Download Chapters 25-27 sample exam

Integrating Concepts in Biology II
Answer Key for Sample Exam covering Chs 25-27 on Emergent Properties of populations/ecological
systems
Instructions for Instructors: This sample exam KEY covering Chapters 25-27 of ICB can be used as a
guide to grading. You might be looking for something more specific and because some of the
questions are open-ended, other answers not provided here might also be correct. See the ICB
approach to assessment guide in the Instructor Resource area for more information
1. (CH25) What is the evidence that the multiple fungal samples from a forest in Michigan came
from the same individual and not from several related individuals? Use data from Data Gallery #1
to support your answer.
Anderson and colleagues only found two alleles at each self-incompatibility locus from samples over a
wide area (TABLE 25.1 and FIGURE 25.1), leading to the possibility that these samples were from the
same individual. The RFLP and RAPD data helped support the conclusion that these samples were all
from the same individual. Only two alleles were found in each restriction enzyme locus in all samples
found within the individual 1 boundary, further supporting the conclusion that only one individual was
present.
2. (CH25) Choose one of the estimates of growth rate of fungus from different methods to estimate
the age of a large fungus growing in a forest. The width of the area the fungus was known to be
growing in was 635 meters across, and you can assume that the fungus is in a circle that grew at
the same rate in all directions. Use data from Data Gallery #1 to support your answer.
Calculate the annual growth rate of laboratory cultures using the daily growth at 15 o C for 90 days,
which is 0.189 m/year (TABLE 25.21). This is quite comparable to the annual growth on wooden stakes in
the forest soil (0.197 m/year). If this individual fungus grows in all directions at the same rate from a
central point, it would be circular, and the maximum distance across would be the diameter of the circle.
The radius is half of that, which is the maximum distance it grew during its life. If it grew steadily at
0.193 m/year (the average of the two estimates made by the scientists), then this fungus is 1,645 years
old [(635 m/2)/(0.193 m/year)]. If they used only one or the other of the estimates, the estimate would
be slightly different: [(635 m/2)/(0.189 m/year) = 1679 years, or (635 m/2)/(0.197 m/year) = 1611 years].
3. (CH25) What conclusions can you draw from microsatellite data taken on aspen trees in terms of
number of individuals in a forest? What evidence did you use to draw your conclusion? Use data
from Data Gallery #1 to support your answer.
Mock and her colleagues concluded that there were up to 41 individual aspen in this forest, which is far
fewer than the 209 stems sampled (TABLE 25.3). Most of the forest was made up of just one individual
(FIGURE 25.5). Although they did not sample the entire forest and could not determine the extent of the
other individuals, none of them could be as large as this one, based on the total size of the aspen forest.
The researchers concluded that all 141 trunks with the same genotype plus the five trunks that differed
from the dominant genotype at only one allele belonged to the same individual, because the probability
of seeing identical genotypes in two unrelated individuals is very small. The samples that differed by
four to seven alleles were from 40 different individuals found in 63 trunks. Some of these individuals
were single stems, but some were made up of several trunks (TABLE 25.3 and FIGURE 25.5).
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4. (CH25) What other Big Ideas in addition to Emergent Properties can you relate to how the
individual is an emergent property of a set of smaller parts?
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


Information: components of systems, whether cells in a body or species in an ecological system,
exchange information with each other and these interactions may produce the emergent property.
Evolution: like other properties, EPs are also subject to adaptation and other mechanisms of
evolution.
The cell: In multicellular individuals the cells are components of organisms and emergent properties
arise from interactions and functions of cells and their components.
Homeostasis: maintenance of homeostasis may actually be an emergent property, caused by
interactions and mechanisms in components of organisms.
5. (CH25) Describe the similarities and differences in physiological responses to fear and anger in
humans. Relate physiological responses to expressive behaviors observed when animals or
humans are frightened or angry, and consider the adaptive value of these responses for the
emotions of fear and anger. Use data from Data Gallery #1 to support your answer. Answer in
no more than three sentences.
There were strong similarities in physiological responses to fear and anger (FIGURE 25.9). There were
increases above the resting values in each of the variables measured. Although there were some
similarities in physiological response between fear and anger, increases in diastolic blood pressure were
greater in the anger response than in the fear response. The number of muscle tension peaks and
increases in respiration rate and skin conductance were greater in the fear response than in the anger
response. Measurable physiological responses resulted from stimuli that evoked fear and anger.
