Question: In chapter 17, we examined the influences

> Biological interactions may also affect lake systems. How does the recent history of the Great Lakes suggest that the kinds of species that inhabit a lake influence the nature of the lake environment and the composition of the biological community?

> 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 tha

> 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 stre

> How might oxygen concentration of interstitial water be related to the grain size of the sand or mud sediment? How might the oxygen concentrations of tide pools in sheltered bays compare to those on the shores of exposed headlands?

> 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?

> How might a history of exposure to wide environmental fluctuation affect the physiological tolerances of intertidal species compared to close relatives in sub tidal and oceanic environments? How might salinity tolerance vary among organisms living at dif

> Most examples of regional and latitudinal variation in species richness cited in this chapter have been terrestrial. Consider regional variation in marine biotas. Like birds on land, fish are one of the best-studied groups of marine organisms. Moyle and

> Ricklefs (1987) pointed out that many large-scale contrasts in species richness and composition cannot be explained by local processes such as competition and predation. Ricklefs proposed that differences in history and geography can leave a unique stamp

> Explain how speciation and extinction rates might be affected by the area of continents. What evidence is there to support your explanation? What does the influence of area on rates of extinction and speciation have to do with higher species richness in

> Review the major hypotheses proposed to explain the higher species richness of tropical regions compared to temperate and high-latitude regions. How are each of these hypotheses related to relative rates of speciation and extinction in tropical regions a

> Now, suppose you are going to study the bird communities on the islands shown below, which lie equal distances from the mainland but differ in area. According to the equilibrium model of island biogeography, what should be the relative rates of immigrati

> Suppose you are about to study the bird communities on the islands shown above, which are identical in area but lie at different distances from the mainland. According to the equilibrium model of island biogeography, which of the islands should experienc

> Diamond’s estimates (1969) of numbers of species immigrating and numbers that became extinct (six versus five) were virtually identical. Is this near equality in numbers of extinction and immigration consistent with the equilibrium mode

> We discussed how Diamond (1969) documented immigrations and extinctions on the California Channel Islands by comparing his censuses of the birds of the islands with the birds recorded over 50 years earlier. Disregarding the numbers for San Miguel and San

> Refer to figure 22.5, which MacArthur and Wilson (1963) used to show how isolation affects species richness on islands. Find a detailed map of the Pacific Ocean and locate New Guinea. Next locate as many of the “near,â

> 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

> The following data (corrected from Preston 1962a) give the area and number of bird species on islands in the West Indies: The numbers are expressed in two ways: as simple measurements and counts and as the logarithms of area and numbers of species. Use

> Succession seems to lead to predictable changes in community and ecosystem structure. Predict the characteristics of a frequently disturbed community/ecosystem versus a largely undisturbed community/ecosystem. What do your predictions suggest about a fut

> How do the activities of animals affect landscape heterogeneity? You might use either beaver or human activity as your model. What parallels can you think of between the influence of animal activity on landscape heterogeneity and the intermediate disturb

> Analyses such as Milne’s comparison (1993) of bald eagles and barnacles demonstrate that organisms of different sizes interact with the environment at very different spatial scales. With this in mind consider the experiments of Diffendo

> Use fractal geometry and the niche concept (see chapters 9, 13, and 16) to explain why the canopy of a forest should accommodate more species of predaceous insects than insectivorous birds. Assume that the numbers of bird and predaceous insect species ar

> How do the positions of patches in a landscape affect the movement of individuals among habitat patches and among portions of a metapopulation? Again, consider the hypothetical landscapes shown in question 5. Which of the two landscapes would promote the

> Consider the options for preserving patches of riverside forest shown in landscapes 3 and 4. Again, the two landscapes contain the same total area of forest but the patches in the two landscapes differ in shape. Which of the two would be most dominated b

> How do the positions of patches in a landscape affect the movement of individuals among habitat patches and among portions of a metapopulation? Again, consider the hypothetical landscapes shown in question 5. Which of the two landscapes would promote the

> The green areas represent forest fragments surrounded by agriculture. Landscapes 1 and 2 contain the same total forest area. Which landscape, 1 or 2, will contain more forest interior species? Explain. Landscape 1 Landscape 2

> How should the area of forest patches in an agricultural landscape affect the proportion of bird species in a community that are associated with forest edge habitats? How should patch area affect the presence of birds associated with forest interiors?

