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44.E: Ecology and the Biosphere (Exercises)

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    44.1: The Scope of Ecology

    Ecology is the study of the interactions of living organisms with their environment. One core goal of ecology is to understand the distribution and abundance of living things in the physical environment. Attainment of this goal requires the integration of scientific disciplines inside and outside of biology, such as biochemistry, physiology, evolution, biodiversity, molecular biology, geology, and climatology.

    Review Questions

    Which of the following is a biotic factor?

    1. wind
    2. disease-causing microbe
    3. temperature
    4. soil particle size


    The study of nutrient cycling though the environment is an example of which of the following?

    1. organismal ecology
    2. population ecology
    3. community ecology
    4. ecosystem ecology


    Free Response

    Ecologists often collaborate with other researchers interested in ecological questions. Describe the levels of ecology that would be easier for collaboration because of the similarities of questions asked. What levels of ecology might be more difficult for collaboration?

    Ecologists working in organismal or population ecology might ask similar questions about how the biotic and abiotic conditions affect particular organisms and, thus, might find collaboration to be mutually beneficial. Levels of ecology such as community ecology or ecosystem ecology might pose greater challenges for collaboration because these areas are very broad and may include many different environmental components.

    The population is an important unit in ecology as well as other biological sciences. How is a population defined, and what are the strengths and weaknesses of this definition? Are there some species that at certain times or places are not in populations?

    It is beneficial to consider a population to be all of the individuals living in the same area at the same time because it allows the ecologist to identify and study all of the abiotic and biotic factors that may affect the members of the population. However, this definition of a population could be considered a drawback if it prohibits the ecologist from studying a population’s individuals that may be transitory, but still influential. Some species with members that have a wide geographic range might not be considered to be a population, but could still have many of the qualities of a population.



    44.2: Biogeography

    Many forces influence the communities of living organisms present in different parts of the biosphere (all of the parts of Earth inhabited by life). The biosphere extends into the atmosphere (several kilometers above Earth) and into the depths of the oceans. Despite its apparent vastness to an individual human, the biosphere occupies only a minute space when compared to the known universe. Many abiotic forces influence where life can exist and the types of organisms found in the biosphere.

    Review Questions

    Understory plants in a temperate forest have adaptations to capture limited ________.

    1. water
    2. nutrients
    3. heat
    4. sunlight


    An ecologist hiking up a mountain may notice different biomes along the way due to changes in all of the following except:

    1. elevation
    2. rainfall
    3. latitude
    4. temperature


    Free Response

    Compare and contrast ocean upwelling and spring and fall turnovers.

    Ocean upwelling is a continual process that occurs year-round. Spring and fall turnover in freshwater lakes and ponds, however, is a seasonal process that occurs due to temperature changes in the water that take place during springtime warming and autumn cooling. Both ocean upwelling and spring and fall turnover enable nutrients in the organic materials at the bottom of the body of water to be recycled and reused by living things.

    Many endemic species are found in areas that are geographically isolated. Suggest a plausible scientific explanation for why this is so.

    Areas that have been geographically isolated for very long periods of time allow unique species to evolve; these species are distinctly different from those of surrounding areas and remain so, since geographic isolation keeps them separated from other species.



    44.3: Terrestrial Biomes

    The Earth’s biomes are categorized into two major groups: terrestrial and aquatic. Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes. The eight major terrestrial biomes on Earth are each distinguished by characteristic temperatures and amount of precipitation. Comparing the annual totals of precipitation and fluctuations in precipitation from one biome to another provides clues as to the importance of abiotic factors in the distribution of biomes

    Review Questions

    Which of the following biomes is characterized by abundant water resources?

    1. deserts
    2. boreal forests
    3. savannas
    4. tropical wet forests


    Which of the following biomes is characterized by short growing seasons?

    1. deserts
    2. tropical wet forests
    3. Arctic tundras
    4. savannas


    Free Response

    The extremely low precipitation of subtropical desert biomes might lead one to expect fire to be a major disturbance factor; however, fire is more common in the temperate grassland biome than in the subtropic desert biome. Why is this?

    Fire is less common in desert biomes than in temperate grasslands because deserts have low net primary productivity and, thus, very little plant biomass to fuel a fire.

    In what ways are the subtropical desert and the arctic tundra similar?

    Both the subtropical desert and the arctic tundra have a low supply of water. In the desert, this is due to extremely low precipitation, and in the arctic tundra, much of the water is unavailable to plants because it is frozen. Both the subtropical desert and the arctic tundra have low net primary productivity.



    44.4: Aquatic Biomes

    Like terrestrial biomes, aquatic biomes are influenced by a series of abiotic factors. The aquatic medium—water— has different physical and chemical properties than air, however. Even if the water in a pond or other body of water is perfectly clear (there are no suspended particles), water, on its own, absorbs light. As one descends into a deep body of water, there will eventually be a depth which the sunlight cannot reach.

    Review Questions

    Where would you expect to find the most photosynthesis in an ocean biome?

    1. aphotic zone
    2. abyssal zone
    3. benthic realm
    4. intertidal zone


    A key feature of estuaries is:

    1. low light conditions and high productivity
    2. salt water and fresh water
    3. frequent algal blooms
    4. little or no vegetation


    Free Response

    Scientists have discovered the bodies of humans and other living things buried in bogs for hundreds of years, but not yet decomposed. Suggest a possible biological explanation for why such bodies are so well-preserved.

    Bogs are low in oxygen and high in organic acids. The low oxygen content and the low pH both slow the rate of decomposition.

    Describe the conditions and challenges facing organisms living in the intertidal zone.

    Organisms living in the intertidal zone must tolerate periodic exposure to air and sunlight and must be able to be periodically dry. They also must be able to endure the pounding waves; for this reason, some shoreline organisms have hard exoskeletons that provide protection while also reducing the likelihood of drying out.



    44.5: Climate and the Effects of Global Climate Change

    All biomes are universally affected by global conditions, such as climate, that ultimately shape each biome’s environment. Scientists who study climate have noted a series of marked changes that have gradually become increasingly evident during the last sixty years. Global climate change is the term used to describe altered global weather patterns, including a worldwide increase in temperature, due largely to rising levels of atmospheric carbon dioxide.

    Review Questions

    Which of the following is an example of a weather event?

    1. The hurricane season lasts from June 1 through November 30.
    2. The amount of atmospheric CO2 has steadily increased during the last century.
    3. A windstorm blew down trees in the Boundary Waters Canoe Area in Minnesota on July 4, 1999.
    4. Deserts are generally dry ecosystems having very little rainfall.


    Which of the following natural forces is responsible for the release of carbon dioxide and other atmospheric gases?

    1. the Milankovitch cycles
    2. volcanoes
    3. solar intensity
    4. burning of fossil fuels


    Free Response

    Compare and contrast how natural- and human-induced processes have influenced global climate change.

    Natural processes such as the Milankovitch cycles, variation in solar intensity, and volcanic eruptions can cause periodic, intermittent changes in global climate. Human activity, in the form of emissions from the burning of fossil fuels, has caused a progressive rise in the levels of atmospheric carbon dioxide.

    Predict possible consequences if carbon emissions from fossil fuels continue to rise.

    If carbon emissions continue to rise, the global temperature will continue to rise; thus, ocean waters will cause the rising of sea levels at the coastlines. Continued melting of glaciers and reduced spring and summer meltwaters may cause summertime water shortages. Changes in seasonal temperatures may alter lifecycles and interrupt breeding patterns in many species of plants and animals.