Download CHAPTER 6 POPULATION BIOLOGY

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CHAPTER 6 POPULATION BIOLOGY
Chapter Objectives
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Describe the dynamics of population growth.
Summarize the BIDE factors that increase or decrease populations.
Compare and contrast the factors that regulate population growth.
Identify some applications of population dynamics in conservation biology.
Key Terms
Boom and bust life cycle
Density-dependent
Density-independent
Doubling time
Influx
Oscillation
Proportion
Rule of 70
Survivorship curves
Viable
Concept Review
6.1
Dynamics of Population Growth
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All the members of a species living in an area at the same time form a
population.
Unrestricted increase in population size is exponential growth.
A graph of exponential population growth appears as a J curve.
Biotic potential refers to population growth if there are no interfering
factors.
The Rule of 70 is used to determine the approximate doubling time of
a population.
Carrying capacity is the maximum number of individuals an ecosystem
can support.
Populations may experience oscillating cycles of population growth
and decline.
Some species regulate population growth according to the supply of
resources.
A logistic growth curve, which appears as an S, or sigmoid, illustrates
population size limited by resource availability.
Organisms with a high rate of reproduction followed by a high mortality
rate are described as r-adapted species.
Organisms with exponential growth patterns are generalists,
depending upon quantity of numbers to ensure survival of some.
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6.2
Complicating the Story: r = BIDE
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6.3
Mortality is the death rate of a population.
Major factors in mortality include predation, disease, accidents, and
environmental influences.
Growth= B+I-D-E
Factors That Regulate Population Growth
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6.4
Organisms that reproduce more slowly as the population approaches
carrying capacity are K-adapted species.
Organisms that are K-adapted produce fewer offspring, are larger in
size, and live longer.
Abiotic factors affect population growth independent of the population’s
density.
Natural disasters, weather, and climatic change over a period of time
are density-independent factors.
Biotic factors affect population growth in a manner that is dependent
upon the density of the population.
Predator-prey relationships and territoriality are biotic factors that are
density-dependent.
Stress and crowding affect the rate of reproduction in dense
populations.
Conservation Biology
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The minimum viable population size is the number of individuals
needed for long-term survival of a population.
Islands that are closer to the mainland will have larger populations and
greater diversity than islands farther away.
If there are only a few individuals in a population, genetic diversity will
be limited—the founder effect.
As individuals from a population migrate to new areas, the genetic
makeup of the population changes—genetic drift.
Populations that are geographically isolated from each other but have
intermittent gene flow between them form metapopulations.
Class Time: The Acorn outline suggests 10 to 15 percent of the class be used
to study populations and demographic transition. Plan to spend 5–7 days on this
chapter, emphasizing data interpretation.
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Approach and Tips
Students are not allowed to use calculators on the AP exam, so make sure they
can perform all mathematical operations without this tool. Have students practice
the Rule of 70 to learn the doubling time of different populations. Students need
to remember to do the following for every problem:
Write the equation.
Write the information they are given.
Place the numbers in the equation and
perform the mathematical operations.
Write the answer, including the appropriate label for the units.
On the AP exam, points may be earned for each of these steps, even if the
calculation is incorrect.
Look for data and activities relating to predator-prey interactions. Project
Learning Tree has several lesson plans dealing with deer populations.
Table 6.1
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Discuss the reproductive strategies of r-adapted and K-adapted species.
Students should be able to provide information on at least one plant and animal
of each type.
Figure 6.8
Figure 6.8 illustrates the three basic types of survivorship curves. Discuss each
curve using the specific organism given, or have students name a different
organism that fits the pattern. Make sure students are able to give specific units
of time for humans.
Applications
1. Have the students plot exponential growth. Remember; do not let the
students use a calculator to do this. The rule in my class is that if I find a
calculator out, the student immediately loses 30 points on the activity or lab. If
students do not practice doing the math without a calculator they will forget how
to do it on the AP test where calculators are not allowed.
Activity: Suppose you have $1,000 in the bank and it grows at 10% a year. To
simplify the problem, assume that the interest is compounded only one time each
year and you can ignore the cents and round to the nearest dollar. Graph (by
hand) the growth of your account for 50 years and answer these 2 questions.
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What is the doubling time?
How much will be in your account after 50 years?
Grading:
• Use graph paper
• Axes labeled
• Scale and units indicated
• Scale is consistent
• Title the graph
2. Duckweed Lab
A population count using Duckweed is an easy lab. Duckweed (Lemna major) is
a small, plant that looks like a mini lily pad. It can be found in some local ponds
and lakes. Duckweed can be ordered from supply catalogs or I find it by calling
around to local plant nurseries that sell water garden supplies and have it taking
over their ponds. These nurseries are usually happy to give you all that you can
carry home for free. Some local fish supply stores will also get it in with their
aquatic plant shipments and will allow you to remove it from the aquariums for
them.
Take large test tubes and have each group of students (2-4 in a group) pick out
with forceps four individual duckweed. Duckweed reproduces both sexually and
asexually and will reproduce until it completely covers the container. As it
continues to reproduce, some will be forced down under the water and will die.
This lab is perfect for demonstrating exponential growth and carrying capacity.
Each day record the number of Duckweed found in the test tube. It will take
about 2 to 3 weeks for the Duckweed to grow exponentially and then reach the
carrying capacity. You can then have the students graph the data and have
them answer conclusion questions.
Date
Days Elapsed
Number of Individuals
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Conclusion:
1. Has this population reached the carrying capacity of the test tube?
2. What are the limiting factors for population growth of Duckweed?
3. What would happen in a lake or pond if Duckweed completely covered the
surface? What environmental effects might this have?
4. Can any organism exhibit exponential population growth forever? What
happens to a population that is above its carrying capacity?
5. Do you believe there will be a point when the human population, which is
growing exponentially, will reach the carrying capacity of the earth? Why or
why not?
Common Mistakes and Misconceptions
Make sure that the students can solve the Rule of 70 without a calculator. The
Rule of 70 is almost certain to be a question they will be asked on the AP exam.
Have students solve it by giving them the growth rate and have them determine
the doubling time and also by giving them doubling time and having them
determine the growth rate. The formula is:
70/growth rate = doubling time
Suggested Website
A good website for population (though it is dealing more with human population
issues which will be covered in the next chapter) is found at
http://www.populationconnection.org/. This organization used to be called Zero
Population Growth or ZPG but is now known as Population Connection. There
are activities, free posters, and workshops, as well as information and ways to
get involved. It is a good site to get facts on population and the environment,
population and global warming, and how population affects water, women’s
rights, and wildlife.
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Questions
1. A female cockroach can have 80 offspring every 6 months. Calculate the
population growth for five generations. What factors would limit the growth of
the population? Is this population a K-adapted species or an r-adapted
species? Explain why.
2. Abiotic factors tend to be density-independent. A collection of plants that is
successful when receiving 10 hours of sunlight per day is placed in a location
that receives only 6 hours of sunlight per day. Discuss what will happen to the
population over time and explain your reasoning.