Page 1 of 8
--Write your name on all the pages
--Make sure that all pages are attached.
--Any math needed to solve a problem should be relatively simple. If not, please give your answer by
showing how you would make the calculation: e.g., showing "(10+10)/4" is as good an answer as "5"
(writing down an appropriate equation and clearly defining the variables, as well as indicating their
values, if known, will also suffice).
PCB 4044 / 3063
PAGE POOSNIBLE SCORE
2 16 _____Schuyler
3 18 _____Caitlin
4 16 _____Caitlin
5 16 _____Schuyler
6 17 _____Michelle
7 17 _____Craig
8 Extra space
TOTAL 100 _____ Name: KEY
Page 2 of 8
2-1. ( 10 points) Consider the following food-chain:
bass – shiners – zooplankton – phytoplankton
You bought an undeveloped lake (it had very clear water) 10 years ago
and built your
dream house on its shores. Recently, the lake water has turned green due to
concentrations of algae (phytoplankton). List two hypotheses (involving different aspects
of the ecosystem) that can explain this increase in phytoplankton since you built your
dream house. Provide a brief explanation (1-2 sentences) of the logic underlying ea
(1) My buddies and I fished too much and reduced the density of bass, which led to a
trophic cascade: fishing of bass released shiners from predation, which led to increased
planktivory on zooplankton, which released phytoplankton from grazers.
(2) The lake has become eutrophic because I (a) fertilize my lush green lawn with a suite of
nutrients (especially nitrogen and phosphorus), and (b) my septic system might be leaking
into the lake. The increase in nutrients stimulated algal production. [Note that this
mechanism requires an incomplete numerical response of zooplankton, but you did not
have to say this to get full credit.]
2-2. (6 points) Based on the theory of island biogeography, which island in each pair, w
you expect to contain the greatest number of species (all else being equal)? Circle the
best answer from each set.
Set 1: small Large Can't be determined with
Set 2: near Far Can't be determined with
Set 3: near and large far and small Can't be determined with
available data Name: KEY
Page 3 of 8
3-1. (12 points) In the middle of the course, we noted that two competing species cannot
coexist on a single limiting resource. We subsequently discussed several ways in which
several potentially competing species could persist together. Please list and briefly
discuss (e.g., in one sentence each), three ways in which two or more competing species
can persist locally.
1. Niche partitioning (requires >1 resource); each species is limited by a different
2. Habitat heterogeneity (similar to above, but the different resources are in different
3. trade-off between colonizing ability and competitive ability.
4. Better competitors are more vulnerable to predators (or parasites).
5. Better competitors are more vulnerable to disturbances.
6. Neutral theory: there is no “best competitor”; instead species are equivalent and
there is a slow ‘walk’ to extinction. Extinction is balanced by s
3-2. (6 points) Capybara are semi-aquatic, herbivorous rodents native to South America. At
an average of 35-75 Kg, they are the largest rodents on the planet. 25
from a South Florida breeding facility, and there is concern that they may be persisting
and even reproducing in the Everglades. List six ways (1 phrase each) that Capybara
might affect native species.
1. Compete for resources (food, water, space) with native species
2. Eat native plants
3. Introduce, vector, or harbor parasites or disease that infects native sp
4. Hybridize with native species
5. Alter disturbance regime, thus changing the “rules of the game” that underlie native
6. Indirectly alter resource supply rates, thus changing etc.
7. No effect on native species? Name: KEY
Page 4 of 8
4-1. (11 points) Draw the curve of the latitudinal diversity gradient on the following
making sure to label both axes. Give three hypotheses for the origin of this gradient,
explaining each hypothesis with 1-2 sentences
(spp. #) (Spp. # per
Low 40 S 0 60 N
Low Latitude High (degrees)
1. The tropical biome has been in existence longer than higher latitude biomes, leading to
more time for species to evolve in or disperse to the tropics.
2. The tropical biome is larger in area than higher latitude biomes, leading to more space to
fit more species (e.g., island biogeography theory), more habitat heterogeneity (more
niches to fill), and larger climatically similar spaces.
3. Greater climatic stability in the tropics leads to greater specialization and more niche
partitioning than at higher latitudes, where long-term climatic variability leads to the
evolution of climatic “generalists.”
4. Speciation rates are higher in the tropics because of warmer temperatures and more
5. More diversity reinforces diversity through interspecific interactions a
nd close co-
evolutionary relationships (high predation, increased specialization).
6. Climate change over geological time has “reset” species assemblages higher latitudes
through multiple glaciations, where as the tropics have remained relatively habitable and
free from massive disturbances akin to glaciations.
4-2. (5 points) Although many tropical rainforests have high tree diversity, Jordan chose to
work in a tropical rainforest dominated by one species of tree, Dicymbe corymbosa.
(a) Explain Jordan’s hypothesis for maintenance of Dicymbe monodominance.
Dicymbe’s association with ectomycorrhizal fungi allows it to competitively exclude
other species because it is able to recycle nutrients very efficiently,
out competing other
tree species that depend on AM or saphro