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Cycles of Life:
EXPLORING BIOLOGY
Module 7: Ecology
Segment 1: Populations
Objectives:
1. Identify population size as a characteristic of a population, which serves as a starting point for
the study of population biology.
2. Describe the shape of the idealized (J-shaped) growth curve of a population, possible only in the
absence of limiting factors.
3. Compare the idealized growth curve with the S-shaped (logistic) curve demonstrated by many
populations in nature.
4. Describe how density-dependent and density-independent controls determine and sometimes
modify an S-shaped growth curve.
Video Synopsis:
The Santa Ana Woolly Star is an unspectacular plant, but it’s an important part of the ecological
puzzle in maintaining the stability of its environment. We follow Dr. Jack Burk and his students as
they try to stabilize the environment of this endangered population. In this segment, we learn about
the characteristics of a population, and the factors that influence the growth or demise of a given
population.
Questions:
1. What is the role of the Woolly Star in its habitat? What organisms would be affected if it
died out?
• Grows in newly deposited loose sand, helping hold it in place so other species can move in.
• Provides food and shelter for insects, which support rodents, birds and larger predators. All
would be negatively affected without the Woolly Star.
2. Why is it important to monitor endangered species, and how are such populations studied
in the field?
• Need early warning of changes in the population to respond in time.
• Rare plants and animals are more sensitive to changes in the environment and are a good
“barometer” of habitat health.
3. What is a growth curve? What causes J- shaped and S- shaped curves to develop?
• A growth curve is a graphical representation of the rate of change in a population, i.e.,
number of individuals in a population plotted versus time.
• Both curves begin the same way, slow growth at first because so few organisms are present,
followed by more and more rapid growth. The organisms don’t do anything different to
cause the marked upswing, there are just more of them.
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The J-curve suddenly peaks (maximum) then crashes to zero (death phase). In nature, this
occurs before the environment causes resistance (no lack of food, etc.). The organisms have
a short life span; they are born, they reproduce, they die (mosquitoes, flies). No resistance is
needed.
The S-curve is much more common, especially for longer lived animals. When more
individuals live in an area for a longer period of time, the organisms start competing for food,
mates, homes, and waste recycling. These factors are called environmental resistance because
they “resist” continued growth. Growth levels out and population size is maintained at a
level called the “carrying capacity”.
4. What do J- and S-shaped population curves indicate about the lifespan of an organism?
• No population in nature can have a true J- shape that continues to skyrocket. Those said to
have this shape grow until they suddenly die off and population falls to zero, leaving only
fertile eggs to provide the next J-shaped generation. Usually such adult populations live less
than one season of one year, and sometimes only hours or days.
• S-curves have a long, stable population size. S-curves are most common and include
populations from mice to hawks and beyond. Outside influences may modify the carrying
capacity (eg. predators, drought, flood, etc.) but it will restabilize.
5. Name some density-dependent and density-independent factors that might affect S-shaped
growth curves.
• Density-dependent factors are made worse by increased population size (competition for
food, living space, waste disposal, and mates). Even sickness and disease often become worse
as crowding increases.
• Density-independent factors are often catastrophic (storms, floods, volcanoes, tornadoes,
etc.) but in the case of the Woolly Star, it is the complete lack of flooding that causes the
demise of its habitat.
Follow-up Activities:
1. Obtain census data for your state for the past fifty years. Plot it as a growth curve (number in
population versus time). What does it tell you about growth patterns? Comment on
implications for the future.
2. Draw a hypothetical growth curve for each of the following problems: (a) no environmental
resistance, (b) expansion of carrying capacity by technological means, (c) a population
exceeding carrying capacity, (d) introduction of a competitor.
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Cycles of Life:
EXPLORING BIOLOGY
Module 7: Ecology
Segment 2: Community Interactions
Objectives:
1. Distinguish between the terms population and community and note how they relate to each
other.
2. Identify and distinguish between different types of species interaction common in a community,
noting the direct effect of each interaction on the species involved.
3. Define and give examples of competitive exclusion, and relate this principle to the diversification
of species into different niches.
Video Synopsis:
In most parts of our country the owl is a vital predator to the larger community. Biologists Pete
Bloom and Allan Schoenherr capture and tag local owls to track their behavior and their relationships
in the environment. We learn about the nature of a symbiotic relationship, and to the associations
between predator and prey. Bloom shows us the value of competition for resources within a
community, and how three species of owl complement each other.