> 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? Figure 4.13: Higher rate of survival by birds with smal

> How does landscape ecology differ from ecosystem and community ecology? What questions might an ecosystem ecologist ask about a forest? What questions might a community ecologist ask about the same forest? Now, what kinds of questions would a landscape e

> Species have come and gone in response to changing global climates during the history of the earth. Some of the mass extinctions of the past have resulted in the deaths of over 90% of existing species. What do these biological changes suggest about the l

> Ecological succession has been compared to the development of an organism and the climax community to a kind of superorganism. F. E. Clements (1916, 1936) was the best-known proponent of this idea, and H. A. Gleason (1926, 1939), the best-known early opp

> When Mount St. Helens in Washington erupted in 1980, it created a gradient in disturbance. In the pumice plains near the eruption, the devastation was almost total. The extent of disturbance was much less in the farthest reaches of the blast zone. How mi

> In the studies of mechanisms underlying succession, ecologists have found a great deal of evidence for both facilitation and inhibition. However, they have found little evidence for the tolerance model. Explain this lack of support for the tolerance mode

> The rapid succession shown by the Sycamore Creek ecosystem is impressive. How might natural selection influence the life cycles of the organisms living in Sycamore Creek? Imagine a creek that floods about twice per century. How quickly would you expect t

> In most studies of forest succession such as that of Reiners and colleagues (1971) and Oosting (1942), researchers study succession by comparing sites of various ages. This approach is called a “space for time substitution.” What are some major assumptio

> The successional studies in Sycamore Creek produced patterns of variation in diversity that differed significantly from those observed during primary succession at Glacier Bay (see fig.  20.2), old field succession on the Piedmont

> Would you expect the number of species to remain indefinitely at the level shown in figure 20.7? Space on large, stable boulders in Sousa’s study site is dominated by the algal G. canaliculata and support 2.3 to 3.5 species,

> As we saw in figure  20.5, Johnston and Odum (1956) documented substantial change in the richness of bird species in a successional sequence going from the earliest stages in which the plant community was dominated by grasses and forbs to mat

> Suppose you are a director of a captive breeding program for a rare species of animal, such as Siberian tigers, which are found in many zoos around the world but are increasingly rare in the wild. Design a breeding program that will reduce the possibilit

> If rates of decomposition are higher in ecosystems with higher nutrient availability, how should nutrient enrichment affect rates of decomposition? Because of its effects on fungal diversity, could nutrient enrichment of ecosystems affect rates of decomp

> Kauffman and his colleagues (1993) estimated that burning the tropical forest at their study site resulted in the loss of approximately 21 kg per hectare of phosphorus. This quantity is about 11% to 17% of the total pool of phosphorus. If total annual in

> The fynbos of South Africa is famous for the exceptional diversity of its plant community. Witkowski (1991) showed that invading Acacia are enriching the fynbos soil with nitrogen. How might enriching soil nitrogen affect plant diversity in this ecosyste

> McNaughton, Ruess, and Seagle (1988) proposed that grazing by large mammals increases the rate of nitrogen cycling on the savannas of East Africa. Explain how passing through a large mammal could increase the rate of breakdown of plant biomass. In chapte

> Likens and Bormann (1995) found that vegetation substantially influences the rate of nutrient loss from small stream catchments in the northern hardwood forest ecosystem. How do vegetative biomass and rates of primary production in these forests affect t

> Many rivers around the world have been straightened and deepened to improve conditions for navigation. Side effects of these changes include increased average water velocity and decreased movement of water into shallow riverside environments such as eddi

> Melillo, Aber, and Muratore (1982) suggested that soil fertility may influence the rate of decomposition in terrestrial ecosystems. Design an experiment to test this hypothesis. If you test for the effects of soil fertility, how will you control for the

> Review figure 18.2, in which Rosenzweig (1968) plotted the relationship between actual evapotranspiration and net primary production. How do you think that decomposition rates change across the same ecosystems? Using what you learned in chapterÂ&nb

> Parmenter and Lamarra (1991) studied decomposition of fish and waterfowl carrion in a freshwater marsh. During the course of their studies they found that the soft tissues of both fish and waterfowl decomposed faster than the most rapidly decomposing pla

> Of all the naturally occurring elements in the biosphere, why have the cycles of carbon, nitrogen, and phosphorus been so intensively studied by ecologists? (Hint: Think about the kinds of organic molecules of which these elements are constituents. Also

> 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?

