Download Integrating Concepts in Biology II

Integrating Concepts in Biology II
Answer Key for Sample Exam covering Chs 19-21 on Evolution of populations/ecological systems
1. (CH19) Explain why the data shown below support the hypothesis that flower color is being
selected for in the plant “desert snow.” Elaborate in no more than 3 sentences and support using
the data in the figures.
Flower color changes across the ravine, quite dramatically. None of the other four genetic loci (those
not associated with flower color) change across the ravine, as evidenced by the frequency of the most
common allozyme of each, suggesting no selection at those loci. The figure on the right shows that
white plants on the white side of the ravine, at least in one year, have higher reproduction than blue
plants on the white side, and in a different year the opposite was true. Even though there is variation
among years, this is still evidence of selection and may have led to the pattern seen in the left figure,
given enough time.
2. (CH19) Use data from Data Gallery #1 to explain how natural populations contain both drab and
bright guppy males. Limit your answers to a maximum of 4 sentences.
Figure 19.3A: drab males inspect less when females are present, suggesting they hang back with the
females. Figure 19.4: Females choose bold males no matter their coloration and there is not a perfect
correspondence between boldness and color (FIGURE 19.3B).
3. (CH19) Use data from Data Gallery #1 to explain why someone could logically predict that only
drab males would survive in a wild population. Limit your answers to a maximum of 2 sentences.
Figure 19.1 shows that timid (which is correlated with drab) fish survive longer.
4. (CH19) Does boldness depend on presence of females? What evidence do you use to support
your conclusion? Use data from Data Gallery #1 to support your answer.
In the presence of female guppies, bright guppies are more likely than drab guppies to swim toward and
inspect potential predators and bright guppies tend to be more bold (FIGURE 19.3).
5. (CH19) Why do drab males inspect as much as bright males in the absence of females? Use data
from Data Gallery #1 to support your answer.
Drab males spent less time inspecting predators when females were present, because they spent more
time near those females (FIGURE 19.3). These males may be more bold because they are paired with
another male.
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6. (CH19) Is boldness correlated with color? What is your evidence, and what can you conclude
about the strength of the relationship? Use data from Data Gallery #1 to support your answer.
FIGURE 19.3B shows a strong correlation between color index and inspection frequency. While there is a
fair amount of scatter in the relationship, the P-value < 0.005, indicating a significant relationship.
7. (CH20) Of the two hypotheses constructed to explain the pattern of diversity in orchids, which is
better supported? Use Data Gallery #1 to choose the data testing each hypothesis and indicate
how each hypothesis is well or poorly supported by the available data. Answer in no more than 2
sentences for each hypothesis.
Living in trees hypothesis is better supported than pollinator specialization.
The pollinator specialization hypothesis predicts that diversity arose through the process of
specialization of pollinators. Subfamilies with higher numbers of species ought to have a lower mean
number of pollinators/orchid species. The figure shows that there is not a conclusive relationship
between the number of pollinator per species for a subfamily and the diversity of that subfamily.
Subfamily A had the fewest number of pollinators per species but also the lowest species diversity, while
subfamily E had a higher mean number of pollinators per species, and yet extremely high diversity. The
hypothesis that highly specific pollinators would lead to higher species diversity is poorly supported
(FIGURE 20.6).
The living in trees hypothesis predicts that the epiphytic condition of living in trees has led to diversity
through an adaptive radiation. That is, an ancestral orchid evolved to live above ground and that
allowed descendant species to further evolve to live in the wide variety of microhabitats that exist in the
trees. The figure above on the left shows that, both among orchids and non-orchid plants, there were
fewer genera with only 1 species per genus for tree-dwelling plants. There were several genera with
more than 300 species per genus among the tree-dwelling orchids compared to no genera with more
than 300 species for orchids on the ground. These data indicate that orchids living in trees have higher
species diversity, supporting the hypothesis. The figures on the right merely show that that there are
multiple microhabitats, some of which have more species, in the trees. It is not evidence for or against
the “living in trees leads to diversity” hypothesis (FIGURES 20.4 and 20.5).
8. (CH20) What might be the advantage to an epiphytic plant living in any one of the microhabitats
found on a large tree? What might be a disadvantage that prevents more species and individuals
from surviving in the microhabitat you chose? Use data from Data Gallery #1 to support your
answer.