6. (CH25) Are there expressions that are unique to a basic emotion? If not, might there be a way to
uniquely infer an emotion from expressive behaviors? Are there emotions that are unique to a
particular species?
There are sets of expressions that could be unique, although there is a lot of overlap in how single
expressions were categorized by Darwin (TABLE 25.4). Fear is indicated by the set of trembling,
sweating, vocalizations, facial expressions, and rising of the hair. Many animals use the same or similar
combinations when confronted by a predator or a dominant individual. Although vocalizations and facial
expressions also indicate other emotions, it is the set of vocalizations and facial expressions that are
important in deciding on or interpreting a particular emotion. So animals use the set of expressions as a
way to infer emotion from other individuals. To infer an emotion from a single expressive behavior
requires other cues from the environment to put the expression into context (for instance, presence of a
predator in the area). Animals of many different species use similar expressions to convey information
on the emotion they might be experiencing (TABLE 25.4).
7. (CH25) What is the evidence that the splanchnic nerve stimulates the adrenal gland? Use data
from Data Gallery #1 to support your answer. Answer in no more than two sentences.
Adrenalin is released from the adrenal gland and causes changes in physiology and expressive behavior
(TABLE 25.5 and FIGURE 25.11). It is associated with the fight-or-flight response in animals. You
concluded that anesthetized dogs not experiencing any emotions can be stimulated to release a
substance from the adrenal gland into the blood that causes increases in heart rate and blood pressure,
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much like adrenalin does. This substance, of course, is adrenalin. The stimulation of the splanchnic nerve
caused release of adrenalin.
8. (CH25) Describe differences in the social structure and life cycles of P. fuscatus and P. canadensis.
Use data from Data Gallery #1 to support your answer. Answer in no more than three (3)
sentences.
P. fuscatus has fewer foundresses than P. canadensis (FIGURE 25.14). Colony sizes are typically bigger
and more strongly related to number of foundresses in P. fuscatus than in P. canadensis. Average cells
per foundress are also greater in P. fuscatus than in P. canadensis. Colonies are more or less year round
in P. canadensis, a tropical species, whereas they are more seasonal in P. fuscatus (FIGURE 25.16
partially supports this).
DATA GALLERY #1
Table 25.3
Table 25.2
Table 25.1
Figure 25.2
Figure 25.5
Figure 25.9
Figure 25.10
Figure 25.11
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Table 25.4
Table 25.5
Figure 25.12
Figure 25.13
Figure 25.14
Figure 25.17
Table 25.6
Figure 25.15
Figure 26.3
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Table 26.1
Table 26.2
Figure 26.2
Figure 26.6
Figure 26.4
Figure 26.5
Table 26.3
Table 26.4
Figure 26.8
Figure 26.9
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Figure 26.10
Figure 26.7
Table 26.5
Table 26.6
9. (CH25) Provide evidence that cooperation occurs among members of a plant population. Use data
from Data Gallery #1 to support your answer. Answer in no more than two sentences.
Damage to unclipped plants or branches on the same plant is reduced when downstream from a
damaged branch on same or different sagebrush plant (FIGURES 25.12 and 25.13). This suggests that
some volatile chemical is released when a plant is damaged by an herbivore and this chemical is
detected by other branches on same plant or neighboring plants within a certain distance, less than 60
cm away (FIGURE 25.12B).
10. (CH26) Since the time research on the Brazilian water hyacinth was performed, 25 years ago,
northeastern Brazil has been further fragmented by deforestation and road-building. Given what
you know about the dynamics of this species and metapopulation dynamics in general, predict
what will happen to the water hyacinth metapopulation as the lowland forest becomes more
encroached upon by humans. Use data from Data Gallery #1 to support your answer. Answer in
no more than three sentences.
It can be argued either way, if properly supported by data. For instance, a student could argue that
fragmentation will lead to isolation of habitats, reducing density of patches and consequently reducing
density of subpopulations (FIGURE 26.9C and D). Alternatively, more development leads to more roads
and this might actually increase number of patches in ditches along roads. While these may be small
patches, there is not a clear relationship between size of subpopulation and persistence (FIGURE 26.9A
and B) but if density of patches increases, then density of subpopulations should as well (FIGURE 26.9C
and D). Population persistence is generally low, but persistence is high (TABLE 26.5), suggesting perhaps
that once a population is established it will remain for some time.
