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Ecology Concepts and Applications 6th edition Manuel C. Molles - Solutions

According to the river continuum model, the organisms inhabiting headwater streams in temperate forest regions depend mainly upon organic material coming into the stream from the surrounding forests. According to the model, photosynthesis within the stream is only important in the downstream
How could you test the generalization that lake primary production and the composition of the biota living in lakes are strongly influenced by the availability of nutrients such as nitrogen and phosphorus? Assume that you have unlimited resources and that you have access to several experimental
Contrast the approaches of Charles Darwin and Gregor Mendel to the study of populations. What were Darwin's main discoveries? What were Mendel's main discoveries? How did the studies of Darwin and Mendel prepare the way for the later studies reviewed in chapter 4?
How did the studies of Douglas and Brunner complement the earlier studies of Clausen, Keck, and Hiesey?
What is the Hardy-Weinberg principle? What is Hardy-Weinberg equilibrium? What conditions are required for Hardy-Weinberg equilibrium?
Review the Hardy-Weinberg equilibrium equation. What parts of the equation represent gene frequencies? What elements represent genotype frequencies and phenotype frequencies? Are genotype and phenotype frequencies always the same? Use a hypothetical population to specify alleles and allelic
What is genetic drift? Under what circumstances do you expect genetic drift to occur? Under what circumstances is genetic drift unlikely to be important? Does genetic drift increase or decrease genetic variation in populations?
How might the distribution of beak sizes in the population differ from that shown in figure 4.13, if mate choice in the population was random with respect to beak size?
How did the studies of Scott Carroll and his colleagues demonstrate rapid evolutionary adaptation to introduced soapberry plants? What advantages do a group of organisms, such as soapberry bugs, offer to researchers studying natural selection compared to larger organisms such as Chihuahua spruce?
How do classical approaches to genetic studies, such as common garden experiments, and modern molecular techniques, such as DNA sequencing, complement each other? What are the advantages and disadvantages of each?
In most of the examples discussed in chapter 5, 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
Imagine a desert beetle that uses behavior to regulate its body temperature above 35°C. How might this beetle's use of microclimates created by shrubs, burrows, and bare ground change with the season?
J. L. Mosser and colleagues (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
The Applications 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
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
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.
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 were to design a tiger beetle that could best cope with thermal conditions on black beaches (see fig. 5.4), what color would it be? The
Distinguish among vapor pressure deficit, osmotic pressure, and water potential. How can all three phenomena be expressed in the same units of measure: pascals?
Leaf water potential is typically highest just before dawn and then decreases progressively through midday. Should lower leaf water potentials at midday increase or decrease the rate of water movement from soil to a plant? Assume soil water potential is approximately the same in early morning and
Compare the water budgets of the tenebrionid beetle, Onymacris, and the kangaroo rat, Dipodomys, shown in figures 6.9 and 6.10. Which of these two species obtains most of its water from metabolic water? Which relies most on condensation of fog as a water source? In which species do you see greater
In this chapter, we discussed water relations of tenebrionid beetles from the Namib Desert. However, members of this family also occur in moist temperate environments. How should water loss rates vary among species of tenebrionids from different environments? On what assumptions do you base your
Review water and salt regulation by marine and fresh water bony fish. Which of the two is hypoosmotic relative to its environment? Which of the two is hyperosmotic relative to its environment? Some sharks live in freshwater. How should the kidneys of marine and freshwater sharks function?
Why don't plants use highly energetic ultraviolet light for photosynthesis? Would it be impossible to evolve a photosynthetic system that uses ultraviolet light? Does the fact that many insects see ultraviolet light change your mind? Would it be possible to use infrared light for photosynthesis?
How is plant allocation to roots versus shoots similar to plant regulation of temperature and water? (We discussed these topics in chapters 5 and 6.) Consider discussing these processes under the more general heading of homeostasis.
In what kinds of environments would you expect to find the greatest predominance of C3, C4, or CAM plants? How can you explain the co-occurrence of two, or even all three, of these types of plants in one area?
In chapter 7, we emphasized how the C4 photosynthetic pathway saves water, but some researchers suggest that the greatest advantage of C4 over C3 plants occurs when CO2 concentrations are low. What is the advantage of the C4 pathway when CO2 concentrations are low? As we shall see in chapter 23,
In chapter 7, we emphasized how the C4 photosynthetic pathway saves water, but some researchers suggest that the greatest advantage of C4 over C3 plants occurs when CO2 concentrations are low. What is the advantage of the C4 pathway when CO2 concentrations are low? As we shall see in chapter 23,
What are the relative advantages and disadvantages of being an herbivore, a detritivore, or a carnivore? What kinds of organisms were left out of our discussions of herbivores, detritivores, and carnivores? Where do parasites fit? Where does Homo sapiens fit?