Advantage of living further out or higher up in the tree is that the epiphyte can obtain more light
(FIGURE 20.4). Possessing adaptations that allow small plants to live in trees provides them with high
light conditions, as opposed to being small and living in the shade on the ground. Orchids and other
plants with this adaptation are able to compete successfully for light, which may be limiting in forests.
Although living at the very tops of trees might provide orchids with the highest light conditions, very few
species live there. The disadvantages caused by high wind conditions, extreme daily temperature
variations, and lack of support from weak branches may outweigh the advantages of high light.
However, living high enough to gather light but gaining protection through a strong attachment to
branches or trunks appears to be of benefit to individuals and their descendants.
9. (CH20) Discuss one mechanism by which mosquitoes have been shown to evolve resistance to
insecticides. Use Data Gallery #1 to choose the data that supports your answer. Explain the
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mechanism and how the data illustrate evolution of the mechanism in mosquitoes. Answer in no
more than 3 sentences.
There are two mechanisms that we discussed. One is the modification, through adaptation, of a
detoxification enzyme, and the other is modification, through adaptation, of a target site. TABLE 20.3
shows that Tanzanian mosquitoes are more resistant to DDT than Gambian mosquitoes. When
examined for the mechanism of resistance, it was found that some variants of the enzyme GST was
found in greater quantities in Tanzanian mosquitoes and that some of those variants were much more
active in breaking down DDT than those in the Gambian mosquitoes. This latter point is important in
concluding that evolution had occurred, and was probably caused by exposure to DDT (FIGURE 20.24).
TABLE 20.4 shows that a population of mosquitoes known to be resistant to permethrin had both
altered detoxification enzyme and altered target site. When the enzyme that breaks down permethrin
was inhibited by PBO, there was some increase in susceptibility to permethrin. However, that can’t be
the only mechanism here, as they did not become as susceptible as the susceptible population.
Permethrin and DDT have the same target site (but different detoxification enzymes break them down),
so demonstrating that permethrin-resistant mosquitoes were also resistant to DDT is strong evidence
that the target site has been modified.
10. (CH20) Are A. gambiae from Gambia more susceptible to DDT than A. gambiae from Tanzania?
What data support your conclusion? Use Data Gallery #1 to choose the data that supports your
answer.
TABLE 20.3 shows that Tanzanian mosquitoes are more resistant to DDT than Gambian mosquitoes. The
concentration that kills 50% or 90% of the population from Gambia is much lower than the
concentration that kills 50% or 90% of the Tanzanian population.
11. (CH19) Using data from Data Gallery #1, describe the evidence that evolution occurred in wild
mustard due to a change in the climate. Support your answer with data and elaborate in no more
than 3 sentences.
Focus on the data comparing plants from 1997 to those from 2004, especially in the plants from the wet
soil population. Those plants, when exposed to dry conditions in the experiment, flowered earlier and
had higher survival than their ancestral plants from 1997. During the drought between 2000 and 2004,
the plant population evolved. There was less of a response in the 04 to 97 comparison of plants from
the dry soil site, but it was still there. Plants growing there were already adapted to dry conditions, so
were pre-adapted to the drought. The changes were adaptations for surviving and reproducing in a
short wet season, and we also see that the changes are heritable. All this indicates that the drought
placed selective pressure on the plants, causing them to adapt through natural selection to survive and
reproduce in a dry climate (FIGURES 19.10 and 19.11 and TABLE 19.1).
DATA GALLERY #1
Figure 19.1
Figure 19.2
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Figure 19.3
Figure 19.4
Figure 20.1
Figure 20.2
Figure 20.3
Figure 20.5
Figure 20.4
Figure 20.6
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Table 20.3
Table 20.4
Figure 20.23
Figure 19.10
Figure 20.24
Figure 19.9
Figure 19.11
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Table 19.1
12. (CH20) What are the implications to susceptibility and resistance of differences in the mass of
each GST variant? Would you predict some variants to play a larger role in resistance than others,
and if so, which ones? Use Data Gallery #1 to choose the data that supports your answer.
Scientists discovered that the GST family of genes was responsible for conferring resistance to this
population of mosquitoes. In the Tanzanian population, there was a greater amount of almost every GST
enzyme, and some of those enzymes had much higher activity in the resistant than the susceptible
population. Exposure to toxic chemicals can lead to increased expression of genes, as is evident for
several variants, but the higher activity for the same variant in the Tanzanian population than the
Gambian population indicates a mutation changed the allele to one that detoxifies DDT faster and may
play a larger role in resistance (FIGURE 20.24).