11. (CH26) Regarding the age structure, as illustrated for pumpkinseed sunfish, is there a relationship
between mass and age of fish, and if so what is it? How do mass, age structure or the relationship
between the two variables vary, if at all, among the different populations (lakes)? What does that
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suggest about the lakes as habitats for sunfish? Use data from Data Gallery #1 to support your
answer. Answer in no more than two sentences.
Sunfish from Little Round Lake and Warrens Lake matured earlier than those from other populations
(FIGURE 26.2), females exhibited a high GBM, and adults were smaller than fish from other populations
(TABLE 26.1). Sunfish from Vance Lake matured later, had a lower GBM, and adults were larger. Sunfish
from Beloporine and Black Lake had traits intermediate to those of the other populations. FIGURE 26.2
shows a strong relationship between length and age of fish. Sunfish in some lakes grow faster than
others, as indicated by the slopes of length versus age. There are likely to be different conditions in the
lakes. The presence of predatory fish could cause a different age structure by selecting for individuals
that mature earlier. Little Round and Warren Lakes have lower slopes, indicating that they are smaller
than sunfish from other lakes at each age, and they also mature earlier. Populations of large fish mature
later. This suggests a relationship between size and age at maturity driven by environmental conditions.
12. (CH25) Use all three of the following data figures to argue that a honey bee hive is an emergent
property. Answer in no more than three (3) sentences.
Figure 25.6 Infrared thermogram of honey bees.
Figure 25.8 Percentage of bees with thorax temperatures 0.2oC above head and 1.0oC above
abdomen temperature at five hive temperatures.
Figure 25.7 Thorax temperatures of worker honey bees in different hive locations.
Honey bee colonies represent an emergent property because individual honey bees work together to
maintain the hive temperature within a certain range. Specifically, when a honey bee hive is stressed by
cold temperatures, workers respond by generating heat. At low experimental temperatures, all hive air
and cell rim temperatures were above the experimental temperature, although cells that contained
developing larvae and pupae were kept the warmest (FIGURE 25.7). Not all bees are generating heat at
the same time (FIGURE 25.6). The generation of body heat is primarily accomplished using large thoracic
flight muscles. Worker bees older than 2 days are much more likely to be involved in metabolic heat
production than bees less than 2 days old (FIGURE 25.8). Workers near the brood cells are generating
more heat than workers in other areas, and these are primarily older workers. The hive is a property
that emerges from a collection of honey bees, each a part of the whole, and the properties of the hive
are greater than the sum of the parts.
13. (CH25) Using the data below answer the following questions:
a. Briefly describe the treatments and controls of one of the experiments below, and the major
conclusion of the experiment.
FIGURE 25.12B shows the results of an experiment using pairs of individual plants. One individual from
each plant upwind of the other had a branch either clipped or not. Then a branch on the other individual
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of the pair, the downwind individual, was monitored for herbivore damage. It shows that the downwind
individual had less damage if it was paired with a clipped individual within 60 cm.
FIGURE 25.13A shows a similar experiment, where an individual was either clipped or not and upwind or
downwind of another individual in a pair. Individuals downwind from a clipped individual suffered less
damage than either individuals paired with an unclipped plant or a clipped, upwind individual,
suggesting an airborne cue.
FIGURE 25.13B shows an experiment a different branch on same individual that was clipped or a branch
on another individual nearby a clipped individual was assessed. Some branches that were clipped were
bagged. Branches of clipped individual and individuals near the clipped individual received less damage
ONLY when the branch was not bagged. Bagging the clipped branch had the same effect on other
branches as the control, further supporting the conclusion that a volatile chemical was released by the
clipped plant/branch.
b. Describe three (3) Big Ideas of biology to which these experiments relate (1 short phrase for
each Big Idea).
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
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
Information: individual plants or branches on the same plant communicate by releasing a volatile
compound when attached by an herbivore; other branches and plants receive that information and
react accordingly.
Evolution: the chemical communication system evolved in individuals, we think because the vascular
system was not efficient to convey the information to other parts of the same plant.