> In chapter 17, we examined the influences of keystone species on the structure of communities. In chapter 18, we reviewed trophic cascades. Discuss the similarities and differences between these two concepts. Compare the measurements and methods of ecolo

> Most of the energy that flows through a forest ecosystem flows through detritus-based food chains, and the detritus consists mainly of dead plant tissues (e.g., leaves and wood). In contrast, most of the energy flowing through a pelagic marine or freshwa

> Suppose you are studying a community of small mammals that live on the boundary between a riverside forest and a semidesert grassland. One of your concerns is to discover the relative contributions of the grassland and the forest to the nutrition of smal

> Compare the pictures of trophic structure that emerged from our discussions of food webs in chapter 17 with those in chapter 18. What are the strengths of each perspective? What are their limitations?

> Shaver and Chapin (1986) pointed out that though the tundra ecosystems they studied consistently increased primary production in response to fertilization, individual species and growth forms showed more variation in response. Some species and growth for

> Field experiments demonstrate that variation in soil fertility influences terrestrial primary production. However, we cannot say that nutrients exert primary control. That role is still attributed to temperature and moisture. Why do ecologists still attr

> Many migratory birds spend approximately half the year in temperate forests during the warm breeding season and the other half of the year in tropical forest. Given the analyses you made in question 2, which forest appears to be more productive from the

> M. Huston (1994b) pointed out that the well-documented pattern of increasing annual primary production from the poles to the equator is strongly influenced by the longer growing season at low latitudes. The following data are from table 14.10 in Huston.

> Population, community, and ecosystem ecologists study structure and process. However, they focus on different natural characteristics. Contrast the important structures and processes in a forest from the perspectives of population, community, and ecosyst

> 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 popu

> 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.

> 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 d

> The dams that have been built on many rivers often stabilize river flow by increasing flows below the dam during droughts and decreasing the amount of flooding during periods of high rainfall. Using the intermediate disturbance hypothesis, predict how st

> All the keystone species work we have discussed in chapter 17 has concerned the influences of animals on the structure of communities. Can other groups of organism’s act as keystones? What about parasites and pathogens?

> Some paleontologists have proposed that overhunting caused the extinction of many large North American mammals at the end of the Pleistocene about 11,000 and 10,000 years ago. The hunters implicated by paleontologists were a newly arrived predatory speci

> Using Tscharntke’s food web (1992) shown in figure 17.5, predict which species would be most affected if you excluded the bird at the top of the web, Parus caeruleus. What species would be affected less? Assume that P. caeru

> When Power (1990) excluded predaceous fish from her river sites, the density of herbivorous insect larvae (chironomids) decreased. Use the food web described by Power to explain this response.

> Explain how the experiments of Lubchenco (1978) showed that feeding preferences, population density, and competitive relations among food species all potentially contribute to the influences of “keystone” consumers on the structure of communities. What r

> What is a keystone species? Paine (1966, 1969) experimented with two sea stars that act as keystone species in their intertidal communities along the west coast of North America and in New Zealand. Describe how the intertidal communities in these two are

> 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? Earlie

> What is the Hardy-Weinberg principle? What is Hardy- Weinberg equilibrium? What conditions are required for Hardy-Weinberg equilibrium?

> 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 di

> 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 pat

> 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

> 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?

> 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 su

> How does feeding by urchins, which prey on young corals, improve establishment by young corals? Use a diagram outlining interactions among urchins, corals, and algae to help in the development of your explanation.

> 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.

> 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 h

> We included spatial refuges, predator satiation, and size in our discussions of the role played by refuges in the persistence of exploited species. How could time act as a refuge? Explain how natural selection could lead to the evolution of temporal “ref

> 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 cost

> How did the studies of Douglas and Brunner complement the earlier studies of Clausen, Keck, and Hiesey?

> 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

> 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 mut

> 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.

> 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.

> Outline the experiments of Johnson (1993), which she designed to test the possibility that artificial fertilizers may select for less mutualistic mycorrhizal fungi. What evidence does Johnson present in support of her hypothesis?

> 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 mycorrhiza

> List and briefly describe mutualistic relationships that seem to contribute to the ecological integrity of the biosphere.

> 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 circumstance

> 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?

> 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 population

> Review the distribution of water among the major reservoirs of the hydrologic cycle. What are the major sources of freshwater? Explain why according to some projections availability of freshwater may limit human populations and activity.

> Researchers have suggested that predators could actually increase the population density of a prey species heavily infected by a pathogenic parasite (Hudson, Dobson, and Newborn 1992). Explain how predation could lead to population increases in the prey

> 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

> In chapter 14 we have seen how a herbivorous stream insect controls the density of its food organisms, how a herbivorous moth larva and pathogenic microbes combine to control an introduced cactus population, and how decimation of a red fox population led

> 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 s

> 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 beh

> 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 un

> 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.

> 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 competit