What advantage does advertising give to noxious prey? How would convergence in aposematic coloration among several species of Müllerian mimics contribute to the fitness of individuals in each species? In the case of Batesian mimicry, what are the costs and benefits of mimicry to the model and to
What kinds of animals would you expect to have type 1, 2, or 3 functional responses? How should natural selection for better prey defense affect the height of functional response curves? How should natural selection for more effective predators affect the height of the curves? What net effect
The data of Iriarte and colleagues (1990) suggest that prey size may favor a particular body size among pumas (see fig. 7.19). However, this variation in body size also correlates well with latitude; the larger pumas live at high latitudes. Consequently, this variation in body size has been
The introduction to chapter 8 included sketches of the behavior and social systems of several fish species. Using the concepts that you have learned in this chapter, revisit those examples and predict the forms of sexual selection occurring in each species.
One of the basic assumptions of the material presented in chapter 8 is that the form of reproduction will exert substantial influence on social interactions within a species. How might interactions differ in populations that reproduce asexually versus ones that engage in sexual reproduction? How
Endler (1980) pointed out that though field observations are consistent with the hypothesis that predators may exert natural selection on guppy coloration, some other factors in the environment could be affecting variation in male color patterns among guppy populations. What other factors,
Endler set up two experiments, one in the greenhouse and one in the field. What were the advantages of the greenhouse experiments? What were the shortcomings of the greenhouse experiments? Endler also set up field experiments along the Aripo River. What were the advantages of the field experiments
Discuss the scorpionfly mating system. Pay particular attention to the potential roles of intersexual and intrasexual selection in scorpionflies.
The results of numerous studies indicate nonrandom mating among plants at least under some conditions. These results lead to questions concerning the biological mechanisms that produce these nonrandom matings. How might the maternal plant control or at least influence the paternity of her seeds?
The details of experimental design are critical for determining the success or failure of both field and laboratory experiments. Results often depend on some small details. For instance, why did Jennifer Jarvis wait 1 year after establishing her laboratory colony of naked mole rats before
Behavioral ecologists have argued that naked mole rats are eusocial. What are the major characteristics of eusociality and which of those characteristics are shared by naked mole rats?
What confines Encelia farinosa to upland slopes in the Mojave Desert? Why is it uncommon along desert washes, where it would have access to much more water? What may allow E. frutescens to persist along desert washes whereas E. farinosa cannot?
Spruce trees, members of the genus Picea, occur throughout the boreal forest and on mountains farther south. For example, spruce grow in the Rocky Mountains south from the heart of boreal forest all the way to the deserts of the southern United States and Mexico. How do you think they would be
How might the structure of the environment; for example, the distributions of different soil types and soil moisture, affect the patterns of distribution in plant populations? How should interactions among plants affect their distributions?
Suppose that in the near future, the fish crow population in North America declines because of habitat destruction. Now that you have reviewed the large-scale distribution and abundance of the fish crow (see fig. 9.15b), devise a conservation plan for the species that includes establishing
Use the empirical relationship between size and population density observed in the studies by Damuth (1981) (see fig. 9.19) and Peters and Wassenberg (1983) (see fig. 9.20) to answer the following: For a given body size, which generally has the higher population density, birds or mammals? On
Outline Rabinowitz's classification (1981) of rarity, which she based on size of geographic range, breadth of habitat tolerance, and population size. In her scheme, which combination of attributes makes a species least vulnerable to extinction? Which combination makes a species the most vulnerable?
Can the analyses by Damuth (1981) and by Peters and Wassenberg (1983) be combined with that of Rabinowitz (1981) to make predictions about the relationship of animal size to its relative rarity? What two attributes of rarity, as defined by Rabinowitz, are not included in the analyses by Damuth and
Compare cohort and static life tables. What are the main assumptions of each? In what situations or for what organisms would it be practical to use either?
Population ecologists have assumed that populations of species with very high reproductive rates, those with offspring sometimes numbering in the millions per female, must have a type III survivorship curve even though very few survivorship data exist for such species. Why is this a reasonable
Draw hypothetical age structures for growing, declining, and stable populations. Explain how the age structure of a population with highly episodic reproduction might be misinterpreted as indicating population decline. How might population ecologists avoid such misinterpretations?
Concept 10.5 says that we can use the information in life tables and fecundity schedules to estimate some characteristics of populations (R0, T, r). Why does Concept 10.5 use the word "estimate" rather than "calculate"? In putting together your answer, think about the population of P. drummondii
From a life table and a fecundity schedule, you can estimate the geometric rate of increase, λ, the average reproductive rate, R0, the generation time, T, and the per capita rate of increase, r. That is a lot of information about a population. What minimum information do you need to construct a
C. S. Holling (1959) observed predator numerical responses to changes in prey density. He attributed the numerical responses to changes in the reproductive rates of the predators. Discuss a hypothetical example of reproductive-rate numerical response by a population of predators in terms of changes
For what types of organisms is the geometric model of population growth appropriate? For what types of organisms is the exponential model of population growth appropriate? In what circumstances would a population grow exponentially? In what circumstances would a population not grow exponentially?