13. (CH20) If the enzyme that detoxifies permethrin is inhibited by PBO, what would you expect to
observe in the permethrin w/ PBO treatment in Table 20.4? What do you conclude regarding the
mechanism of resistance in this population of permethrin-resistant mosquitoes? Use Data Gallery
#1 to choose the data that supports your answer.
There was evidence that PBO inhibition led to an increased rate of mortality and shorter time for 50% or
90% mortality, which suggested that the detoxification enzyme was inhibited (TABLE 20.4).
14. (CH19) Interpret the p-values for Part A of the Figure 19.4, explaining what the p-values mean
both statistically and biologically:
A p-value of 0.058 above the left pair of bars is above the cutoff of 0.05 used conventionally to reject a
null hypothesis of no difference, thus we must conclude that while there may be a trend towards
females choosing bright males that are simulated to be bold, we cannot conclude that females are
displaying a preference here. For the right two bars the p-value is <0.01, and so we can reject the null
hypothesis and conclude with pretty high confidence that females are selecting drab males when drab
males are simulated to be bold and when a predator is present.
15. (CH19) Using at least one of the figures below, discuss one consequence to genetic diversity for a
species that has widely distributed, isolated, numerous, or small populations. Elaborate in no
more than 2 sentences and support with data.
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Populations that are small and isolated have greater genetic distance as geographic distance (Fig. 19.20)
and as a consequence of that population structure, heterozygosity has decreased (Figs. 19.19 and 19.22)
and alleles may be lost (Fig. 19.22). In small, isolated populations, genetic diversity often decreases
through the processes of genetic drift or natural selection. Figures 19.19 and 19.20 are from the study of
small plants widely distributed in the Swiss Alps, and Figure 19.22 is from the black grouse populations
in Europe, where one population in the Netherlands has experienced a population bottleneck, in which
alleles were lost due to random chance during a population crash. Combine that with isolation from
other populations, and genetic diversity declines. The consequence of the types of population
structures seen here is that genetic diversity can be lost, and that can lead to other consequences.
Figure 19.19
Figure 19.22
Figure 19.20
16. (CH20) Compare the dates of existence of Paranthropus and Homo, using the horizontal widths of
the colored boxes in the evolutionary tree below, with the mammalian communities in Africa at 2
and 1.5 million years ago, shown in Figure 20.21. In what type of habitat was each of these
hominid species living? Incorporate one of the following two themes of the Evolution Big Idea:
Organisms can be linked by lines of descent from common ancestry, and natural selection is a
mechanism of evolution that accounts for adaptation, into your answer.
Based on fossil evidence, scientists hypothesize that Paranthropus evolved about 3 MYA, followed by
Homo around 2.5 MYA. The evolutionary tree shows that Paranthropus lived from approximately 2.8 to
1.3 million years ago (MYA), while Homo lived from 2.5 MYA to the present. Both coexisted for a period
of time, but Paranthropus species went extinct about 1.6 MYA. Around 2 MYA, when multiple hominid
species coexisted, the habitats in southern and eastern Africa included growing proportions of grazing
mammals and declining proportions of tree-dwelling and fruit-eating mammals. This is evidence that
the environment was changing from a more forested habitat to open grassland. If Paranthropus had
evolved to live in trees or in forests, then the changing environment could have caused their extinction.
Homo species might have lived in more open areas already, and when these habitats expanded as
conditions became drier, these hominid species would have been favored by natural selection. Thus, a
grassland environment likely favored Homo, as they survived and Paranthropus died off during this
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environmental transition. Natural selection acts as a mechanism of evolution, accounting for the
adaptations (such as bipedalism and large brain).
Figure 20.21
Figure 20.20
17. (CH19) Choose three different scales-of-distance examples that illustrate a single mechanism of
evolution that slows the rate of speciation. To get full credit, you must describe in general or
name the species and how each figure is connected to this mechanism. Use Data Gallery #2 to
choose the data that supports your answer. Limit your answers to a maximum of 2 sentences
each.
a. FIGURES 19.12 and 19.13: on the scale of 10s or 100s of meters this fungus can disperse to different
rotting logs. Gene flow is the mechanism that slows the rate of speciation.
b. FIGURE 19.17: on the scale of 10s of km this annual flowering plant can disperse to different
geographic areas. Gene flow is the mechanism that slows the rate of speciation.
c. FIGURE 19.18: on the scale of 1000s of km, European starlings can disperse across the country. Gene
flow is the mechanism that slows the rate of speciation.
