BIOL 312 Population and Community Ecology Exam 2
Name___KEY______________
1) Chaparral communities are found in several regions of the world typified by hot, dry
conditions, such as southern California, South Africa, and western Australia. However, in many
areas, these systems, and the high native biodiversity in them, are being threatened by urban
development. A recent private holding in South Africa (20 hectares) has been sold to a
conservation advocacy group who want to preserve this community for future generations by
minimizing human impact. In other words, there will be no management other than to keep
people out. Based on your knowledge of chaparral ecosystems and succession, what do you
predict will happen to this area over the next 200 years? (6%)
Being such a small area, it is unlikely that natural fires will occur; this will lead to continued
succession (increase of woody species) and most likely, a drop in biodiversity (especially the
unique chaparral species dependent on fire for reproduction)
(I also gave partial credit for mentioning the need for fire that these systems have, and how fire
re-sets secondary succession in chaparral systems)
2) Discuss the different perspectives and debate on succession as described by Henry Gleason vs.
Frederic Clements in the 1910s. (4%)
Clements: ‘superorganism’ concept of communities, with intact climax communities as
endpoint of succession
Gleason: ‘individualistic’ concept of communities, with no concept of a ‘climax’
3) True or False: Succession involves dynamic processes of colonization and extinction of
species until a climax community is reached. (1%)
False (even climax communities still have colonization and extinction)
4) Give an example of each of the following types of mutualism: (3%)
Answers could vary
Transport- e.g., pollination (for plant), seed dispersal
Protection- e.g., clownfish/anemone, fig wasp larvae, ant/acacia
Nutritional: e.g., fig wasp larvae, pollination (for pollinator)
4b) For one of your examples above, list the costs and benefits for each species in the
mutualism. (4%)
Answers varied
4c) Explain how environmental factors, such as nutrient availability, might affect the
strength of one of your mutualisms listed above. (3%)
Answers varied, but I gave full credit if you said that when costs are greater than
benefits because of environmental factors, a mutualism switches to become a
parasitism
5) What is a trophic cascade? (2%)
An indirect effect where a predator reduces the abundance of prey and this cascades to
increase abundance in next lowest trophic level (and so on)
6) Why are trophic cascades more easily found in aquatic systems than in terrestrial systems?
(4%)
(any two of the following four reasons got you full credit)
-population dynamics at each trophic level are relatively fast
-trophic levels are discrete
-species interactions are strong
-(little is known about terrestrial systems, especially belowground…e.g., the Wardle
paper)
7) Recently, Gull Lake residents became concerned because of growth of large algal blooms in
the lake, which caused reduced water clarity and unpleasant swimming conditions. Based on
what you know of lake aquatic food webs, describe both a bottom-up and a top-down
explanation for these algal blooms. (4%)
Bottom-up: increased nutrient inputs (e.g. fertilizer runoff) caused increase in algae
Top-down: increased planktivorous fish due to stocking (or decreased piscivorous fish
due to overfishing) decreased zooplankton, which allowed algae to bloom
8) Tilman tested his resource ratio in two systems. Briefly explain each, indicate which one
supported his theory, and give reasons for why the theory worked in one system and not the
other. (5%)
He tested his ideas with algae in a chemostat and plants in a Minnesota old-field. The resource
ratio model worked for the protests probably because it was a well-mixed system (low
heterogeneity) and organisms had fast generation times that were likely to reach an equilibrium.
9) Briefly give five explanations for why many communities have higher species richness than
predicted by simple competition models (e.g. Lotka-Voltera). Full sentences are unnecessary.
(5%)
No age or genetic structure
No migration/dispersal
No time lags
Resources are limited supply
Alphas
Density dependence is linear
Spatial heterogeneity
Temporal heterogeneity
Disturbance
Predation
Aggregation
I decide that this question was a little vague to I also accepted some other answers that are not
technically correct but illustrate that you were aware of some of the issues.