Questions:
1. What is a population? How does a population relate to a community?
• Population - all the organisms of one species in a given area. For example, all barn owls in
an area are one population, while all screech owls in the area are another.
• Community - all the populations in the area considered together i.e., all rodents, grasses,
ants, owls, in the area. ... all living things.
2.
What is the owl’s role in the community? Why are field studies monitoring owls important?
• Owls are predators. Their health depends on the health of their community.
• In a food chain where plants produce, then rodents eat plant parts, and owls eat rodents,
monitoring owls tells not only about owls, but also about rodents, grasses and their sources of
nutrients.
• Because owls are at the end of this chain, there are relatively few owls compared to rodents
and grasses. Small changes in numbers can have great effect.
3.
Describe the associations known as predator-prey and competition, and the role of each as
relates to the owl.
• Predator-prey - one organism eats all or part of another. Owls obtain food (a plus), rodents
are eaten (a minus). Such interactions, however, are never completely negative for the
rodent population as a whole, because they are part of the checks and balances that prevent
rodent overpopulation and help maintain better health in the survivors.
• Competition - different organisms attempting to use the same resource (food, living space,
mate, etc.) Both involved in the interaction are negatively affected. Different owl species
competing for food or even different owls of the same species would be examples.
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4. Define symbiosis and name and define three types.
• Symbiosis, living together in close association, occurs in three main types: parasitism (one
organism helped, the other harmed), mutualism (both helped), and commensalism (one
helped, the other not affected).
• Parasite-host - a special form of predation in which one organism absorbs nutrients from
the body fluids of another organism. Dodder, an orange colored growth on plants, is
considered a parasite because it taps into the sap of the host plant and takes nutrients away.
Dodder gains nutrients (a plus) while the host loses them (a minus).
• Mutualism - a close association which benefits both organisms as neither could survive well
without the other. Yucca moth requires the yucca flower to lay her eggs. Yucca flower
depends on the moth for pollination.
• Commensalism - one organism is helped while the other is not affected. If an owl moves
into an existing hole in a tree, the owl gains a home but the tree is unaffected by the presence
(or absence) of the owl.
5. Does competitive exclusion limit or expand the diversity in a given community? How?
• Competitive exclusion principle states that no two species can utilize exactly the same
resources over a period of time. One species will eventually eliminate the other (decrease
diversity) or both will specialize to reduce competition (and increase diversity in the area). ...
so both answers are possible.
• Direct competition for the same resources is harmful to both species because neither has the
resource to themselves.
• One species is always more adept than the other at utilizing the competed for resource.
• The outcompeted species must either adapt to a slightly different resource (develop a
specialized niche) or be pushed from the area.
• By specializing (having different niches), the same area can support more species ,e.g., the
oak woodland community supports three kinds of owl (horned, barn, and screech).
Follow-up Activities:
1. Describe your own unique niche in biological and physical terms. Include your interactions with
family, friends, work, and school to complete this activity. How does your niche compare with
those of animals living in the wild?
2. Assume you are attempting to introduce a new species to your community. What factors would
you consider before bringing it there? Prepare a diagram of the processes and interrelationships
you must consider and defend it to your peers.
3. Assume a new island has been built up above sea level but is 500 miles from the nearest land.
What sources are available to populate this island with both plant and animal species? What are
some of the limiting factors relating to the biodiversity on the island after many years?
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Cycles of Life:
EXPLORING BIOLOGY
Module 7: Ecology
Segment 3: Ecosystems
Objectives:
1.
2.
3.
4.
Describe an ecosystem.
Relate three important benefits of the salt marsh ecosystem.
Describe the general pattern of energy flow through an ecosystem.
Starting with producers, describe the feeding relationships and energy flow observed in
ecosystems, using concepts such as trophic levels, food chains and webs, and ecological pyramids.
Video Synopsis:
Habitats are important for migratory birds as they make their way along the Pacific pathways. The
salt marsh is especially endangered by development, and has put the Light Footed Clapper Rail under
extreme pressure for places to lay their eggs. U.S. Fish and Wildlife biologist Dick Zembal shows how
the many inhabitants of the marsh are interdependent, and we see how his activities to build nesting
areas are paying off in new Clapper Rail chicks.
Questions:
1.
What constitutes an ecosystem?
• Ecosystems include all of the living organisms, the so-called biotic components in an area,
along with all aspects of the physical environment such as light, soil, and moisture.
• The physical components of an ecosystem are called abiotic factors.