18. (CH19) A loss of genetic diversity is a form of evolution. Use data from Data Gallery #2 to support
your answer.
a. Give one example of a bottleneck effect. Explain why bottlenecks reduce genetic diversity.
Support your answer with data. Limit your answer to a maximum of 2 sentences.
FIGURE 19.21 illustrates a bottleneck, where a population drops dramatically in abundance in a short
time period. A bottleneck can be a form of genetic drift, where alleles are randomly lost from a
population. TABLE 19.2 shows that genetic distance can be high when one population goes through a
bottleneck compared to populations that have not experienced a bottleneck. FIGURE 19.22 shows that
heterozygosity can be low and alleles can be lost in populations experiencing a bottleneck.
b. Give an example of random loss of genetic diversity that is not the consequence of natural
selection. Support your answer with data. Limit your answer to a maximum of 2 sentences.
TABLE 19.2 shows that genetic distance can be high when one population goes through a bottleneck
compared to populations that have not experienced a bottleneck. FIGURE 19.22 shows that
heterozygosity can be low and alleles can be lost in populations experiencing a bottleneck. While not
known to be subject to a bottleneck, the plant species in FIGURE 19.19 have low heterozygosity, and
these populations are small and isolated. While not known to be subject to a bottleneck, the plant
species in FIGURE 19.19 have low heterozygosity, and these populations are small and isolated.
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19. (CH19) How does a “bottleneck effect” contribute to evolution? Use one specific example, name
the mechanism of evolution, and support your example with at least two data sets. Use data from
Data Gallery #2 to support your answer. Limit your answers to a maximum of 4 sentences.
A bottleneck contributes to evolution by changing frequencies of alleles in a population, the definition of
biological evolution. FIGURE 19.21 illustrates a bottleneck, where a black grouse population drops
dramatically in abundance in a short time period. A bottleneck can be a form of genetic drift, where
alleles are randomly lost from a population. TABLE 19.2 shows that genetic distance can be high when
one population goes through a bottleneck compared to populations that have not experienced a
bottleneck. FIGURE 19.22 shows that heterozygosity can be low and alleles can be lost in populations
experiencing a bottleneck.
20. (CH19) Predict the genetic and evolutionary consequences for populations of plants that are
pollinated predominantly by bumble bees. Now predict the genetic and evolutionary
consequences for populations of plants that are pollinated predominantly by butterflies. Use data
from Data Gallery #2 to support your answer.
In populations where bumblebees are the primary pollinator, you might conclude that population
clusters would be small, both in numbers of individuals and area occupied. Bumble bees, once in a
flower patch, fly very short distances from flower to flower (FIGURES 19.15 and 19.16). When butterflies
are the pollinator, populations are predicted to be more spread out and to be more highly connected
genetically, because gene flow and mating between widely separated individuals would be much more
substantial due to higher flight distances between flower visits (FIGURES 19.15 and 19.16).
DATA GALLERY #2
Figure 19.13
Figure 19.12
Figure 19.18
Figure 19.19
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Figure 19.7
Figure 19.5
Figure 19.6
Figure 19.17
Figure 19.15
Figure 19.16
Figure 19.20
Table 19.2
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Figure 19.21
Figure 21.3
Figure 19.22
Figure 21.2
Figure 21.4
21. (CH21) What are two adaptations in yucca moths which may have been selected for by yucca
plants? Support your answer with data from Data Gallery #2 and elaborate in no more than 2
sentences per adaptation.
The adaptations that you identify must be adaptations that are beneficial to the plant. They would
probably also be beneficial to the moth, too, but you must discuss from the plant’s perspective.
Adaptations that are acceptable include the moth’s habit of pollinating after laying an egg (laying an egg
first as an adaptation is not acceptable). Pollinating after egg-laying is shown in the positive correlation
in the middle figures below – this positive correlation suggests that moths that lay more eggs also
pollinate more. This benefits the plant and the moth. It is beneficial to the yucca plant, which
ultimately produces more fruits and more viable offspring when pollinated with lots of pollen, especially
from other plants. Other adaptations include moths flying immediately after collecting pollen. That is
one that directly benefits the plant, as it helps prevents self-pollination and facilitates spreading of
pollen to other plants. Pollinating unvisited flowers more than visited flowers also benefits the plants,
as moths have a limited supply of pollen, so they would both benefit by pollinating only when necessary
(FIGURES 21.2-21.4).
