needs to be calculated (e.g., "answer = .5 x .3")
• If you get hung up on a problem, skip it; return to it after you’ve answered the “easy”
PAGE PPOSINBSLE SCORE
1 2 _____
2 6 _____
3 8 _____
4 8 _____
5 10 _____
6 10 _____
7 6 _____
8 11 _____
9 10 _____
10 11 _____
11 8 _____
12 10 _____
TOTAL 100 _____
1-1. ( 2 points for either answer) Are you interested in being an undergraduate TA for this
course next year? ( YES, NO ) Either answer accepted Your code: KEY
Page 2 of 12
2-1. A student doing an independent project (Zoo 4905) monitored Daphnia growth in a
lake, and based on their performance was able to describe how the per capita growth
rate varied as a function of density. Her data are shown below.
dN/Ndt-0.2 0 2 4 6 8 10 12 14
Per Capita GrowDaphnia Density (no. / 10 ml)
a) (4 points) Given enough time, to what density will the population converge if
initiated at the following densities:
N 0= 1 0
N 0= 3 11
N = 7 11
N 0= 14 11
b) (2 points) Give a biologically plausible explanation for this hump-shaped function
(your answer must be sufficiently complete to explain both the rise and fall of
• Initial increase: Allee affect due to Type II functional response (e.g.,
due to handling time) or social facilitation of reproduction or
• Eventual decrease: Intraspecific competition, aggregation by
predator, increased incidence of disease Your code: K EY
Page 3 of 12
3-1. (2 points) Dr. I.M. Green monitored a plant population’s density through time (note
the logarithmic scale):
01 234567 89 01
Over which time period does the plant population exhibit the greatest per capita
growth rate (circle the correct option)?
i. 0-3 yrs
ii. 3-6 yrs
iii. 7-10 yrs
iv. The answer can’t be obtained from the data available
3-2. The dynamics of three species can be described using the following equations (where
N is density, in no./m 2):
dN 1N d1 = +1.0 – 0.1N – 1.1N 2
dN 2/N 2t = +0.6 – 0.2N –10.2N – 021N 3
dN 3N d3 = –0.1 + 0.1N 2
For each of the following, choose (i.e., circle) the best option from the those available
a) (1 point) Species 1 and 2 are:
( competitors; predator and prey; mutualists, do not interact directly )
b) (1 point) Species 1 and 3:
( competitors; predator and prey; mutualists, do not interact directly )
c) (4 points) In the absence of Species 3, Species 1 and 2 will:
( both persist; only species 1 will persist; only species 2 will persist;
neither will persist; there is not enough information provided )
hint: for c) apply the concept of invisibility. Your code: KEY
Page 4 of 12
4-1. The following life cycle diagram is based upon a time interval of one year.
0.3 0.1 0.5
Eggs 0.6 Small 0.5 Medium 0.3 Large 0.1 Adults
Juveniles Juveniles Juveniles
a. (3 points) What proportion of individuals in each life stage survive from one year
to the next?
b. (2 points) If there were 100 individuals of each stage on April 1, 2010, how many
large juveniles should there be one year later (on April 1, 2011)?
LJareniles 40 = (100*0.3 + 100*0.1)
c. (1 point) Given enough time (and assuming the transition values remain
constant), this population will grow… (pick the best option):
( tangentially; density-dependently; exponentially; logistically )
d. (2 points) In the real-world, provide two reasons why the transitions could change
(i.e., not remain constant).
• Change in the environment (e.g., global warming, change in predator
density, invasion of a competitor, etc.) Your code: KEY
Page 5 of 12
5-1. ( 3 points) You observe that a species of butterfly very common on the Florida
peninsula is absent from islands in the Florida Keys. Provide three hypotheses that
might explain the absence of the butterfly from the islands.
• Unable to disperse across water (too far)
• Abiotic environment is unsuitable
• Lack of suitable host plant for oviposition by females
• Lack of suitable host plant for surivival of larvae (caterpillars)
• Excessive predation
• Intense competition
• Presence of pathogens
5-2. ( 3 points) Two species of lizards that live in oak hammocks around Gainesville.
Provide at least three hypotheses that might explain how the lizards are able to coexist
in hammock environments.