The cell: the chemical is produced in cells and then released into the extracellular fluid, and then it is
secreted from the plant.
Homeostasis: maintenance of homeostasis may be enhanced through the use of this communication
system.
Figure 25.12
Figure 25.13
14. (CH25) Compare the two paper wasp species in terms of their colony sizes and cells per
foundress using the data in Figure 25.17. In particular, address the costs and benefits as the
number of foundresses at a colony increase, both from an individual foundress perspective and at
the colony level. Answer in no more than three (3) sentences.
Figure 25.17 Relationship between colony size and number of foundresses for
two species of paper wasp (P. fuscatus is temperate, P. canadensis is tropical).
Polistes canadensis tends to have fewer offspring in each colony but has more
foundresses than P. fuscatus. Only rarely did colonies of the former have just
one foundress, although that was common for P. fuscatus. Scientists concluded
that the differences were probably climate or habitat related. Ecological
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interactions, such as competition or predation, could lead to situations where it is advantageous to have
more or fewer foundresses. More foundresses might be advantageous in situations where there is a high
probability that foundresses are related, a large proportion do not have well-developed ovaries, or there
is high competition for resources. But more foundresses in P. fuscatus colonies led to a disadvantage in
that the number of offspring per foundress declined dramatically. Fewer foundresses per P. canadensis
colony produced fewer offspring per colony than when P. fuscatus had only one or two foundresses, and
the disadvantage to having more foundresses was not as great as for P. fuscatus colonies.
15. (CH26) What differences in age distributions do you observe over time within a lake? What
differences do you observe among lakes? Use data from Data Gallery #1 to support your answer.
Answer in no more than two sentences.
Over time most lakes had fairly stable age distributions although there were some annual fluctuations
evident for some lakes. There was greater variation evident between lakes. Some lakes had no or very
few individuals of age 6, while others had larger proportions of age 6 individuals. The actual sizes of the
populations varied quite a bit, too. Some had a rapid dropoff of individuals between ages 3 and 4.
FIGURE 26.3 supports these statements.
16. (CH26) Given the density that was estimated for the black-lipped lizard, the extent of the cloud
forest, and human encroachment into the forest, do you consider this species to be in danger of
extinction? Why or why not? What evidence do you have from the data that indicates the stability
of the population? Use data from Data Gallery #1 to support your answer. Answer in no more
than three sentences.
It could be in some danger given that it is only found in one cloud forest, were that forest to be logged or
extensively damaged by humans (FIGURE 26.5). In such situations with endemic species with small
geographic ranges there is always the danger that habitat loss will result in extinction. However, given
the density of the population seemed stable over the length of the study in terms of gender ratio and
size of population (TABLE 26.4 and FIGURE 26.6).
17. (CH26) Compare and contrast demographics of populations and metapopulations. What
additional data are needed to accurately describe a metapopulation in comparison to a
population? Use data from Data Gallery #1 to support your answer. Answer in no more than two
sentences.
Single populations, such as seen with black-lipped lizard, don’t have colonization or extinction of
subpopulations or migration between subpopulations because they have no subpopulations (FIGURES
26.5 and 26.6). Their demographics are based only on what is occurring in that population, whereas
metapopulation demographics will also depend on movement between subpopulations. Those
additional factors of subpopulation persistence, extinction rates, colonization rates, patch density, and
migration are needed to fully understand the dynamics of metapopulations (FIGURES 26.9 and 26.10 and
TABLES 26.5 and 26.6). Subpopulations may vary independently of one another (FIGURE 26.8 and TABLE
26.6, e.g.).
18. (CH26) What are the relationships between colonization and extinction rates and the size of a
subpopulation? What are the implications of either of these relationships to metapopulation
structure and persistence of subpopulations? Use data from Data Gallery #1 to support your
answer. Answer in no more than three sentences.