22. (CH21) Coevolution is not uncommon, but it is difficult to document.
a. Give one example of diffuse coevolution and support your answer with data from Data
Galleries 2 or 3. Limit your answers to a maximum of 3 sentences.
TABLE 21.1 shows the changing nutritional value of fruits that are dispersed by birds. In both cases there
are multiple species involved and the trees as a group change the nutritional status of their fruits as the
seasons changes, reflecting what the birds need at certain times of the year (energy or water, e.g.).
b. Give one example of pairwise coevolution and support your answer with data from Data
Galleries 2 or 3. Limit your answers to a maximum of 3 sentences.
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There are a couple of choices here, including the yucca moth and yucca plant or newts and garter
snakes.
In most cases there is one or only a couple of species on each side of the interaction, although
sometimes several yucca moths will interact with one yucca plant species or several plant species may
interact with one or more yucca moth species. FIGURE 21.2 shows that moths have behaviors that
benefit the plant – they are likely to pollinate a flower if they detect it has not been visited by another
moth, for instance. They also have behaviors that benefit themselves – they lay an egg first, and often
only lay one egg and then leave without pollinating a flower (FIGURE 21.3). But if they lay multiple eggs
on a flower they often usually pollinate at least once. If they don’t possess pollen already there is a high
likelihood they will collect pollen and then once collected, will immediately leave (FIGURE 21.4). Large
pollen loads from non-self lead to higher fruit retention and germination frequency, relative to pollen
from self (FIGURES 21.5 and 21.6).
FIGURE 21.7: Snakes that consumed a newt and did not survive had lower resistance than snakes that
consumed a newt and survived. This would lead to natural selection against snakes with lower
resistance – coevolution in action, as newts in areas with populations of snakes that have higher
resistance, on average, might evolve to have higher levels of tetrodotoxin. Even when exposed to newts
from a population with generally higher levels of tetrodotoxin, some garter snakes ought to be able to
resist those higher levels, and some of those newts may have below average levels of tetrodotoxin.
Garter snakes with higher resistance could handle a much longer exposure to toxic newts and could
survive after eating a newt. For snakes that both consumed and rejected newts, recovery time seemed
to be a function of exposure time. The longer a snake was exposed to a newt, the longer it took to
recover from the exposure to tetrodotoxin.
23. (CH21) How does variation in resistance to tetrodotoxin affect the ability of garter snakes to
utilize rough-skinned newts as prey? Support your answer with data from Data Gallery #3 and
elaborate in no more than 2 sentences.
FIGURE 21.7: Snakes that consumed a newt and did not survive had lower resistance than snakes that
consumed a newt and survived. This would lead to natural selection against snakes with lower
resistance. Even when exposed to newts from a population with generally higher levels of tetrodotoxin,
some garter snakes ought to be able to resist those higher levels, and some of those newts may have
below average levels of tetrodotoxin. Garter snakes with higher resistance could handle a much longer
exposure to toxic newts and could survive after eating a newt. For snakes that both consumed and
rejected newts, recovery time seemed to be a function of exposure time. The longer a snake was
exposed to a newt, the longer it took to recover from the exposure to tetrodotoxin.
24. (CH21) Summarize why coral with algae is an example of mutualism and not pathology or
parasitism. How do endosymbiotic algae enter their coral hosts? Support your answer with data
from Data Gallery #3 and elaborate in no more than 3 sentences.
Coral are not born with their symbiotic algae. Coral larvae eat the algae, some of which move from the
digestive system to inside animal cells of their new hosts (Figure 21.9). The algae supply their animal
hosts with energy derived from photosynthesis. The coral animal captures microscopic prey with their
tentacles, and they share the consumed nutrients with their symbiotic algae. Algae are unicellular
photosynthesizers that capture sunlight for energy and contain a range of different pigments that
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provide them with many different colors (Figures 21.8D and 21.9F). The photosynthetic pigment called
chlorophyll fluoresces red when stimulated by UV light.
