Pool of Exercises for Communities and Ecosystems
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According to the nested plot technique, discuss the minimal sampling area in different plant
communities.
According to Wu’s system(1991), how many geographical genera components make up the
evergreen broad-leaved forest? And which is the dominant component?
All the keystone species work we have discussed in this chapter has concerned the influences
of animals on the structure of communities. Can other groups of organisms act as keystones?
What about parasites and pathogens?
As the concentration of atmospheric CO2 is increasing, what other pools of carbon will be
affected? In what ways?
Based on the fact that many nutrients (P, K, Ca, Mg, etc.) come from rock weathering and get
leached out of the land system through time, Why have not we seen any dead-end systems
that totally run out of these nutrients?
Biological interactions may also affect lake systems. How does the recent history of the Great
Lakes suggest that the kinds of species that inhabit a lake influence the nature of the lake
environment and the composition of the biological community?
Both abiotic and biotic factors influence birth and death rates in populations. Make a list of
abiotic and biotic factors that are potentially important regulators on the dominant canopy
species in subtropical broad-leaved forest.
Butterflies, which are ectothermic and diurnal, are found from the tropical rain forest to the
Arctic. They can elevate their body temperatures by basking in sunlight. How would the
percentage of time butterflies spend basking versus flying change with latitude? Would the
amount of time butterflies spend basking change with daily changes in temperature?
Can you use your own words summarizing the debate about the link between diversity and
stability?
Compare and contrast the characteristics (climate, plant types, animal life, soil types, etc.) of
the following biomes: Tundra, Temperate Deciduous Forest, Desert, and Tropical Rainforest.
Compare and contrast the function and structure of the grazing and detritus food chain.
Contrast the apporoches of C. Darwin and G. Mendel to the study of populations. What was
Darwin’s main discovery?
Describe how energy flows through ecosystems.
Describe the relationship between the number of plant species and plant biomass.
Design a planetary ecosystem based entirely on chemosynthesis. You might choose an
undiscovered planet of some distant star or one of planets in our solar system, either today or
at some distant time in the past or future.
Discuss Connell and Slatyer's three mechanisms of succession. Start your answer with a
definition and an example of what is succession, and describe how succession begins.
Discuss how much the current state of a aquatic community in the lakes depends on history.
Discuss in detail the nitrogen or carbon cycle. In your discussion be sure to explain how
humans have altered these systems.
Discuss the concept that ecosystems are essentially energy systems.
Discuss the different types of species interactions. Be sure to include in your essay
information on how each type of interaction between two species influences the fitness of
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each species.
Discuss the term dispersal. Include in your answer an explanation of why organisms want to
disperse, and how organisms accomplish this life history strategy.
Discuss what approaches a country might take to eliminate the introduction nonnative
animals and plants?
Do the data support or reject the hypothesis that there is no increase in the maximum biomass?
Does the answer to this question depend upon the year (if so, state how the years differ)?
Draw a typical soil profile, indicating the principal layer, or horizons. Describe the
characteristics of each layer.
Endler(1980) pointed out that through field observations are consistent with the hypothesis
that pradators may exert nature selection on guppy coloration, some other factors in the
environment could be affecting variation in male color pattern among guppy populations.
What other factors, especially physical and chemical factors, might affect male colors and
should each influence male color?
Evolution describes the process by which species come to possess adaptations. In an essay,
describe how evolution works through natural selection, spatial isolation, and gene mutation.
Explain in detail how energy moves through the grazing food chain and the detritus food
chain. Also, discuss how these food chains are related to each other and are necessary for the
cycling of nutrients in an ecosystem.
Field experiments demonstrate that variation in soil fertility influence terrestrial primary
production. However, we can not say that nutrients exert primary control. That role is still
attributed to temperature and moisture. Why do ecologists still attribute the main control of
terrestrial primary production to temperature and moisture?
How can the results of greenhouse experiments on competition help us understand the
importance of competition among natural population?
How do the following attributes control the population dynamics of a species: natality,
immigration, mortality and emigration.
How do you build the logistic equation for population growth from the exponential model?
What part of the logistic growth equation produces the sigmoidal growth curve?
How does competition differ from predation or parasitism?
How does the relationship between biomass and species richness change over time? How
does it stay the same? Do the standard error measurements change your interpretation of this
pattern? What is the advantage of having data from more than one or two years?
How does the relationship between species richness/productivity change over time?
How many plant functioning groups make up the Mangroves? How many geographical
components make up the mangroves?
How to get the ideal sediment samples for pollen research?