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There was a negative linear relationship between extinction rate and density of subpopulations. The
colonization rate results were mixed. There was a negative relationship between colonization rate and
the logarithm of population density for north-facing slope subpopulations (FIGURE 26.10). There was a
slightly positive slope for the relationship between colonization rate and population density for southfacing slopes, but researchers determined that the slope was not significantly greater than 0, suggesting
no relationship. Population size is an important factor determining extinction rates and most species
had higher extinction than colonization rates. Local extinction occurs often and persistence of
subpopulations over long periods of time is driven by repeated colonization. In addition, extinction rates
differ in habitat patches of differing quality. Higher extinction rates in south-facing slope habitats leads
to smaller populations. Smaller populations are more vulnerable to catastrophic or random disturbances
that could cause local extinction. Although population size was not related to subpopulation extinction
for the Brazilian water hyacinth (FIGURE 26.9A and B), the trend for five species in FIGURE 26.10 is that
extinction rate is inversely related to population size or density. Isolation of small subpopulations (such
that colonization is largely prevented) would increase the likelihood of local extinction.
19. (CH26) Describe how the spatial structure of a single population differs from that of a
metapopulation and how differences in spatial structure affect the growth of the population. Use
data from Data Gallery #1 to support your answer. Answer in no more than three sentences.
For a single populations, the spatial structure is all in one area, or one habitat patch, whereas a
metapopulation may exist in many such patches scattered across a heterogeneous landscape (FIGURES
26.5 and 26.7). Population growth of a single population is dependent on the species and the resources
in that one patch, whereas growth of a metapopulation is also dependent upon movement between
subpopulations. Those additional factors of subpopulation persistence, extinction rates, colonization
rates, patch density, and migration are needed to fully understand the dynamics of metapopulations
(FIGURES 26.9 and 26.10 and TABLES 26.5 and 26.6). Subpopulations may vary independently of one
another (FIGURE 26.8 and TABLE 26.6, e.g.).
20. (CH26) Explain two of the rules of thumb that birds use when flocking. Use data from Data Gallery
#2 to support your answer. Answer in no more than three sentences.
Birds follow a leader and keep track of what that leader is doing, leading to a slight time delay in change
of direction or speed by a leader and the followers. There is a hierarchical network within the flock, but
the rule of thumb if you’re not a leader is to follow a leader (FIGURE 26.12). The second rule is that birds
keep track of their nearest neighbors, up to a limit of about 6 or 7 (FIGURE 26.16A). They also don’t keep
their nearest neighbor right in front of them (FIGURE 26.15).
21. (CH26) Show that starlings use the number of nearest neighbors, and not the distance apart
between nearest neighbors, to maintain cohesion while flocking. Explain the value of remaining in
a flock. Use data from Data Gallery #2 to support your answer. Answer in no more than three
sentences.
Starlings keep track of their nearest neighbors, up to a limit of about 6 or 7 (FIGURE 26.16A). They also
don’t keep their nearest neighbor right in front of them (FIGURE 26.15). There is no relationship
between the interaction range and the density of the flock, suggesting that the distance apart of
individuals does not matter, but the number of birds does. If interactions depend on distance, then the
distance (dc) would be the same for both flocks, although the number of individuals within this distance
would be larger in the denser flock than in the sparser flock. But there is a relationship between critical
distance and sparseness of flock (FIGURE 26.16D). If the interaction depends on topology, nc would be
the same for all flocks, thus making the critical number of interactions constant, even though the
distance (dc) to the ncth neighbor would be small in the denser flock and large in the sparser flock. The
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value of remaining in a flock is probably protection against predation, as shown in simulations that
supported the topology hypothesis (FIGURE 27.17C and E).
22. (CH27) Summarize the effects of the reintroduction of wolves to Yellowstone National Park. Use
data from Data Gallery #2 to support your answer. Answer in no more than three sentences.
Reintroducing wolves into YNP led to multiple effects on the ecological system. The elk population
declined (FIGURE 27.2), elk changed their foraging behavior (FIGURES 27.6 and 27.7), trees such as aspen
and cottonwood regrew in areas where elk presence declined or predation risk was higher (FIGURE
27.8), and shrub height and diversity increased (FIGURE 27.9). In addition, other animal species were
affected, such as beaver, which recolonized streams in the area (FIGURE 27.10).
23. (CH27) Scientists concluded that the loss of wolves from Yellowstone National Park probably
caused the lack of cottonwood maturation in some areas. Support this claim using data from Data
Gallery #2 to support your answer. Answer in no more than three sentences.
Analysis of the age distribution of a stand of cottonwood shows that missing diameter age classes, which
should be there based upon knowledge of past regeneration, began to become missing right about the
time that the last wolves were extirpated from the park (FIGURE 27.3). This allowed elk to roam freely
with little predation risk. In addition, in other stands where elk were excluded from stands, there were
no missing age classes (FIGURE 27.5).
