Ecology

Geology/Geography/Oceanography/Atmospheric Sciences

Quiz 15 :

Mutualism

Quiz 15 :

Mutualism

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List and briefly describe mutualistic relationships that seem to contribute to the ecological integrity of the biosphere.
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Mutualism refers to a symbiotic association between two species, in which both the partners derive benefit from each other. Mutualism exists throughout the biosphere and it is an integral part of nature. Absence of mutualism in the biosphere would make it biologically impoverished.
There are several examples of the mutualisms that are essential to maintain life on earth. The elimination of even a few of them could bring life to a still. Some examples of the mutualisms that contribute to ecological integrity are described below.
1. Mutualism between plants and birds/animals:
In a plant bird mutualism, the bird receives nectar that is food for its survival. In turn, the bird performs the job of pollination for the plant. Birds, while feeding on the nectar of flowers, pick up the pollens and transfer them on to different flowers to bring about pollination. Pollination is essential for plants, as is feeding for the birds. In the absence of such a mutualism, pollination would become very difficult and eventually only the wind-pollinated plants would survive. The birds, butterflies, and bees would disappear.
2. Mycorrhizae:
It is an association between the plants and fungi. The fungal partner receives organic compounds required for growth and reproduction from the plant. The fungus greatly improves the accessibility of the plants to inorganic nutrients like phosphorous, nitrogen, copper, zinc, and most importantly water. This mutualism is also extremely important for the survival of plants. In the absence of mycorrhiza, plants would be restricted only to the most fertile soils on earth.
3. Mutualism between corals and algae:
Corals provide the shelter and inorganic nutrients like nitrogen, phosphorous and others to the algal partner, which in turn provide organic nutrients to the corals. This mutualism is responsible for the biological structures called coral reefs. In the absence of this association, we would not have seen Great Barrier Reef, the largest biological structure on earth. Absence of the coral reefs and other mutualisms between ocean species would lead to great loss of biodiversity in the oceans.
4. Mutualism between herbivorous animals and plants:
The plant material contains cellulose which cannot be digested alone by the animal's enzymes. The large number of protozoa and bacteria living in the gut of the animal produce enzymes that degrade cellulose for the animal. In turn, the microbes receive a steady food supply and a protective environment for survival and multiplication.

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What is the 95% confidence interval for the Gila River sample of loach minnows?
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A confidence interval is a range of values within which the true population mean occurs with a particular probability.
The level of confidence is calculated using the formula:
img Using this level of confidence produces what is called a 95% confidence interval which is calculated as follows:
img …… (1)
Given,
img Substituting the given values in equation (1)
img img Hence, the 95% confidence interval for the Gila River sample of loach minnows is
img

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What value of would you use from table A.1 for calculating a 95% confidence interval, if your sample size was 18 and your significance level was
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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 like parasites? Be specific.
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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?
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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?
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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.
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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 bought at the market for the honey of wild bees. Explain how, under these circumstances, natural selection might eliminate guiding behavior in populations of the greater honeyguide. (In areas where honey gathering is no longer practiced, the greater honeyguide no longer guides people to bees' nests.)
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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 water from their environment?
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How are the coral-centered mutualisms similar to the plantcentered mutualisms we discussed in chapter 15? 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?
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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.
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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 was built from the perspective of the other partner?
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