While populations of gray and blue whales have grown rapidly, the North Atlantic right whale population remains dangerously small despite many decades of complete protection. Assuming that differences in population growth rates are determined by whale life histories and not by external factors such
How do you build the logistic model for population growth from the exponential model? What part of the logistic growth equation produces the sigmoidal growth curve?
In question 3, you thought about how the logistic growth equation produces a sigmoidal growth curve. Now, let's think about nature. What is it about the natural environment that produces sigmoidal growth? Pick a real organism living in an environment with which you are familiar and list the things
What is the relationship between per capita rate of increase, r, and the intrinsic rate of increase, rmax? In chapter 10, we estimated r from the life tables and fecundity schedules of two species. How would you estimate rmax?
Population biologists may refer to abiotic factors, such as temperature and moisture, as density-independent because such factors can affect population processes independently of local population density. At the same time, biotic factors, such as disease and competition, are called
Where on earth is human population density highest? Where is it lowest? Where on earth do no people live? Where are human populations growing the fastest? Where are they approximately stable?
What factors will determine the earth's carrying capacity for Homo sapiens? Explain why the earth's long-term (thousands of years) carrying capacity for the human population may be much lower than the projected population size for the year 2050. Now argue the other side. Explain how the numbers
The discussion of seed size and number focused mainly on the advantages associated with large seeds. However, research by Westoby, Leishman, and Lord has revealed that the plants from widely separated geographic regions produce a wide variety of seed sizes. If this variation is to be maintained,
Under what conditions should natural selection favor production of many small offspring versus the production of a few well provisioned offspring?
Plant ecologists using experimental studies have verified that seedlings growing from larger seeds have a better chance of surviving environmental challenges such as deep shade, drought, physical injury, and competition from other plants. Explain how growing from larger seeds could give an
The studies by Shine and Charnov (1992) and Gunderson (1997) addressed important questions of concern to life history ecologists and their work provided robust answers to those questions. However, the methods they employed differed substantially from those used in most of the studies discussed in
Grime's proposed classification of environments based on intensity of disturbance and stress resulted in four environments, three of which he proposed were inhabitable by plants and one of which was not. That fourth environment shows high intensity of disturbance and high stress. What sorts of life
Using what you know about the trade-off between seed number and seed size (e.g., fig. 12.7) and patterns of variation among plants, predict the relative number of seeds produced by the various plant growth forms and dispersal strategies listed in figure 12.8?
Apply Winemiller's model to plants. If you were to construct a strictly quantitative classification of plant life histories using Winemiller and Rose's approach, what information would you need about the plants included in your analysis? How many plant species would you need to have an idea of how
Design a greenhouse (glasshouse) experiment to test for intraspecific competition within a population of herbaceous plants. Specify the species of plant, the volume (or size of pot) and source of soil, the potentially limiting resource you will focus on (e.g., Tilman and Cowan [1989] studied
One of the conclusions that seems justified in light of several decades of studies of interspecific competition is that competition is a common and strong force operating in nature, but not always and not everywhere. List the environmental circumstances in which you think intraspecific and
How can the results of greenhouse experiments on competition help us understand the importance of competition among natural populations? How can a researcher enhance the correspondence of results between greenhouse experiments and the field situation?
Explain how self-thinning in field populations of plants can be used to support the hypothesis that intraspecific competition is a common occurrence among natural plant populations.
Researchers have characterized the niches of Darwin's finches by beak size (which correlates with diet) and the niches of salt marsh grasses by position in the intertidal zone. How would you characterize the niches of sympatric canid species such as red fox, coyote, and wolf in North America? Or
Explain why species that overlap a great deal in their fundamental niches have a high probability of competing. Now explain why species that overlap a great deal in their realized niches and live in the same area probably do not compete significantly
How was the amount of food that Gause (1934) provided in his experiment on competition among paramecia related to carrying capacity? In Gause's experiments on competition, P. aurelia excluded P. caudatum faster when he provided half the amount of food than when he doubled the amount of food.
In his experiments on competition between T. confusum and T. castaneum, Park (1954) found that one species usually excluded the other species but that the outcome depended upon physical conditions. In which circumstances did T. confusum have the competitive advantage? In which circumstances did T.
Discuss how mathematical theory, laboratory models, and field experiments have contributed to our understanding of the ecology of competition. List the advantages and disadvantages of each approach.