2.
How does the salt marsh ecosystem benefit various organisms?
• The marsh provides a nursery for ocean fish. It is free from the large marine predators
encountered in the ocean and has ample food.
• The marsh provides a stopover for migratory birds. It serves as a buffer against the flooding
of neighboring ecosystems.
3.
How does energy enter and pass through the ecosystem?
• Solar energy enters the ecosystem through the process of photosynthesis where it is stored in
the bonds of organic molecules.
• Some of this energy continues through the ecosystem when the producing plants are
consumed by herbivores, or primary consumers.
• In turn, dwindling amounts of energy are made available to various carnivores when they
ingest the organic materials of their prey.
• Finally, as they recycle matter, decomposers convert the remaining amount of useful energy
into heat which leaves the ecosystem.
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4. What are the differences between a food web and a food chain?
• A food chain depicts the straight-line sequence of a selected producer followed by a specific
series of consumers, one from each trophic level.
• A web, on the other hand, is a network of interlinked food chains. The food web is desirable
because, when one link is broken, there are other alternatives for consumers to continue to
feed on.
5.
Why does the available energy decrease markedly from one trophic level to another moving up
an ecological pyramid?
• Much of the energy available at one trophic level is used by the organisms of that level to
carry out all of their necessary activities via cellular respiration.
• Also, all available nutrients from one trophic level are often not consumed by members of
the next level. Grazing animals, for example, don’t consume much of the grasses’ biomass
which exists below ground as roots.
• Finally, all of the material consumed is often not assimilated by organisms, being eliminated
as solid waste instead.
Follow-up Activities:
1. Choose some natural area near your home and try to construct a possible food web for the area.
First, identify the plants that are present as producers. Next, identify as many consumers as
you can find, and assign them to their appropriate trophic levels. Finally, try to locate any
decomposers active in your study area.
2. In terms of energy flow, describe an efficient human diet that would also conserve as many
resources as possible in order to feed a hungry world.
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Cycles of Life:
EXPLORING BIOLOGY
Module 7: Ecology
Segment 4: Biomes
Objectives:
1. Distinguish between weather and climate.
2. Recognize the shape and tilt of the earth as physical characteristics which help generate weather
and climate.
3. Define biome.
4. Explain how climate contributes to the world-wide distribution of biomes.
Video Synopsis:
Weather patterns, such as “El Nino,” are very important for the continuation of living habitats. In
this segment, we learn about how the long term effects of weather patterns help define the biomes of
the earth. Dr. Warren Blier shows how regional weather patterns can change the ecosystems and
eventually, an entire biome. Mark Poth of the U.S. Forest Service, defines the major biomes, and
shows us that biological organisms are sometimes the smaller players in the larger drama between land
masses and the patterns of weather that develop in each biome.
Questions:
1
Are weather and climate interchangeable terms?
• Weather is the expression of such abiotic factors as moisture, humidity, temperature, and
wind in an ecosystem at a particular time.
• Climate, on the other hand, is the prevailing weather pattern at a particular location. It is
basically an average of the weather patterns experienced by that ecosystem over many years.
2.
How do the shape of the earth and its tilt affect the distribution of solar energy across the earth’s
surface?
• As they reach the earth’s surface, the sun’s rays all contain equivalent amounts of energy.
• Because of the curvature of the earth, however, the rays cover a smaller area near the equator
than they do at the poles. The result is that there is much more solar heating at the equator
than at the poles.
• Because of the earth’s tilt, the sun’s rays are more direct in the northern hemisphere in the
summer than in the winter, and this accounts for the seasons.
3. What is a consequence of the equator being warmer than the poles?
• Warm, moist air from the equator, rises and moves toward the poles. As it moves poleward,
this air cools, releasing much of its moisture in the tropics.
• As it continues away from the equator, this now dry air eventually descends again at a latitude
which is occupied by deserts.
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4. What are biomes, and what key factor is largely responsible for their locations?
• Biomes are major geographical areas characterized by certain plant-animal associations.
• Climate, the prevailing weather patterns in an area, determines the kind of vegetation which
can thrive in an area. The vegetation, in turn, dictates which kinds of animal will thrive.
5. How does the climate of an area determine the type of biome that will occupy it?
• Different kinds of plants are adapted to different sets of climatic conditions, and a given
plant will thrive only in a climate to which it is adapted.
• Grasses, for example, have their growing points at or just below the surface of the soil. This
adaptation prevents the grasses from destruction by grazing, drought, wind or fire.
