Ecology

Geology/Geography/Oceanography/Atmospheric Sciences

Quiz 6 :

Water Relations

Quiz 6 :

Water Relations

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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 should natural selection on predator and prey populations have on the height of the curves?
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A functional response can be defined as the relationship between the animal and the food source available. The three types of functional responses are as follows:
• Type I:
The feeding rate increases linearly with the increase in food density. This is because of the less time taken by animals belonging to this group in finding the food source and handling the food. The animals can be both herbivores and carnivores that find and handle their prey easily.
• Type II:
At a low food density, the increase in response to food available is linear. This increase also shows less time taken by the animal to find and handle the food in the initial low density of food. However, this linearity does not seem to be present as the source increases. Thus, these animals do not take much time to find and handle the prey at low density but the time increases at intermediate level of food density due to completion and prey defense.
• Type III:
The increase in the functional response is very slow as compared to type I and II when the food density is low. Later the curve shows improvement but soon becomes saturated.
The animals showing this type of relationship with the food density, take long time to find the food, remove unwanted parts like nuts or skin etc.
The three types of responses at low food density can be shown as follows:
img There are many natural prey defenses exhibited mainly by the prey of predators of type III. These are as follows:
• Hiding from vicinity, camouflage and coverage with fur or snow to hide.
• Running, swimming or flying away
• Display of aposematic colors by Mulllerian mimicry or Batesian mimicry.
These prey are selected by natural selection as per their capability of defense. This makes it difficult to find them. If such a situation increases, the curves of type I and type II would deviate from linearity a take a sigmoid shape. The saturation point may show increased height which means, more time and food would be needed to reach it.. Type III may take a more curved sigmoid shape.
The natural election of better predators would probably make the sigmoid shape of the type III response linear as they are animals which take much of time to handle their prey. The type I and II would not be much affected. The height depends on the food resource availability so better predation may reduce it.
The net effect of the predator and prey population shows the three types of curves. However if the prey population decreases, type I and II won't show a linear increase. Also if the population of predators increases, the increase in the completion would make the curves more curved rather than linear. Type III would become linear if prey increases but decrease would make the sigmoid deeper.

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Can samples drawn from two different populations have approximately the same mean (e.g., body weight) yet have different variances? Why?
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The mean is defined as the average of the given samples of a data set. This value depends upon the number of samples in a given set and also the sum of the values of all the samples present.
Variance is the distribution of the sample and the differences of the samples from the mean value. Any two samples can have the same mean but different variances. The reason can be as follows:
• The variation is calculated by the standard deviation, and it is not the same as the calculation of the mean. The formulas vary, and the mean cannot be the representative of any variation.
• The two different samples can have the same mean, but the range can be different. One can have a very small range and one can have a very large range. Also, a greater range shows that the variation can be more.
• The mean does not denote the sample size. Hence two samples with the same mean can have a different sample size. On the other hand, this difference in the sample size would lead to variation.
Samples having the same mean have differed in variances. This statement can be shown using the following example:
Let us consider two samples that show the body weights of new born puppies.
Sample A: 5, 6, 4, 10, 12, 14, 18
Sample B: 5, 3, 9, 12, 14, 16
Mean of sample A:
img (approximately 10)
Mean of sample B:
img (approximately 10)
Let us calculate the standard deviation of each sample.
Sample A is shown in the following table:
img Therefore, we have
img Sample B is shown in the following table:
img Thus, we have
img Sample A and sample B have the same mean, but they show a difference in the standard deviation, which is a measure of variation.
Thus, two samples showing similarity in the mean can differ in their variances measurement.

