Ecology

Geology/Geography/Oceanography/Atmospheric Sciences

Quiz 2 :

Life on Land

Quiz 2 :

Life on Land

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Use what you know about atmospheric circulation and seasonal changes in the sun's orientation to earth to explain the highly seasonal rainfall in the tropical dry forest and tropical savanna biomes. (Hint: Why does the rainy season in these biomes come during the warmer months?)
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Savanna biomes have two distinct seasons; winter and summer. These seasons are however, accompanied by the extreme rise and fall in temperature associated with these seasonal distinctions. The rainy season in the biome occurs during the summer season while the winter remains dry.
The topical dry forests are generally warm all round the year. There are alternating dry and wet seasons. Dry seasons last longer, while the rainy season is shorter than the dry season.
The seasonality in the rainfall of these two biomes is caused due to the shifts in the latitude at which the sun is directly overhead. As the earth revolves around the sun, this shift in the latitude occurs approximately between 23.5°N and 23.5°S. This shift in the latitudes is responsible for the generation of tropical storms.
In the tropical Savanna and the tropical dry forest biomes, the wet season occurs during the warm months of the year, which is the time during which the sun is almost overhead in these regions.

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Daniel Janzen (1981a, 1981b) proposed that the seeds of the guanacaste tree were once dispersed by several species of large mammals that became extinct following the end of the Pleistocene about 10,000 years ago. There may have been other plant species with a similar relationship with large herbivorous mammals. How do you think the distributions of these plant species may have changed from the time of the extinctions of Pleistocene mammals until the introduction of other large herbivores such as horses? How might the introduction of horses about 500 years ago have affected the distribution of these species? How could you test your ideas?
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Daniel Jansen's study of the guanacaste tree led him to the conclusion that the dispersion of the seeds of the tree was carried out by the large herbivorous animals including ground sloths, camels and horses following the end of Pleistocene about 10000 years ago. However, these animals became extinct probably due to over hunting by humans.
As a result, for thousands of years, the seeds produced by the guanacaste tree were not dispersed effectively in the absence of the dispersers. However, it continued to produce a large number of fruits. This led to the significant reduction in the number of Guanacaste trees in the region.
There would have been numerous other plants which were dependant on these large herbivorous animals for the dispersal of their seeds. After the extinction of these animal species, these trees too would have suffered low dispersal leading to an adverse effect on the plant population size. Some of them may also have got extinct.
However, many of these plant species survived, like the guanacaste tree. This fact suggests that some alternative mechanisms of seed dispersal may have existed or alternative dispersers may have done the job of seed dispersal for these trees.
Alternative means of the seed dispersal could be through multiple different vectors such as rodents and the other small animals. Also, the plants would have had to depend more on abiotic factors such as wind and rain for seed dispersal. Some trees are known to have evolved special structures on their fruits. Some examples of such structures are long and curved outgrowths which can easily cling on to animal feet and body parts. Hence, they get dispersed with the moving animals.

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If you measured the heights of 100 seedlings randomly drawn from the hypothetical population, instead of the 11 measured in the example, would the sample mean be likely to be exactly 5.7 cm?
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Would the mean height of a sample of 100 seedlings likely be closer to the true population mean than the mean of a sample of 11?
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Describe global patterns of atmospheric heating and circulation. What mechanisms produce high precipitation in the tropics? What mechanisms produce high precipitation at temperate latitudes? What mechanisms produce low precipitation in the tropics?
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English and other European languages have terms for four seasons: spring, summer, autumn, and winter. This vocabulary summarizes much of the annual climatic variation at midlatitudes in temperate regions. Are these four seasons useful for summarizing annual climatic changes across the rest of the globe? Look back at the climate diagrams presented in this chapter. How many seasons would you propose for each of these environments? What would you call these seasons?
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To date, which biomes have been the most heavily affected by humans? Which seem to be the most lightly affected? How would you assess human impact? How might these patterns change during this century? (You may need to consult the discussion of human population growth in the Applications section of chapter 11).
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We focused much of our discussion of biomes on their latitudinal distribution. The reasonably predictable relationship between latitude and temperature and precipitation provides a link between latitude and biomes. What other geographic variable might affect the distribution of temperature and precipitation and, therefore, of biomes?
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Draw a typical soil profile, indicating the principal layers, or horizons. Describe the characteristics of each layer.
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You probably suggested altitude in response to question 5 because of its important influence on climate. Some of the earliest studies of the geographic distribution of vegetation suggested a direct correspondence between latitudinal and altitudinal variation in climate, and our discussion in this chapter stressed the similarities in climatic changes with altitude and latitude. Now, what are some major climatic differences between high altitude at midlatitudes and high altitude at high latitudes?
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Biologists have observed much more similarity in species composition among boreal forests and among areas of tundra in Eurasia and North America than among tropical rain forests or among Mediterranean woodlands around the globe. Can you offer an explanation of this contrast based on the global distributions of these biomes shown in figures 2.10, 2.22, 2.31, and 2.34?
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How is the physical environment on mountains at midlatitudes similar to that in tropical alpine zones? How do these environments differ?
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