How to get the leave samples for population genetics research?
How to survey the tree population based on population dynamics?
How would you apply Connell’s intermediate disturbance theory to conservation and
agroecology?
How would you present the issue of carbon sequestration to the president of the United States
if you were chosen to do so?
If rates of decomposition are higher in an ecosystem with higher nutrient availability, how
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should nutrient enrichment affect rates of decomposition?
Imagine desert beetle that uses behavior to regulate its body temperature above 35℃. How
might this beetle’s use of microclimates created by shrubs, burrows, and bare ground change
with the season?
In most of the examples discussed in this chapter, we saw a close match between the
characteristics of organisms and their environment. However, natural selection does not
always produce an optimal, or even a good, fit of organisms to their environments. To verify
this you need only reflect on the fact that most of the species that have existed are now
extinct. What are some of the reasons for a mismatch between organisms and environments?
Develop your explanation using the environment, the characteristics of organisms, and the
nature of natural selection.
In most studies of plant community succession, researchers study succession by comparing
sites of different stages. This method is called “space for time substitution.” What are the
major assumptions of a space for time substitution?
In mutualism, species interactions are beneficial for all involved. Do mutualistic interactions
ever limit the distribution of a species?
Inouye and Taylor (1979) provided a reasonable representative of temperate ant-plant
protected mutualisms after research the relationship between ants and the aspen sunflower.
Compare this mutualism with that of the tropical mutualism between swollen thorn acacia
and ants.
Is a high degree of stability for an ecosystem always desirable?
Is there a carrying capacity for the whole living world at the biosphere level? Is there a
carrying capacity for the population of humans at the level of the planet earth?
List and briefly describe mutualistic relationships that seem to contribute to the ecological
integrity of biosphere.
List for plants and animals six reasons why the assumption that population growth at a given
point in time depends only on conditions at that time and not on past events might be
incorrect.
Many desert species are well waterproofed. Evolution cannot, however, eliminate all
evaporative water loss. Why not?
Many rivers around the world have been straightened and deepened to improve conditions for
navigation. Side effects of these changes include increases average water velocity and
decreased movement of water into shallow riverside environments such as eddies and
marginal wetlands. Discuss the probable influences of these changes on nutrient spiraling
length.
Many species of plants and animals that are associated with boreal forests also occur on
mountains far to the south of the boreal forests. Using what you have learned about
microclimates, predict how aspect and elevation would influence their distribution on these
southern mountains.
Mosser and collegues(1974) found that populations of the bacterium Sulfolobus living at
different temperatures had different optimal temperatures for sulfur oxidation. Use natural
selection to explain these patterns. Design an experiment to test your explanation. Assume
you can create artificial springs and regulate their temperature as you like.
Of three survivorship curves, type III has been the least documented by empirical data. Why
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is that?
Organic matter is continually being added to the surface of soils by way of wastes and death.
Why is the input of organic matter important in community and ecosystem function?
Pastor and Post (1988) state that “the carbon and nitrogen cycles are strongly and reciprocally
linked.” Review the nitrogen cycle and discuss these linkages.
Plant populations respond to crowding by reducing the biomass of individuals. The
relationship between plant density and individual biomass has been called the -3/2 power law
of plant thinning. Discuss this case with the Chinese fir trees in its forest.
Some plants and grasshoppers in hot environments have reflective body surfaces, which
make their radiative heat gain, Hr, less than it would be otherwise. If you wrer to design a
tiger beetle that could best cope with thermal conditions on black beaches, what color would
it be? The beetles on the white beaches are white. What do the matches between the color of
these beetles and their beaches tell us about the relative roles of thermoregulation and
predation pressure in determining beetle color? What does this example imply about the
ability of natural selection to “optimize” the characteristics of organisms?
Species vary in abundance both spatially and temporally. Further, we can generalize that a
species will occur only where and when: (a). It is capable of reaching a location; (b).
Appropriate conditions and resources exist for survival; and (c). Interspecific interactions do
not preclude it.
Spruce trees occur all the boreal forest and on mountains farther south. How do you think
they would be distributed in the mountains that rise from the southern deserts? In particular,
how do altitude and aspect affect their distributions in the southern part of their range? Would
spruce populations be broken up into small populations in the southern or the northern part of
the range? Why?