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In chapter 6, we emphasized how the C 4 photosynthetic pathway saves water, but some researchers suggest that the greatest advantage of C 4 over C 3 plants occurs when CO 2 concentrations are low. What is the advantage of the C 4 pathway when CO 2 concentrations are low? As we shall see in chapter 23, the atmospheric concentration of CO 2 has been increasing for the last century or so. If this trend continues, and if the interactions between C 4 and C 3 plants are influenced by atmospheric CO 2 concentrations, how might the geographic distributions of C 3 and C 4 plants change?
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As per the favorable conditions required for the C 3 plants, CO 2 is an important factor. Thus, 200 ppm or more is the required concentration of carbon dioxide in the atmosphere for the survival of C 3 plants. On the other hand, C 4 plants can survive in a smaller concentration of carbon dioxide. C 4 plants lose less water, as they open a smaller amount of stomata at a time for this purpose. Thus, carbon dioxide is considered as a heat-trapping green house gas, and an increase in carbon dioxide would directly increase the atmospheric temperature. The increased temperature does not favor C 3 plants, so this would affect their photosynthetic ability.
When the atmospheric temperature increases, the water in the atmosphere is evaporated and the climate becomes dry. This results in increased transpiration, and soon the plant loses its water content up to a great extent. As a result, the stomata are closed in order to shut down the water loss. The water loss in C 3 plants is about 380-900 g of tissue produced. This leads to blockage in carbon dioxide uptake, as the stomatal opening is the only route. Both C 3 pathways and photosynthesis are shut down as a consequence.
This does not happen in C 4 plants, as they absorb sufficient carbon dioxide by opening fewer stomata. Hence, the loss of water is only 250-300 g per gram of tissue produced.
The following advantages are catered by C 4 plants when the carbon dioxide concentrations are low:
• C 4 plants avoid photorespiration, which is mediated by Rubisco and leads to the loss of carbon. This usually happens in C 3 plants when an increased temperature leads to stomatal closing and the scarcity of carbon dioxide, but such a process is completely avoided in C4 plants.
• Carbon dioxide is fixed in the regions of the leaf, where it occurs in high concentrations. This is done during the availability. Later, this carbon dioxide is converted to oxaloacetate in the cytoplasm. Hence, the scarcity doesn't stop the reaction.
If the increase in carbon dioxide in the atmosphere gradually progresses, the day would not be far when carbon dioxide concentration would increase far more than the tolerable amount by plants. This type of change in the environment would reduce the number of C 3 plants, and C 4 plants would increase in number. The reason for this would be the adaptation in C 4 plants for survival for increased carbon dioxide, which would be accompanied by a temperature increase, as carbon dioxide is a greenhouse gas.

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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? (Photosynthetic bacteria tap into the near infrared range.)
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The data of Iriarte and colleagues (1990) suggest that prey size may favor a particular body size among pumas (see fig. 6.16). 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 interpreted as the result of selection for efficient temperature regulation. Homeothermic animals are often larger at high latitudes, a pattern called Bergmann's rule. Larger animals, with lower surface area relative to their mass, would be theoretically better at conserving heat. Smaller animals, with higher surface area relative to their mass, would be theoretically better at keeping cool. So what determines predator size? Is predator size determined by climate, predator prey interactions, or both? Design a study of the influence of the environment on the size of homeothermic predators.
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Design a planetary ecosystem based entirely on chemosynthesis. You might choose an undiscovered planet of some distant star or one of the planets in our own solar system, either today or at some distant time in the past or future.
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How is plant allocation to roots versus shoots similar to plant regulation of temperature and water? (We discussed these topics in chapters 4 and 5.) Consider discussing these processes under the more general heading of homeostasis. (Homeostasis is the maintenance of a relatively constant internal environment.)
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The rivers of central Portugal have been invaded, and densely populated, by the Louisiana crayfish, Procambarus clarki, which looks like a freshwater lobster about 12 to 14 cm long. The otters of these rivers, which were studied by Graça and Ferrand de Almeida (1983), can easily catch and subdue these crayfish. Using the model for prey choice: img explain why the diets of the otters of central Portugal would shift from the highly diverse menu shown in figure 6.15, which included fish, frogs, water snakes, birds, and insects, to a diet dominated by crayfish. For the crayfish, assume low handling time, very high encounter rates, and high energy content.
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What are the relative advantages and disadvantages of being an herbivore, detritivore, or 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?
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In what kinds of environments would you expect to find the greatest predominance of C 3 , C 4 , or CAM plants? How can you explain the co-occurrence of two, or even all three, of these types of plants in one area? (Think about the variations in microclimate that we considered in chapters 4 and 5.)
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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 the mimic?
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Why do the standard deviation and variance generally represent variation in a sample better than the range?
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