Predation is one of the processes by which one organism exploits another. Others are herbivory, parasitism, and disease. What distinguishes each of these processes, including predation, from the others? We can justify discussing these varied processes under the heading of exploitative interactions
How are manipulation of host behavior by spiny-headed worms and manipulation of plant growth by the rust Puccinia monoica the same? How are they different? The details of these parasitic interactions are very different in many ways from the predatory behavior of lions on the savannas of Africa. How
Predation by one flour beetle species on another can be used as a potent means of interference competition. However, the predatory strategy seems to fail consistently in the presence of the protozoan parasite Adelina tribolii. Explain how the predatory strategy works in one environmental
Early work on exploitation focused a great deal of attention on predator-prey relations. However, parasites and pathogens represent a substantial part of the discussions in chapter 14. Is this representation by parasites and pathogens just the result of biased choices by the author or do you think
Explain the roles of food and predators in producing cycles of abundance in populations of snowshoe hare. Populations of many of the predators that feed on snowshoe hares also cycle substantially. Explain population cycles among these predator populations.
What contributions have laboratory and mathematical models made to our understanding of predator-prey population cycles? What are the shortcomings of these modeling approaches? What are their advantages?
List and briefly describe mutualistic relationships that seem to contribute to the ecological integrity of the biosphere.
Outline how the honeyguide-human mutualism could have evolved from an earlier mutualism between honeyguides and honey badgers. In many parts of Africa today, people have begun to abandon traditional honey gathering in favor of keeping domestic bees and have also begun to substitute refined sugars
What contributions do mycorrhizal fungi make to their plant partners? What do plants contribute in return for the services of mycorrhizal fungi? How did Hardie (1985) demonstrate that mycorrhizae improve the water balance of red clover? How do mycorrhizae improve the capacity of plants to take up
Explain how mycorrhizal fungi may have evolved from ancestors that were originally parasites of plant roots. Do any of Johnson's results (1993) indicate that present-day mycorrhizal fungi may act as parasites? Be specific.
Janzen (1985) encouraged ecologists to take a more experimental approach to the study of mutualistic relationships. Outline the details of Janzen's own experiments on the mutualistic relationship between swollen thorn acacias and ants.
Inouye and Taylor's study (1979) of the relationship between ants and the aspen sunflower, Helianthella quinquenervis, provides a reasonable representative of temperate ant-plant protection mutualisms. Compare this mutualism with that of the tropical mutualism between swollen thorn acacias and ants.
How are coral-centered mutualisms similar to plant-centered mutualisms? How are they different? The exchanges between mutualistic partners in both systems revolve around energy, nutrients, and protection. Is this an accident of the cases discussed or are these key factors in the lives of organisms?
Outline the benefits and costs identified by Keeler's (1981, 1985) cost-benefit model for facultative ant-plant mutualism. From what perspective does Keeler's model view this mutualism? From the perspective of plant or ant? What would be some of the costs and benefits to consider if the model were
How could you change the Lotka-Volterra model of competition we discussed in chapter 13 into a model of mutualism? Would the resulting model be a cost-benefit model or a population dynamic model?
What is the difference between a community and a population? What are some distinguishing properties of communities? What is a guild? Give examples. What is a plant life-form? Give examples.
Why do introduced predators possibly threaten the species diversity of a community such as Lake Victoria, while indigenous predators do not? Think in evolutionary timescales as you develop your answer to this question.
Suppose you are a biologist working for an international conservation organization concerned with studying and conserving biological diversity. On one of your assignments you are sent out to explore the local biotas of several regions. As part of your survey work, you are to take large quantitative
What are species richness and species evenness? How does each of these components of species diversity contribute to the value of the Shannon-Wiener diversity index (H')? How do species evenness and richness influence the form of rank-abundance curves?
Compare the "trophic" niches of warblers and diatoms as described by MacArthur (1958) and Tilman (1977). Why is it important that the ecologist be familiar with the niches of study organisms before exploring relationships between environmental complexity and species diversity?
Communities in different areas may be organized in different ways. For instance, C. Ralph (1985) found that in Patagonia in Argentina, as foliage height diversity increases, bird species diversity decreases. This result is exactly the opposite of the pattern observed by MacArthur (1958) and others
According to the intermediate disturbance hypothesis, both low and high levels of disturbance can reduce species diversity. Explain possible mechanisms producing this relationship. Include trade-offs between competitive and dispersal abilities in your discussion.
Humans have been living in the tropical rain forests of the New World for at least 11,000 years. During this period, disturbance by humans has been a part of these tropical rain forests. Use the intermediate disturbance hypothesis to explain how recent disturbances threaten the biological diversity
Winemiller (1990) deleted "weak" trophic links from one set of food webs that he described for fish communities in Venezuela (see fig. 17.3). What was his criterion for designating weak interactions? Earlier, Paine (1980) suggested that ecologists could learn something by focusing on "strong" links

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