The applications and tools section reviews how the studies of Bruno Baur and Anette
Baur(1993) have documented the local extinction of the land snail Arianta arbustorum. Their
research also shows that these extinctions may be due to reduced egg hatching at higher
temperatures. Do these results show conclusively that the direct effect of higher temperatures
on hatching success is responsible for the local extinctions of A. arbustorum? Propose and
justify alternative hypotheses. Be sure you take into account all of the observations of the
Baurs.
The dams that have been built on many rivers often stabilize river flow by increasing flows
blow the dam during droughts and decreasing the amount of flooding during periods of high
rainfall. Explain how these flows can be considered as a “disturbance.” Using the
intermediate disturbance hypothesis, predict how stabilized flows would affect the diversity
of fishes below reservoirs.
The discussion of seed size and number focused mainly on the advantages associated with
large seeds. However, research by Westoby etc. has revealed that the plants from widely
seperated geographic regions produce a wide variety of seed sizes. If this variation is to be
maintained, what are some of the advantages associated with producing small seed?
The section on avoiding temperature extremes focused mainly on animals. What are some of
the ways in which plants avoid temperature extremes? Bring cold and hot environments into
your discussion. Some of the natural history included in chapter 2 might be useful as you
formulate an answer.
66. Understanding biogeochemical cycling in an ecosystem requires complete knowledge of the
inputs and outputs to that ecosystem. With the aid of diagrams and examples, discuss the
cycling of a nutrient in a typical ecosystem focusing on the concept of inputs and outputs to a
system.
67. We focused much of our discussion of biomes on their latitudenal distribution. The
reasonably predictable relationship between latitude and temperature and precipitation
provide link between latitude and biomes. What other geographic variable might affect the
distribution of temperature and precipitation and, therefore, of biomes?
68. What are some of the major components of ecosystems? How are these components related
to each other?
69. What conclusions can you draw, or hypotheses can you make about the effect of the loss of
biodiversity in natural systems? What are the problems that need to be considered when
extrapolating the results of this experiment to natural systems?
70. What is a keystone species? Paine(1966, 1969) experimented with two starfishes that act as
keystone species in their intertidal communities along the coast of North America and in New
Zealand. Discuss the keystone species in subtropical plant communities in China.
71. What is an ecological niche? How do fundamental and a realized niches differ?
72. What is an ecosystem? How does it differ from a community? What are some of its important
components?
73. What is plant succession? What are the differences between a primary and a secondary
succession? How does facilitated succession work?
74. What is species evenness? How does each of its components of species diversity contribute to
the value of the Shannon-Wiener index(H’)?
75. What is species richness? How can we survey it? Campare the richness of Mt. Wuyishan and
Mt. Changbaishan.
76. What is the relationship between species richness (the number of species) and productivity
within this savannah grassland?
77. What kinds of interactions within an plant or animal population lead to clumped
distributions?
78. What seven conditions are required to define something as living?
79. What values of R0 indicate that a population is growing, stable, or declining? What values of
r indicate a growing, stable, or declining population?
80. What will happen if we humans overshoot the carrying capacity if it exists as a hard limit?
81. What will happen to the global nitrogen cycle if the same amount of synthetic nitrogen
fertilizers will be used worldwide for the next thousand years?
82. When we reviewed how some organisms use torpor, hibernation, and estivation to avoid
extreme temperatures, we discussed the idea of energy savings. However, organisms do not
always behave in a way that saves energy. For instance, when food is abundant
hummingbirds do not go into torpor at night. This suggests that there may be some
disadvantages associated with torpor. What are some of those potential disadvantages?
83. Why might a diverse plot contain more biomass than even the highest monoculture plot?
Why might two species be better than one when it comes to biomass production?
84. Why should we be careful of introducing exotic animals and plants into habitats where they
never existed before?
85. With the aid of a diagram explain the ecological niche concept. Also, discuss in your essay
the difference between the fundamental and realized niche, and the relationship between
niche and tolerance range.
86. What are inland wetlands, and what important role do they play?
87. What are coral reefs? How are they formed, and what major services do they provide? Whay
harmful impacts do human activities have on coral reefs?
88. Distinguish between rocky shores, clay shores and sandy shores, and describe the major types
of community found in each?
89. Why does the mangroves evolved the supported roots?
90. What is a forest? What are the major four types of forest, and how do they differ in climate
and biological makeup? What types of human activities have harmful impacts on forests?
91. What is a grassland? What are the major type of grassland, and how do they differ in climate
and biological makeup? Why are grasslands vulnerable to disruption, and what types of
human activities have harmful impacts on forests?
92. What is a deaert? What are the major types of desert, and how do they differ in climate and
biological makeup? How do desert plants and animals survive?