10) Draw a graph illustrating MacAurthur and Wilson’s model of island biogeography. Label
the axes and draw a function for near, far, small, and large islands. Briefly explain how this
model might be applied to the design of nature reserves. (10%)
Small
Near
RATE
Large
Far
NUMBER OF SPECIES
S
Any logical connection between the model and
reserve design was given full credit
11) Explain what the target effect and rescue effect are and how they relate to MacAurthur and
Wilson’s model. (4%)
Target effect: immigration is higher on large than small islands because they are easier to find
(e.g. birds) or be ‘hit’ by wind dispersed species
Rescue effect: extinction rates are lower on large than small islands because they receive more
immigration potentially rescuing species that are nearing extinction
12) Assuming that two populations start at point A, what is the predicted competitive outcome?
(5%)
N2
K 1 /  12
80
60
K2
40
20
A
20
40
K1
60
80
N1
K 2 /  21
Two species will coexist. Intraspecific competition is higher than interspecific competition.
13) Based on the following figure, which species would you predict will win in competition?
(5%)
Birth rate of
species B
Mortality rate
of species B
Rate
Birth rate of
species A
Mortality rate
of species A
Resource Availability
Species A will out-compete species B because species A can maintain positive population growth
rates at lower resource levels than species B.
14) Give two reasons why diversity may be important to ecosystem functioning (1 sentence). In
class, we discussed two tests of this idea. Explain one and give the general result from the
experiment (3 sentences or less). (5%)
Complementarity, insurance effect. Tilman manipulated plant species in a Minnesota old-field
and looked at N cycling. He found higher productivity and less N loss with higher diversity.
Naeem manipulated diversity in three trophic levels in a growth chamber and found high
production in complex compared to simplified food web. (This turned out to be a difficult
question so we accepted answers that had at least one reason for the importance of diversity to
ecosystem function and correctly identified the diversity-ecosystem function experiment).
15) We discussed how species diversity relates to eight different environmental gradients. List
four of these environmental gradients and how one group or organisms (e.g. birds, mammals,
etc) relates to each gradient. (4%)
Latitude (S decreases with latitude: lizards, trees, butterflies, bivalves)
Succession (S increases with succession: birds, insects)
pH (S increases with pH: plants, inverts)
Disturbance (S is unimodal: algae, insects, phytoplankton)
Ocean/lake depth (S is negative to unimodal: megabenthos)
Temperature (S decreases with temp range: birds, mammals, gastropods)
Productivity (S increases with productivity: birds, mammals, amphibians, reptiles)
Elevation (S decreases with elevation: birds, mammals, plants
16) A friend is planning a trip across the U.S. and is looking for destinations that might have a
high diversity of mammals in their natural habitats. Where would you tell them to go and why?
(4%)
Southern, rocky mountains or mountains in California. Mountains have high heterogeneity
(many habitats compressed into small spatial area). Diversity often increases at lower latitudes.
17) Give a definition for a community. Include four ways that people have tried to define
communities. (5%)
Simplest definition: is a group of interacting organisms defined by physical, statistical,
taxonomical or by species interactions.
18) Copper sulfate is used to control weeds in lakes and ponds. A colleague wants to compare
zooplankton communities in lakes with or without copper sulfate but is not sure what to measure.
What are some of the options and what are the strengths and weakness of each? (5%)
One could measure species richness, evenness and composition. Some had trouble recognizing
that the question focuses on what to measure and how to compare communities. I accepted a
variety of answers that at least included richness and abundance.
19) What is the effect of the predator (Typhlodromus) on the prey (Eotetranychus)? (4%)
Introduction of predator leads to decreased amplitude and increased period. The predator did
NOT cause oscillations as the prey cycles in the absence of the predator
20) Organisms respond to predation in many ways. Provide four examples. (4%)
Masting, increased growth/flowering, chemical defense, physical defense, mimcry, intimidation,
group behavior, spatial separation, etc.
21) Louda examined the importance of herbivory from the coast to inland sites in California.
She used an insecticide to remove/reduce herbivores. What conclusions can you draw from this
study? (4%)
There were a wide variety of answers. I did not deduct points for this question.