25. (CH21) Describe differences in the induction of photosynthesis response among plants. Explain
why understory shrubs responded the way they did and how it relates to light availability
patterns. Support with data from Data Gallery #3 and elaborate in no more than 3 sentences.
FIGURES 21.15 and 21.16: The amount of light available to the various rainforest plants affected their
response to the simulated pattern of light. The shrubs that live beneath trees in the forest understory
had a higher percent induction after being kept in the shade before being exposed to bright light flashes.
After 1 minute, these plants had achieved a higher percentage of their maximum photosynthesis rate
than the other plants. In addition, their efficiency of use of these light flashes was extremely high. These
are good adaptations for plants living mostly in the shade and exposed to brief, but frequent, flashes of
bright light throughout the day. These plants and the plants living in the forest edge had somewhat
similar responses as the time in low light increased (Figure 21.15B). The plant that lived in clearings did
not respond well to light flashes and would not be predicted to in the understory or in shady areas
because of its lower induction and light use efficiency. Plant distributions, or where plants are found, are
affected by the adaptations that plants have to the amount and pattern of light available.
26. (CH21) The best working hypothesis for global coral bleaching is increased water temperature.
Use one example of correlational data and one example of causal data that support the
hypothesis that warm water is causing coral bleaching. Support your answer with data from Data
Gallery #3 and elaborate in no more than 3 sentences.
a. correlation: Figure 21.11 is correlational data that show that warmer sea surface temperatures are
associated with higher percentages of bleached coral cells.
b. causal: TABLE 21.3 shows that algal symbionts have altered photosynthetic capacity when exposed
to different temperatures.
Data Gallery #3
Figure 21.8
Figure 21.9
Figure 21.10
Figure 21.11
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Figure 21.12
Figure 21.13
Table 21.3
Figure 21.14
Figure 21.15
Figure 21.16
Figure 21.17
Table 21.4
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Figure 21.18
Figure 21.19
Figure 21.20
Figure 21.21
Figure 21.22
Figure 21.7
Figure 20.16
Figure 20.18
Table 21.1
Figure 20.19
27. (CH20) Analyze the evolutionary tree and the pattern of presence and absence of the three
introns studied by Qui and colleagues. Which group is more closely related to land plants, green
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algae or red algae? Which group of bryophytes—liverworts, mosses, or hornworts—is most
closely related to the algae? What evidence did you use to come to your conclusion?
Figure 20.15
Green algae are more closely related to land plants as suggested by the closer branching of the green
algae lineage to the land plant lineages. Liverworts seem to be most closely related to algae, based not
only on the branching pattern of the evolutionary tree but also based on the intron pattern, which is the
same for both liverworts and algae.
28. (CH21) Populations must adapt to their environment as it changes. Support your answer to the
following with data from Data Gallery #3.
a. Give one example of plants that exhibit diffuse co-evolution. Support your answer with data.
Limit your answer to a maximum of 3 sentences.
Fruit trees may exhibit diffuse co-evolution with their bird dispersers. TABLE 21.1 shows the changing
nutritional value of fruits that are dispersed by birds. In both cases there are multiple species involved
and the trees as a group change the nutritional status of their fruits as the seasons changes, reflecting
what the birds need at certain times of the year (energy or water, e.g.).
b. Give one example of an animal species that has evolved adaptations to a habitat that
experiences frequent disturbances. Support your answer with data. Limit your answer to a
maximum of 2 sentences.
The two mussel species in FIGURES 21.21 and 21.22 have different strategies for dealing with
disturbances. The large, heavy California mussel release gametes throughout the year (FIGURE 21.20),
has a higher shell weight per shell length than the blue mussel, and this allows the California mussel to
live in a zone of the intertidal that is subject to more disturbance and predation. The large thick shell
makes it more difficult for starfish and snails to prey upon it and waves to break it apart.
Populations of blue mussels that live lower down in the intertidal zone are subject to more disturbance,
predation, and competition. But access to more food resources may allow them to grow faster when
submerged below the high tide. The blue mussel releases gametes once a year, spawning in the winter
and early spring, which may also be a strategy for living in this area of frequent disturbance; the larvae
may have a better chance of survival in the cooler winter and spring temperatures. Larvae settle on
unoccupied rocks in winter, and because they grow more quickly than the California mussel at equal
height above the tide, early on in development they have a good chance of maintaining themselves at
least until they can reproduce once.