24. (CH27) Make the connection between wolves and plant diversity using data from Data Gallery #2.
Be concise but thorough.
Reintroducing wolves into YNP led to multiple effects on the ecological system. The elk population
declined (FIGURE 27.2) and they changed their foraging behavior (FIGURES 27.6 and 27.7). Trees such as
aspen and cottonwood regrew in areas where elk presence declined or predation risk was higher
(FIGURE 27.8), and shrub height and diversity increased under aspen trees that were taller and had
regrown to a greater extent (FIGURE 27.9).
25. (CH27) Provide evidence from Data Gallery #2 that the outcome of competition is often
dependent upon environmental conditions. Be concise; answer in no more than three sentences.
Even though some plants were shown to be superior competitors in a nutrient-rich soil (TABLE 27.1 and
FIGURE 27.12A), poorer competitors were still found and actually did quite well in nutrient-poor
conditions (FIGURES 27.11 and 27.12B). Competitive ability may actually vary depending upon the
environmental conditions, in this case soil conditions. In another case, myna birds were shown to be
better competitors for nest box sites but the strength of competition varied with tree density. Clearing
of forests leads to habitats with lower densities of trees and thus fewer nesting cavities. The common
myna preferred low density forests and had densities about ten times higher in those forests. High
densities of myna led to high percent occupancy of nest boxes and greater success of eggs. Something in
the low density forests allowed myna birds to be more successful (FIGURES 27.13 and 27.14).
26. (CH27) Explain how the outcome of a competitive battle between two species may be different
under different conditions. Explain what those conditions are and how the outcome changes. Use
data from Data Gallery #2 to support your answer. Answer in no more than three sentences.
Two species of plants competing for space along a lakeshore: some plants in this habitat were shown to
be superior competitors in a nutrient-rich soil (TABLE 27.1 and FIGURE 27.12A). Loosestrife had a high
competitive ability and pipewort a low competitive ability, but pipewort was much more likely to occur
in soils with low organic matter content than loosestrife (FIGURE 27.11). Conversely, in soils with high
organic matter, loosestrife was nonexistent but loosestrife had a high probability of occurrence.
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In another case, as myna bird nest box occupancy increased, crimson rosella abundance declined and
myna occupancy was related to density of forests. Clearing of forests leads to habitats with lower
densities of trees and thus fewer nesting cavities. The common myna preferred low density forests and
had densities about ten times higher in those forests. Something in the low density forests allowed
myna birds to be more successful (FIGURES 27.13 and 27.14).
27. (CH27) Give an example of how a species that is considered a good competitor could actually lose
in a competitive battle with another species. Use data from Data Gallery #2 to support your
answer. Answer in no more than three sentences.
Similar to previous question, just a different way of wording the question.
Two species of plants competing for space along a lakeshore: some plants in this habitat were shown to
be superior competitors in a nutrient-rich soil (TABLE 27.1 and FIGURE 27.12A). Loosestrife had a high
competitive ability and pipewort a low competitive ability, but pipewort was much more likely to occur
in soils with low organic matter content than loosestrife (FIGURE 27.11). Conversely, in soils with high
organic matter, loosestrife was nonexistent but loosestrife had a high probability of occurrence.
In another case, as myna bird nest box occupancy increased, crimson rosella abundance declined and
myna occupancy was related to density of forests. Clearing of forests leads to habitats with lower
densities of trees and thus fewer nesting cavities. The common myna preferred low density forests and
had densities about ten times higher in those forests. Something in the low density forests allowed
myna birds to be more successful (FIGURES 27.13 and 27.14).
DATA GALLERY #2
Figure 26.11
Figure 26.12
Figure 26.14
Figure 26.15
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Figure 26.16
Figure 26.17
Figure 27.5
Figure 27.3
Figure 27.6
Figure 27.2
Figure 27.7
Figure 27.8
Figure 27.9
Figure 27.10
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Table 27.1
Table 27.2
Figure 27.11
Figure 27.12
Figure 27.13
Figure 27.14
Figure 27.15
Figure 27.16
Table 27.3
Figure 27.17
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Figure 27.18
Figure 27.20
Figure 27.19
Figure 27.22
Figure 27.23
Figure 27.24
28. (CH27) Compare and contrast two food webs in terms of energy pathways, numbers of species
and numbers of trophic levels. What might explain the differences you observe? Use data from
Data Gallery #2 to support your answer. Answer in no more than three sentences.