• The don’t interact
• Resource partitioning (they eat different food; occur in different
• Disturbance (e.g., hurricanes are frequent enough to prevent competitive
• Habitat heterogeneity (related to resource partitioning)
• Trade-off between colonizing ability and competitive ability.
• Better competitors are more vulnerable to disturbances.
• Better competitors are more vulnerable to predators (or parasites).
• Neutral theory: there is no “best competitor”; instead species are equivalent
and there is a slow ‘walk’ to extinction. Extinction is balanced by
speciation. [this really isn’t coexistence, but we’ll give credit for this.]
5-3. ( 2 points) In class we’ve seen that increasing species richness can increase
primary production. We’ve also discussed coexistence of competitors. Combine
these concepts to explain why increased species richness might increase primary
Coexistence is facilitated through resource partitioning. As a result of resource
partitioning, two (or more) species will use the available resources more
“effectively”: e.g., consider two plant species that partitioning nutrients – one is
limited by N and one by P; their combined use of N and P (and their productivity)
will be greater than either species alone.
5-4. ( 2 points) You work for the USDA and you have been charged with finding a
biocontrol agent that might stem the outbreak of pine beetles. Explain at least two
key traits of a biocontrol agent that you’d look for:
• High attack rate (ability to find and kill prey at high rates even at low
• High conversion efficiency (i.e., ability to produce new predators with few
prey: e.g., parasitoids).
• Not harm other species
• Low mortality rate. Your code: K EY
Page 6 of 12
a) (1 point) Exploitative competition
A jointly negative interaction between two species that arises through a shared,
depletable, and limiting resource.
b) (1 point) Interference competition
A jointly negative interaction between two species arises through direct agonistic
interactions (e.g., territoriality).
c) (1 point) Functional response
A functional response describes the relationship between the feeding rate of a
predator and the density of its prey.
d) (1 point) Indirect effect
An IE arises when one species affects another through its affect on the density of
an intermediate species (e.g., if AÆBÆC, then A has an indirect effect on C by
affecting the density of B (which in turn affects C’s dynamics).
e) (1 point) Higher order interaction
An HOI occurs when the density of one species affects the strength (or sign) of the
interaction between two directly interacting species.
6-2. (2 points). Provide one explanation for why decomposition of soil organic matter is
slow in the arctic.
• Low temperature limits microbial activity
• Low nitrogen availability limits microbial activity
6-3. ( 3 points). List three reasons why the marsh cordgrass, Spartina alterniflora, is
considered a pioneer species in the development of eastern U.S. salt marshes.
• They are highly tolerant of anoxic soils and high salinity
• Their aboveground structure slows water movement, which causes
sedimentation and marsh accretion
• Their large root systems stabilize the substrate and prevent erosion.
• Rapid clonal expansion through aggressive rhizome growth allows for the
expansion of marsh areas. Your code: KEY
Page 7 of 12
7-1. ( 6 points). You work for the National Marine Fisheries Service. A new species of
sea life has been discovered and it makes awesome sushi. You have been charged
with coming up with a management plan to ensure that this species can be harvested
sustainably (i.e., it will be harvested, but you need to find a way to ensure its
continued persistence and availability to fishers). You consider a range of options:
• Fixed harvest (you define a fixed number of critters to be harvested)
• Fixed effort (you only allow a fixed number of permits)
• Spatial reserves (you restrict fishing to certain regions)
Which approach (or combination of approaches) do you recommend and why (feel
free to use words, equations or figures to explain your approach)?
A fixed harvest approach (of which the unstable “maximum” sustained yield is a
special case) is unstable. Even if a stable equilibrium is possible (at exploitation
rates below MSY) the system is sensitive to uncertainty in stock size and production.
Uncertainty can easily give rise to overharvesting and depletion of stocks.
Fixed effort is generally better (it gives rise to a stable equilibrium) but is still
problematic if uncertaintly is very large. It’s also sensitive to fisher behavior which
can modify the expected harvesting-stock size relationship to generate unstable
equilibria (much like with the fixed harvest scenario).
Marine reserves are thought to be best because they protecet a fixed (and known)
fraction of the population (at least at a given time; movement could reduce this
effectiveness). As a result marine reserves are less likely to generate unstable
overexploitation in the face of environmenta