Follow-up Activities:
1. Choose one kind of biome and determine its climatic characteristics. Next, determine its
dominant vegetation and identify some of the special adaptations possessed by these vegetation
types. Finally, do the same for the major animals of this association.
2. At first glance, the cold arctic tundra and hot desert would seem to be two biomes diametrically
opposed to one another; but, on the contrary, they actually share some common characteristics.
Research these biomes to determine their similarities, and try to decide why these are the two
most fragile biomes when it comes to recovering from the damages wrought by humans.
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Cycles of Life:
EXPLORING BIOLOGY
Module 7: Ecology
Segment 5: Global Warming
Objectives:
1. Discuss ways humans are and are not unique among organisms in their relationship to the
environment, and generally discuss the impact of humans on the ability of ecosystems to be selfsustaining.
2. Identify the major classes of air pollutants and their sources, and discuss the effect of these
pollutants on the earth’s biosphere.
3. Use the human growth curve and the need for increased productivity to show the
interrelationship of atmospheric changes and energy consumption.
Video Synopsis:
Since the dawn of the Industrial Age, man has been increasing the level of carbon dioxide in the
atmosphere at an unprecedented rate. Whether from mechanical sources or the burning off of
forests, this rising level of CO2 is of great concern to Dr. Walter Oeschel. In an attempt to
determine the effect of this and other gasses on vegetation, Dr. Oeschel has built a number of minigreenhouses where the CO2 concentrations can be closely monitored. It is with this experiment in
the background that we learn of the concern about rising CO2 levels and the possibility of massive
global warming as a result.
Questions:
1 Describe how humans have affected the biosphere in both positive and negative ways.
• With control over agriculture and fire, humans began to push previous limits on population
size, which other organisms have not been able to do.
• Growing population size increased resource use and increased the impact in populated areas.
• Industrial Revolution markedly increased pollutants and resource consumption and made the
impact global.
• Yet this same ability to manipulate and understand our environment and consciously control
our behaviors may hold hope for the future. We can avoid behaviors that damage, and
instead act to preserve the biosphere.
2. What are some common air pollutants and their sources? How can humans deal with them?
• Particulate matter (dust, asbestos, lead), hydrocarbons, oxides (nitrous oxide, sulfur dioxide,
etc.) All these pollutants come from combustion from cars, factories, and power plants.
Most can be reduced by tighter emission controls and cleaner burning practices. They will
not be eliminated until burning ceases.
• Chlorofluorocarbons (CFC’s) come from refrigerators or cans with propellants. By
international agreement (1992 Montreal Protocol and others) due to be phased out by 2010
(however, effects of current ozone damage will last 200 years or more).
• Carbon dioxide and carbon monoxide. Also from combustion (cars, factories, power plants) Not as readily cleaned from exhaust by current techniques. Will continue to be problematic
until combustion is reduced.
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3.
What is the “greenhouse” effect? Why is it more difficult to solve than other air pollution
problems?
• When gases such as carbon dioxide and water vapor collect in the atmosphere, they allow
light rays in, but trap heat energy, not letting it exit. The result is a warming of the globe.
• Effect caused by anything that increases greenhouse gases including all forms of combustion
(especially of fossil fuels) and all forms of respiration.
• It is very difficult to control; first, because carbon combustion is so common world-wide with
no readily available alternatives for energy production; and second, because the
interrelationships of carbon dioxide and organisms is very complex and not well understood.
Often factors causing the warming effect may be thousands of miles away so cause and effect
are difficult to correlate.
• Some questions remaining: What is the effect of changing carbon dioxide levels on
photosynthesis (which removes carbon dioxide)? Will changes be long-term or short-term?
Will other natural system be affected (example: warming melts polar ice which increases
decomposition which further increases carbon dioxide production-- will this become a
positive feedback loop?)
• Some other problems are easier to resolve because they are not as complex (CFC’s come
from few things and substitutes are available... so stop using them) or are more localized
(control particulate emisions in areas where such pollutants are concentrated).
4. What is being studied in the greenhouses, and how will the results be used?
• Oeschel is carefully regulating CO2 levels while controlling other variables and measuring
effects on plants over a long period of time.
• He can regulate CO2 from preindustrial levels up to two times current levels.
• Some plant measurements he is taking: overall rate of photosynthesis, carbon uptake, carbon
flux rates, metabolic rate of plants, stem growth.