There are three trophic levels in the Washington State rocky intertidal food web and five in the Gulf of
California rocky intertidal food web. The Washington State food web contained 11 species, 18.2% of
which were carnivores, and the Gulf of California food web contained 45 species, 15.6% of which were
carnivores (FIGURES 27.15 and 27.16). Fewer species leads to fewer pathways for energy to flow and
fewer trophic levels. Generalist predators like Pisaster and Heliaster can even prey upon other
predators, leading to more complex pathways.
29. (CH27) Give an example of the effects of the loss of a top predator from an ecological system, and
compare that to an example where a top predator has been added to an ecological system. Use
data from Data Gallery #2 to support your answer. Answer in no more than three sentences.
Compare the exclusion of Pisaster from rocky intertidal zone with the reintroduction of the gray wolf to
YNP. Excluding Pisaster led to loss of diversity and dominance by a competitively superior bivalve (TABLE
27.3). Reintroducing a top predator, the gray wolf, caused diversity to rise in plant species.
Reintroducing wolves into YNP led to multiple effects on the ecological system. The elk population
declined (FIGURE 27.2), elk changed their foraging behavior (FIGURES 27.6 and 27.7), trees such as aspen
and cottonwood regrew in areas where elk presence declined or predation risk was higher (FIGURE
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27.8), and shrub height and diversity increased (FIGURE 27.9). In addition, other animal species were
affected, such as beaver, which recolonized streams in the area (FIGURE 27.10).
30. (CH27) Discuss the phrase “interaction strength.” What is the difference between an interaction
with strength of zero, a weak interaction, and a strong interaction? Use data from Data Gallery #2
to support your answer. Answer in no more than three sentences.
Interaction strengths are not exactly the same as energy flow, but the two measures are related.
Scientists analyzed a large food web by quantifying the per capita interaction strengths between all
predator-prey links and calculated a standardized measure of interaction strength of predators on their
prey. The goal was to use estimates of consumption to biomass ratios to obtain measures of energy
transfer that the scientists then standardized to per capita effects of predators on prey populations. An
IS = 0 means the two species did not interact at all, a weak IS means the predator occasionally consumes
the prey, and a strong IS means the predator consumes a high proportion of that prey’s population
biomass. Strong ISs are shown in FIGURES 27.15 and 27.18 and TABLE 27.2, although for some of those
data, it is not IS that is shown, but calories or numbers consumed.
31. (CH27) What are the implications to energy flow when strongly interacting two-link food chains
occur less frequently than expected by chance? Use data from Data Gallery #2 to support your
answer. Answer in no more than three sentences.
The 25% of interaction strengths classified as strong (Class 4; FIGURES 27.17 and 27.18) were less likely
to be found together in the same two-link chain than by chance. You might conclude that this might help
maintain energy flow homeostasis in ecological systems. Much of the energy of an ecological system
flows through pathways of predators and prey that interact strongly, but because strong interactions are
dispersed throughout the food web, eliminating one predator or another high on the food chain may not
result in a drastic effect on energy flow in the system. Because most two-link food chains contain only
one or no strong interactions, the likelihood of trophic cascades due to the loss of a top predator is
reduced. But fishing selectively targets a set of species in upper trophic levels that tend to be part of
strongly interacting two-link food chains. The scientists found that ten fish species currently under heavy
fishing pressure accounted for 48% of the strong interactions in two-link food chains. Of these food
chains, 31% had a buffering effect from strong omnivory, and 69% had potential for trophic cascades.
For this question, the data are in the text and may need to be added to the question.
32. (CH27) What are the implications to energy flow if a top predator that interacts strongly with its
prey is eliminated from an ecological system? What if both links in a two-link food chain had high
interaction strength? Relate to the elimination of Pisaster in Paine’s study. Use data from Data
Gallery #2 to support your answer. Answer in no more than two sentences.
If a top predator is eliminated, such as the one shown in FIGURE 27.18, middle top predator, a trophic
cascade may result. If both links are strong this could even more strongly lead to a trophic cascade,
although if there are alternate pathways provided by omnivory, energy may flow through these
pathways reducing the potential for a trophic cascade. This was related the experiment excluding
Pisaster because most of the energy in the system flowed up to Pisaster (FIGURE 27.15) and that led to
loss of diversity and dominance by a competitively superior bivalve (TABLE 27.3).
33. (CH27) What happens to the 81% of chemical energy produced by cordgrass that is not turned
into biomass? Consider other ways that plants use energy. Use data from Data Gallery #2 to
support your answer. Answer in no more than two sentences.
Biomass is production in this case; the 81% of the energy not used in production is used up in respiration
(FIGURE 27.24), for daily maintenance, biochemical reactions, etc.
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34. (CH26) Explain how the two age distributions shown can be used to
predict future population growth, and list two policies that a country may
use to affect growth of its population. Answer in no more than two
sentences.
Pyramid shaped age distributions, like the one for India on the bottom will
likely lead to high population growth, as there are high proportions of young
individuals about to enter their reproductive years. Age distributions like
China’s at the top are more likely to exhibit slower population growth in the
future as there are smaller proportions of individuals in the younger age
classes. Government policies that might affect growth of populations include
forced sterilization, punishments or disincentives for having too many children, incentives or rewards for
spacing out births or having fewer children, mandatory education of boys and girls, etc.
35. (CH27) Discuss the differences between assimilation efficiency and production efficiency. Use
data from Data Gallery #2 to support your answer. Answer in no more than two sentences.
FIGURE 27.23 shows budgets for two species in a saltmarsh food web. After eating, the food is either
assimilated into the body via the digestive system, or eliminated as feces. Assimilation efficiency is then
the proportion of food consumed that is assimilated into the body (assimilation/consumption).
Production efficiency is production/assimilation, equal to the proportion of assimilated food that is
turned into biomass, rather used for respiration.
36. (CH27) Answer the following questions regarding energy flow and interactions in ecological
systems. Answer each in no more than two sentences.
a. Describe energy flow differences in the two food webs shown below.
There are three trophic levels in the Washington State rocky intertidal food web and five in the Gulf of
California rocky intertidal food web. The Washington State food web contained 11 species, 18.2% of
which were carnivores, and the Gulf of California food web contained 45 species, 15.6% of which were
carnivores (FIGURES 27.15 and 27.16). Fewer species leads to fewer pathways for energy to flow and
fewer trophic levels. Generalist predators like Pisaster and Heliaster can even prey upon other
predators, leading to more complex pathways.
Figure 27.15
Figure 27.16
Table 27.2
b. What does it tell you that >95% of possible interactions between species in a food web have
an actual interaction strength of 0?
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Most species do not interact with one another, or at least not in a predator-prey fashion.
c. What do very weak interactions, on the order of 1 x 10-7 (-7 on log scale) mean in terms of
energy flow?
These interactions are not that important in terms of energy flow and simply mean a predator rarely
consumes that prey.
Figure 27.17
d. What are the implications to energy flow if a top predator that interacts strongly with its prey
is eliminated from an ecological system, especially in two-link food chains with high
interaction strength in both links?
If a top predator is eliminated a trophic cascade may result. If both links are strong this could even more
strongly lead to a trophic cascade, although if there are alternate pathways provided by omnivory,
energy may flow through these pathways reducing the potential for a trophic cascade.
Figure 27.18B and C
37. (CH27) Using the data in the energy flow diagram below, answer the following questions:
a. Consider tertiary consumers. What percentage of energy available to them is assimilated
(show work)?
There is 67 Calories available to them, and they assimilate 21 Calories
(gross production includes biomass and respiration, whereas net
production is what’s left after respiration. 21/67 * 100 = 31.3%
b. What percentage of energy available to them is turned into
biomass (show work)?
Here it is 6/67 * 100 = 9.0%
c. What percentage of net primary production is turned into net
production of tertiary consumers (show work)?
NPP = 8,863 and net production of tertiary consumers is 6, so 6/8863 * 100 = 0.068%
d. What happens to the energy that goes into the “downstream export and decay” pathway?
That energy includes leaves, feces, carcasses, and it is consumed by decomposers and scavengers.
e. What happens to the energy that goes into the “respiration” pathway?
That energy is given off as heat and escapes into the environment.