• He will use the information obtained to better understand complex interrelationships
involving carbon dioxide. Each relationship will be programmed into computer-based “global
warming” models to improve their accuracy.
5. Could global warming simply be a part of the long-term climatic cycles which include periodic ice
ages as well? Explain.
• Certainly the planet has gone through cyclic changes in temperature and even carbon dioxide
levels (which correlate well). There have also been periods of mass extinctions and other
changes in biota related to such changes.
• The rate of change, however, is unprecedented. CO2 is 30% higher than it was 100 years ago,
a very short period of time in evolutionary terms.
• An undeniable mass of evidence points to a direct correlation between human activities
(combustion, deforestation) and the CO2/temperature rise.
• The question is not whether earth will survive such a rapid temperature shift, but will we and
the other organisms which share the planet with us.
Follow-up Activities:
1. Take a closer look at your home, garage, workplace or school environment. Make a list of all
the airborne contaminants to which you are exposed. Make a plan to reduce or eliminate your
exposure, that complies with environmental and safety laws.
2. Use current resources in the library to review the problem of ozone and what has been done to
help reverse the trend. Be sure to include the Montreal Protocol of 1992. Is the problem
completely gone?
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Cycles of Life:
EXPLORING BIOLOGY
Module 7: Ecology
Segment 6: Bioremediation
Objectives:
1. Identify the major sources of water pollution, describe their general effects on living organisms,
and discuss the challenges of maintaining water quality in the modern world.
2. Define bioremediation and discuss its potential for the future.
3. Use the human growth curve and the need for increased agricultural productivity to show the
interrelationship of changes in water use, land usability, and ecosystem diversity.
Video Synopsis:
Not all pollutants are man made. At Kesterson Reservoir, the runoff from irrigation of the farmers’
fields caused a leaching of the element selenium, which resulted in great harm to the migratory birds
using the area. In a radical approach, Dr. William Frankenberger opposed the permanent closing of
the reservoir, instead coming up with a mix of selenium-eating fungi and bacteria that have since
cleaned up the area and made it habitable for wildlife. In this segment, we hear how this new form of
biological cleanup, known as bioremediation, holds promise for many of the most polluted areas of
our world.
Questions:
1. What are major sources of water pollution in the modern world?
• Agricultural runoff (sediments, pesticides, metals and salts, organics)
• Wastes from factories and powerplants (chemicals and heat)
• Sewage (organic waste and potentially harmful organisms)
2. What is bioremediation and why is it attractive as a waste management process?
• Use of micro-organisms, chiefly bacteria and fungi, to break down toxins to harmless
byproducts.
• Attractive for several reasons: easy to maintain, inexpensive, can treat large areas, destroys
the toxin does not simply bury it.
3.
Why can’t microbes that naturally clean up the environment continue to do so as in the past?
• The microbes continue to metabolize wastes as they always have.
• They are being presented with mammoth quantities, however, thanks to the growth curve
(too many humans) and the agricultural and industrial revolutions that support us.
4. What was Frankenberger’s basic research and how did he apply it to the selenium problem at
Kesterson?
• At a basic research level, Frankenberger was studying the metabolism of bacteria and fungi.
He was investigating environmental factors that might increase and decrease their metabolic
rate.
• He found that items like manure or orange peel in soil would increase the metabolism of
selenium.
• By testing larger areas, he found that massive infusion of orange peel or manure would cause
the fungi to rapidly add a methyl group to selenium and convert it to a gas which would
completely remove it from the area.
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5.
With what other wastes might bioremediation work? What other techniques might be practical
for implementation?
• Pesticides, fossil fuel spills, military bases, toxic land fills.
• Potentially consider using techniques on waste streams, before build-up becomes a problem.
Follow-up Activities:
1. Describe your local recycling program. What additional materials would you like to see recycled?
Do you think bioremediation might help?
2.
Collect environmentally related articles from your local newspaper and bring them to class for
discussion.
3. Obtain a copy of the water quality report from your local water supplier. This is a public record
and is sent to each customer annually. Note the number and types of compounds listed and
compare these compounds with a current list of known or suspected carcinogens. Although the
levels are below toxic levels, discuss potential implications of long term consumption of this
water.
4. Obtain a copy of an environmental impact report from your city planner. Using similar criteria
and your knowledge from your biology course, outline a report on a parcel that is zoned for
industrial use.
5. Prepare a speech for an audience of your peers for Earth Day. What would be your main theme
and how would you inspire the students to action?
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